Grow a Garden

Companion Planting Guide

By Education, Grow a Garden, Spring

Companion planting is the practice of growing different crops near one another to enhance crop production, repel damaging pests, improve soil health, and promote biodiversity.

Three Sisters Garden
Utilizing companion planting also helps maximize your garden space, by pairing different types of plants, like tall plants to provide shade to smaller plants, vining plants like squashes to help with weed suppression, and flowering plants to attract beneficial insects. A great example of companion plantings is ancestral The Three Sisters Garden or Milpa, which includes corn, beans and squash. The corn provides a natural support trellis and shelter for beans, peas and other climbing crops. In return, these legumes provide nitrogen to the soil for the corn and squash plants. Squash and pumpkin leaves shade the smaller bean and pea plants that need sun protection and provide weed suppression.

Here is a list of the most crops and their preferred companions:

Vegetable Plant with Do not plant with
Beans Potatoes, carrots, cucumbers, cauliflower, cabbage,

summer savory, most other vegetables and herbs

Onions, garlic,


Beans, Bush Potatoes, cucumbers, corn, celery, summer savory,

sunflowers, strawberries

Beans, Pole Corn, summer savory Onions, beets,

kohlrabi, sunflower

Beets Onions, kohlrabi Pole beans
Cabbage Family (cabbage, cauliflower, kale,

kohlrabi, broccoli)

Aromatic plants, potatoes, celery, dill, chamomile, sage, peppermint, rosemary, beets, onions, thyme, lavender Strawberries, tomatoes, pole beans
Carrots Peas, leaf lettuce, chives, onions, leek, rosemary,

sage, tomatoes

Celery Leek, tomatoes, bush beans, cucumbers, pumpkin, squash
Corn Potatoes, peas, beans, cucumbers, squash, pumpkin
Cucumbers Beans, corn, peas, radishes, sunflowers Potatoes, aromatic


Eggplant Beans
Leek Onions, celery, carrots
Lettuce Carrots and radishes (lettuce, carrots, and radishes

make strong team grown together), strawberries, cucumbers

Onion/Garlic Beets, strawberries, tomato, lettuce, summer savory,

chamomile, beans (protects against ants)

Parsley Tomatoes, asparagus
Peas Carrots, turnips, radishes, cucumbers, corn, beans,

most vegetables, herbs (adds Nitrogen to soil)

Onions, garlic,

gladiolus, potatoes

Potato Beans, corn, cabbage, horseradish (should be

planted at corners of patch), marigold, eggplant (as a lure for Colorado potato beetle)

Pumpkins, squash,

cucumber, sunflower, tomato, raspberries

Pumpkin Corn Potatoes
Radish Peas, nasturtium, lettuce, cucumbers
Soybeans Grows with anything; helps everything
Spinach Strawberries
Squash Nasturtium, corn
Sunflower Cucumbers Potatoes
Strawberry Bush Beans
Tomatoes Chives, onion, parsley, asparagus, marigold, nasturtiums, carrots, limas Kohlrabi, potatoes, fennel, cabbage
Turnip Peas

Here is a list of the most commonly planted herbs and their preferred companions

Herbs Companions and Effects
Basil Companion to tomatoes; dislikes rue intensely; improves growth and flavor;

repels mosquitoes and flies.

Beebalm Companions to tomatoes; improves growth and flavor.
Borage Companion to tomatoes, squash, and strawberries; deters tomato worm;

improves flavor and growth.

Caraway Plant here and there; loosens soil.
Catnip Plant in borders; deters flea beetles.
Chamomile Companion to cabbages and onions; improves growth and flavor.
Chervil Radishes; improves growth and flavor.
Chives Companion to carrots; improves growth and flavor; plant around base of fruit

trees to discourage insects climbing trunks.

Dill Dislikes carrots; improves growth and health of cabbage.
Fennel Plant away from the garden; most plants dislike it.
Garlic Plant near roses and raspberries; deters Japanese beetle; improves growth and

health; plant liberally throughout the garden to deter pests.

Horseradish Plant at corners of the potato patch to deter potato bugs.
Hyssop Companion to cabbage and grapes; deters cabbage moth; keep away from


Lamb’s Quarters This edible weed should be allowed to grow in moderate amounts in the garden, especially in the corn.
Lemon Balm Sprinkle throughout the garden.
Marigolds The workhorse of the past deterrents; plant throughout garden especially with

tomatoes; it discourages Mexican bean beetles, nematodes, and other insects.

Mint Companion to cabbage and tomatoes; improves health and flavor; deters white cabbage moth.
Marjoram Plant here and there in the garden; improves flavor.
Nasturtium Companion to tomatoes and cucumbers.
Petunia Protects beans; beneficial throughout the garden.
Purslane This edible weed makes good ground cover in the corn.
Pigweed One of the best weeds for pumping nutrients from the subsoil, it is especially

beneficial to potatoes, onions, and corn; keep weeds thinned.

Rosemary Companion to cabbage, bean, carrots, and sage; deters cabbage moth, bean beetles, and carrot fly.
Rue Keep it far away from sweet basil; plant near roses and raspberries; deters

Japanese beetle.

Sage Plant with rosemary, cabbage, carrots, beans, and peas; keep away from cucumbers; deters cabbage moth and carrot fly.
Summer Savory Plant with beans and onions, improves growth and flavor; deters bean beetles.
Tansy Plant under fruit trees; companion to roses and raspberries; deters flying insects,

Japanese beetles, stipend cucumber beetles, squash bugs, and ants.

Tarragon Good throughout the garden.
Thyme Plant here and there in the garden; it deters cabbage worms.
Yarrow Plant along borders, paths, near aromatic herbs; enhances essential oil


Adapted from Organic Gardening and Farming, February 1972, pp. 32-33, 54, and The Encyclopedia of Organic Gardening, Rodale Press, Inc., 1978, pp. 233-235.

Strategies to Combat Hail

By Education, Grow a Garden, Spring

To Replant or Not to Replant

Although there is no single solution to mitigate the impact of a severe hailstorm, it’s sometimes helpful to take a few minutes and remember some of the strategies we can pull out of our toolboxes to help promote healing.

  • Gardens, like their caretakers, are resilient and have an amazing capacity to  ‘come back’ in the most challenging situations. For a few days after a severe hailstorm, allow for grieving to occur but don’t concentrate on this aspect.
  • Carefully look for signs of new growth, and realize that given the crop or time in the season in which hail occurs, many plants will have time to recover.
  • After several days, spread about ½ inch of aged, landscape – based compost around all plants, and, using a hoe, hand trowel, or other type of cultivating tool, lightly dig it into the soil, taking care to not dig deeply or damage roots. Hail Storms lead to hard, crusted soil and a light cultivation not only opens air channels but also allows for the slow release of nutrients obtained from compost.
  • Tomatoes have the benefit of producing new side shoots from many of the leaf nodes so watch for this new growth before pruning them back.
  • Prune back damaged tops of eggplants and peppers to an outward facing node.
  • Remove shredded leaves that may be on the soil surface to prevent places for slugs, cutworms and other moisture – loving critters to move in.
  • Use a foliar spray (a spray bottle is fine) with one tsp. of liquid kelp per pint of water & spray all foliage with this solution.  Kelp provides many micronutrients and also compounds known as cytokines that stimulate and strengthen new plant growth.
  • Remove outer leaves of damaged lettuce and squash, to stimulate new growth.
  • Replant seeds of collards, summer squash, basil and beans. There’s plenty of time left in the season for them to flourish.
  • Plant marigolds and zinnias around the edges of beds to attract beneficial pollinators.
  • Consider erecting windbreaks of fallen branches near crops to break the force (next time, of course) of pounding rain, wind and/or hail. Branches can be erected in ‘teepee like’ structures to straddle rows of taller crops. If crops are low enough, a basic cover of several layers of garden row cover (often sold as ‘season extenders’ or frost protection) placed directly over the crops and weighted down with rocks or soil at the bottom may provide some protection.

Most of all, celebrate you! Realize that you play an essential part in the garden’s recovery. Hail is a natural part of our Colorado landscape—but so are the incredible blue skies, relatively few problems with disease-causing organisms and smiles we gain from noticing that first new shoot that seems to stand out so strongly as a survivor—a testament to the caring spirit of you—that special person working in partnership with the earth.

Guide to Container Gardening

By Education, Grow a Garden, Spring

Container gardening refers to the gardening practice of cultivating plants in pots, tubs, or other containers instead of directly in the ground or in raised beds. Container gardening allows for food, flower, and herb production in locations where traditional gardens are not possible or accessible, including patios, balconies, decks, and sites with poor soil quality. They are a great option for renters, individuals with limited mobility, gardeners seeking to extend the growing season, and beginner gardeners looking to start their gardening practice gradually.

The portability of containers allows gardeners to choose micro-climates for each plant based on their preferred temperature and level of sunlight. Please refer to the instructions on the back of your seed packets for more information about the preferred micro-climate of your plant varieties. 

Keep in mind that containers are more susceptible to high temperatures and moisture loss than traditional gardening arrangements. You can mitigate damage to your plants by watering the base of the plant only, checking water level daily, covering the soil with mulch, and, if necessary, using shade cloth to lessen the sunlight’s intensity. 

When growing plants in containers, pay special attention to the type of soil that you use. Soil from garden beds or your yard is generally too dense for container gardening. Instead try a lightweight potting mix.

Most garden centers will carry general purpose potting mixes or mixes specifically designed for container gardening. Or create your own soil substitute for container gardening by mixing 3 parts organic compost, 3 parts peat moss or coconut coir, and 1 part vermiculite.

Plants grown in containers often need additional nutrients since potting mixes don’t provide the same nutritional profile as garden soil. Use an organic based fertilizer several times during the season.

Remember to always add mulch (such as straw, not wood chips) on top of your soil in containers to reduce moisture loss from intense Colorado sunlight.

Tips for choosing containers 

  • Use containers at least 8” in depth for all plant varieties other than herbs and lettuces, and much larger containers will be required for many plant varieties. 
  • In general, the larger the container, the better. More soil and space will allow plants to thrive and generate larger harvests. 
  • Always use containers with drainage holes on the bottom or drill drainage holes into containers that do not already have them. 
  • You can increase harvest yield for some plant varieties (such as potatoes) with specialized planters adapted to the unique features of certain plants.

Tips for selecting plant varieties

  • Always select plants based on the amount of light available in your space. Refer to the back of seed packets for this information. 
  • Consider planting more than one plant variety together in a container. Companion gardening is most effective when you choose plants that have physical characteristics that aid each other’s growth. Common companion plants for container gardening include: 
    • Beans, Carrots, and Squash
    • Eggplant and Beans
    • Tomatoes, Basil, and Onions
    • Lettuce and Herbs
  • Companion plants should have a diversity of root depths to limit competition for water. 
    • Common shallow root plant varieties include: chives, lettuce, radishes, salad greens, basil, cilantro, beans, garlic, kohlrabi, onions, peas, mint, and thyme.
    • Common deep root plant varieties include carrots, chard, cucumber, eggplant, fennel, leeks, peppers, spinach, parsley, rosemary, beets, broccoli, okra, potatoes, and summer squash. 
    • Most, but not all, plant varieties are adaptable to growing in containers. Common varieties that are generally not adaptable to container gardening include deep-root plants such as corn or sprawling plants with extra large yields like pumpkins and melons. 
      • Varieties with ‘Patio’ or ‘Dwarf’ in the title are container friendly.

Container gardening can be very resource intensive. You’ll need to acquire large containers and enough soil to fill them. 

Tips for making container gardening cost effective

  • Consider recycling existing containers such as buckets or tubs into plant containers. Make sure to thoroughly clean and disinfect recycled containers using chlorine free bleach before planting.
  • Buy your soil and soil amendments in bulk rather than in bags.
  • Order a seed, seedling, and educational resource kit through DUG’s pay-what-you-can with a free option annual program called Grow a Garden
  • Get your seeds for free from DUG every spring in our office (1031 33rd St. St #100, Denver, CO 80205)!



  • CSU Extension “Colorado Gardening: Challenge to Newcomers” Guide 
  • Dustin Wright of Living Earth Designs

Effective Water Conservation Techniques

By All Seasons, Education, Grow a Garden

Gardening in Colorado mandates the conscious use of effective water conservation techniques. We believe community gardens should be models of efficient water use, especially in seasons of drought. Additionally, use of water conservation techniques has several other benefits including reduced water costs and weed proliferation.

If you apply the following techniques, plants will respond by growing quickly and producing an abundant harvest. We have also outlined a set of water restrictions required of all community gardeners in response to the on-going drought. Regardless of the duration of the drought, however, DUG advocates gardeners adopt and incorporate these techniques as a way of life.

Water Plants in the Cool of the Day, Especially During the Evening
Watering first thing in the morning or an hour or so before sunset, allows plant roots to utilize moisture more efficiently. Late-day watering allows the water to percolate into the soil for 12 hours or more before the sun and wind magnify the effects of evaporation and transpiration from soil and foliage.

Mid-day watering is a poor use of gardening time and an extremely inefficient way of watering into thirsty soils. Since plants do a significant amount growing at night, it makes sense to provide moisture prior to this critical period. 

Water the Roots and Soil, Not the Leaves
Although some plants, such as the broccoli family and lettuces, do not mind overhead watering and moist leaves, most vegetables prefer watering at soil level. Tomatoes, peas and members of the squash and melon families can suffer from disease problems that proliferate on wet foliage. 

Cultivate the Soil Before Watering
Hoe the soil around plants at least once a week. This serves a dual purpose—cutting off germinating weeds that compete for moisture and opening up our heavy clay soil so that water can more easily penetrate to deeper levels. Watering should be done after cultivation, while the soil is loose and airy.

Compost Throughout the Season
Compost should be applied at the beginning of the gardening season, digging two inches of compost into the top 4 – 6 inches of soil, as well as several other times during the summer and fall.

Spread a shovel-full of compost around vegetables, flowers and herbs, lightly cultivating the soil to incorporate the organic material. Since compost has the ability to hold up to 100% of its weight in water, this allows soils to hold and release moisture and organic nutrients slowly. Having compost-enriched soils is one of the best water conservation techniques available to gardeners.

Space Plants so that their Mature Leaves Shade the Soil Surface
Soil that is in shade, even in conditions of drought, is more capable of retaining moisture and reducing evaporation. The mini-climate that is produced by plants that are spaced so that mature leaves almost touch provides shading and cooling effects on the soil surface below. You can extend the growing season of cool season plants, such as lettuce, by growing them in the shade of taller plants such as pole beans. Their leaves provide a “living mulch” to help cool the roots of surrounding plants and to retain moisture.

Mulch Any Uncovered Soil Areas
Mulch conserves water, moderates soil temperature, helps to prevent erosion and slowly enriches the soil with humus as it decays. Pesticide-free grass clippings that have dried out for a few days, clean straw or fall leaves are all excellent sources of mulch. Exposed soil areas that are not being used for growing quickly become weedy and unsightly and are spaces where wasteful evaporation occurs. Mulch warm season crops, such as tomatoes and peppers, after the soil warms. Mulch cool season crops, such as lettuce, peas and broccoli several weeks after they have been transplanted or after they have been growing for about a month after germination.

Check the Soil for Needed Moisture
Most vegetables need about an inch of water per week for adequate growth. Poke a stick or your finger an inch to two inches below the soil surface to see if water is needed. Soils that are exposed to the sun (with no mulch), and are deficient in organic matter, will be significantly less efficient at retaining moisture and nutrient supplies than those that are shaded and compost enriched.

Wilting Leaves Do Not Always Signal a Call for Water
Plants with large leaves, such as those in the pumpkin/squash family, normally droop during the heat of the day. Plants are just minimizing the water loss (due to transpiration) and watering them at this time will increase water loss rather than lessen it. It also weakens the plants by promoting shallow rooting structure. 

Utilize Efficient Watering Tools
Using a hand-held watering wand with a shutoff nozzle allows you to water underneath leaves and close to the soil surface. This also breaks the force of the spray and lessens effects of soil compaction and erosion. Water with a low volume spray, as this lets water percolate deeply into the soil. Clay soils absorb water slowly. Watering for a short period of time, allowing the water to infiltrate the top layer and then re-moistening the area is a more efficient watering technique rather than short, intense watering. As an option to hand watering we suggest the use of black soaker hose snaked through your garden at the base of your plants.

Harvest Frequently
Harvest crops while plants are actively producing and healthy. Overgrown, insect and/or disease- laden plants should be removed and the area replanted to another type of plant or seeded with a cover crop. When the plant is taking more out of the soil than it returns, it is time to concentrate on soil improvement.

When to Harvest? Follow These Guidelines to Get the Best from your Garden

By All Seasons, Education, Grow a Garden

Part of having a garden is enjoying vegetables, fruits, and herbs at their peak. Follow these guidelines to get the best of your garden.

Asparagus: Begin harvesting when spears are 6-8 inches tall and about as thick as your small finger. Snap them off at ground level and new spears will continue to grow. Stop harvesting about 4-6 weeks after the initial harvest, to allow the plants to produce foliage and food for themselves.

Beans, Green: Pick before you can see the seeds bulging. They should snap easily into two. Check daily. It doesn’t take long for beans to go from tender to tough. 

Beets: Harvest and eat the greens that you thin out of the rows. It’s a matter of personal preference when it comes to the right size for harvesting. They are ready any time after you see the beets shoulders protruding at the soil line. 

Broccoli: We eat the unopened flower buds of broccoli, so check frequently, especially as the weather warms up, to ensure you don’t let the flower heads bloom. Don’t expect your home grown broccoli to get to the size of supermarket heads. Harvest when the buds are about the size of a match head. Use a knife to cut below the main crown to harvest. Once the central crown is harvested, smaller broccoli spears will grow as side shoots.

Brussels Sprouts: The sprouts will mature from the bottom up. You can begin harvesting once the sprouts are at least an inch in diameter. Harvest by twisting off or cutting the sprout from the stem. 

Cabbage: The cabbage head will feel solid when gently squeezed. Cabbage needs to be harvested when it reaches maturity or it will continue to grow and split open. Use a knife to cut at the base of the head. Large cabbage leaves that surround the head can also be harvested and used like cabbage. 

Carrots: Carrots can be hard to judge. The tops of the carrot will show at the soil line and you can gauge when the diameter looks right for your variety. If the diameter looks good, chances are the length is fine too. Pull one to be certain. Carrots can be left in the ground once mature. A light frost is said to improve and sweeten the carrot’s flavor. 

Cauliflower: Like broccoli, your homegrown cauliflower heads will probably not match supermarket size. Harvest when the head looks full and while the curds of the head are still smooth. Cut at the base of the crown with a knife.

Corn: About 3 weeks after silks form, they will dry and brown. Kernels should exude a milky substance when pricked. 

Cucumber: Check daily and harvest young. Timing and length will vary with variety. The fruits should be firm and smooth. Over ripe cucumbers can be very bitter or pithy, even before they start to turn yellow.

Eggplant: Slightly immature fruits taste best and should be firm and shiny. Cut the fruit from the plant. 

Garlic: Cut scapes off as soon as they mature, this encourages bulb formation. Garlic tops will fall over and begin to brown when the bulbs are ready. Dig, don’t pull, and allow to dry before storing. Brush off the dirt instead of washing.

Kale: Kale leaves can be harvested throughout the season. They should be a deep green with a firm, sturdy texture. Kale flavor is best in cooler weather. Harvest the largest outer leaves on a plant by simply grabbing a hold of the stem and pulling down. 

Kohlrabi: For the best texture, harvest once the kohlrabi bulb has reached about 2-3 inches in diameter. The bulbs become tougher as they grow and age. Pull or slice at the base. 

Leeks: Harvest leeks when they are about 1 inch in diameter. 

Lettuce, Head: Harvest once the head feels full and firm with a gentle squeeze. Hot weather will cause it to bolt or go to seed rather than filling out. Pull the entire head out. 

Lettuce, Leaf: Harvest the outer leaves once the plant has reached about 4 inches in height. Allow the younger, inner leaves to grow. Leaf lettuce can be harvested in this fashion for most of the summer.

Melons: There are many varieties of melons, but a general rule of thumb is that the color should change to beige and the fruit will slip from the vine when lifted. You should also be able to notice a sweet smell when ripe. 

Onions: Onions can be dug once the tops have ripened and fallen over. Brush the dirt off rather than rinsing and allow the onions to dry in the sun. 

Parsnips: Parsnips taste best if they are left in the ground until after a frost or two. They can be left in the ground over the winter and harvested in the spring. In cold areas, they should be mulched for the winter.

Peas: The pea pods should look and feel full. Peas are sweeter if harvested before fully plumped. Peas really need to be tasted to determine if they are sweet enough. 

Peppers: Each variety is different, but generally, peppers should be harvested when they turn the expected color. Carefully cut the pepper from the plant.

Potatoes: ‘New’ potatoes can be harvested when the tops start to flower. Carefully dig at the outer edges of the row. For full size potatoes, wait until the tops of the potato plants dry and turn brown. Start digging from the outside perimeter and move in cautiously to avoid slicing into potatoes. 

Pumpkins: Once the pumpkins have turned the expected color and the vines are starting to decline, check to make sure the skin has hardened enough that poking it with your fingernail will not crack it. Do not pick your pumpkin too soon because it will stop turning orange once it’s cut, but don’t leave them out in a hard frost either.

Radishes: Radishes mature quickly. You will see the shoulders of the bulbs popping out of the soil line. If left too long, they will become tough and eventually go to seed. 

Rutabaga: The bulbs should be about 3 inches in diameter, generally about three months after setting out. Rutabagas can be mulched, left in the ground and dug up as needed. Cold weather improves their flavor.

Swiss Chard: As with leaf lettuce, cut the large outer leaves at the base of the stem—being careful not to cut new growth—and allow the center to continue growing. 

Spinach: Spinach goes to seed quickly. Harvest by cutting at the soil line before you see a flower stalk emerging.

Squash, Summer: Pick young and check often. The skins should be tender enough to poke with your fingernail.

Squash, Winter: Color is a good indicator of winter squash maturity. When the squash turns the color it is supposed to be, cut from the vine. Do not let winter squash be exposed to frost. 

Tomatoes: Harvest when they are fully colored and slightly soft to the touch. Gently twist and pull from the vine. 

Turnips: Turnip shoulders should be about 2” in diameter at the soil line when ready. Overripe turnips are woody. 

Watermelon: The white spot on the bottom of the melon should change to a deep yellow when ripe. You may hear a change in the sound made when the melon is thumped with a finger. It should make a hollow sound when ripe.

Source: Gardening About

Tips for Successful Gardening in Colorado

By Education, Grow a Garden, Spring

Gardening in Colorado requires careful attention to seasonal variations, correct watering techniques and soil preparation. However, with 300 days of sunshine, disease problems are not as prevalent as in humid regions. Our semi-arid, mile-high altitude allows vegetables and flowers to mature quickly, with fruiting varieties, such as tomatoes, peppers and squash thriving in abundant light. For all gardeners, a little knowledge about basic gardening techniques and Colorado conditions can lead to a well managed, beautiful organic garden, with rich, productive soil and a diverse harvest.

Know When to Plant

The last spring frost is around May 15th, and the first fall frost is around October 5th.

Cool season crops, which can be planted as soon as the soil can be prepared (usually late March) include: spinach, onion seeds and sets, asparagus crowns, cilantro, parsley, potatoes, radishes, leaf lettuces, peas, green onions, collards and mustard greens. A few weeks later (mid-late April), plant carrot seeds and transplants of cabbage, broccoli and cauliflower.

Plant winter squash, pumpkins, corn, sweet basil, beans, cucumbers, and melons in the first week of May. Transplants of tomatoes are usually planted the second week in May, while heat-loving peppers and eggplants are best planted the third week in May.

Peas can be replanted at the end of July for a fall crop. Spinach, lettuce and radishes can be replanted in mid-August for a fall crop. Read individual seed packets for crop-specific information.


Prepare Soil with Adequate Organic Material 

Most Colorado soil is a heavy clay type, which needs to have at least 2 inches of compost dug into the top 3–4 inches of soil. Moisten soil a few days before digging and do not work the soil when it is wet, as it will dry like adobe brick.

Dig with a shovel or garden fork, turning over small clumps of soil at least 6 inches down, breaking up clumps with the shovel to produce fine particles. Spread compost on top of the loosened soil, again mixing it into the top several inches of clay soil (where most of the root growth occurs).

Plant Only What You Like and Can Care For

  • Plan enough space for cool, warm and hot season vegetables and herbs.
  • Utilize ‘succession planting’ for fast-maturing veggies such as spinach, lettuce and peas. To ensure a staggered harvest, plant small quantities of the above crops at 1–2 week intervals.
  • Interplant shade-loving veggies, such as lettuce, with taller peas. The peas shade the lettuce and also provide nitrogen needed by the salad green.
  • Leave enough space to replant spring crops in mid-August for a fall harvest.
  • Thin all direct-seeded crops to allow room for root development.

‘Harden Off ‘ All Greenhouse Transplants
For one week, expose all transplants to outdoor growing conditions. Take them outside in a semi-shaded area for 1 hour the first day and then bring them back inside. Each day, increase their time outside by 1–2 hours. By the end of the week transplants should be able to withstand strong winds and UV exposure.

Water Gently at Root Level
Newly planted seeds need daily watering, with uniform moisture applied slowly and evenly. Avoid overhead watering of tomatoes, cucumbers, beans, squash, pumpkins and melons, as diseases can be spread with such a technique. To find out if plants need water, insert a branch or your finger several inches into the soil, if moist soil adheres to your measuring device, plants do not need water.

Cultivate the Soil Around All Plants Once a Week
Lightly scratching the soil before watering is an excellent way to keep the weed population in check and open up air channels for deeper infiltration of water. A crumbly, loose soil also allows roots to reach down further for water. Weeds can be left directly on the soil and used as mulch. 

Mulch All Areas
Use straw or dried pesticide-free grass clippings as mulch around all crops. A light covering on all bare soil provides a cooler root-growing environment, prevents erosion and conserves water.

Harvest Frequently

Overgrown produce becomes a magnet for disease and insect infestation. Harvest when veggies are small and skins are shiny (especially noticeable in eggplants). As plants slow in production, remove the crop and plant a different variety. Early peas can be followed by squash, and spinach or lettuce can be followed by beans.

Integrated Pest Management Best Practices

By Education, Grow a Garden, Spring

Integrated pest management (IPM), encourages regular monitoring of insect populations to determine when and if treatments are necessary to minimize unacceptable levels of damage. It employs the use of physical barriers, companion planting and cultural techniques, in addition to least toxic controls to maintain a proper balance between pest and predator insect. In IPM, total eradication of pest populations is not sought, since it would upset the ecological balance. 

The individual needs to determine how much pest-related damage can be tolerated (the injury or damage level) without harming the health of plants or people is more important. Following this, the pest population must be studied to assess how rapidly it will increase to produce that level of damage. The final step involves development of a treatment strategy that will keep the pest population small enough so that it does not cause an unacceptable level of damage.

Companion Planting

As part of a well managed IPM system, strategies employing intercropping and companion planting are utilized to increase crop diversity. In this system, many different herbs, flowers and even weedy ground covers are used to deter pest insects and attract beneficial predators. Insects locate their preferred food by means of sight, smell and taste. They use sensitive receptors on their feet and mouthparts to find a certain crop from a great distance (e.g. the white cabbage butterfly can recognize the mustard oils of the broccoli family from a distance of ten miles).

Plants produce substances that either attract or repel insects. These include:

  • Attractants: Some examples include mustard oils of the brassica family that attract cabbage butterflies, apple skins attract codling moths and onions produce sulfur and attract the onion maggot.
  • Stimulants: These substances encourage feeding and/or egg laying behavior. Bitter chemicals in cucumber and melon skins stimulate feeding by the cucumber beetle.
  • Deterrents: These substances inhibit feeding or egg laying. Mustard oils sicken spider mites and Mexican bean beetles.
  • Repellants: These substances force insects to move away from a plant. Citronella and catnip sprays repel many insects.

Beneficial Insects to Attract

  • Ground beetles and lady beetles
    • Attracted by clovers, tansy and yarrow for egg-laying material; eat aphids, slugs and many soft-bodied pests.
  • Hover or syrphid flies (also known as flower flies)
    • Flat, open flowers such as marigolds or daisies provide areas for egg laying. Larvae control aphids.
  • Tachinid flies
    • White clover and members of the carrot family (e.g. carrots, parsley, lovage, queen anne’s lace and cilantro) provide sites for egg laying. Adults are parasites of Mexican bean beetles.
  • Lacewings
    • Increase in numbers when provided with nearby evergreens for shelter. Adults and larvae are fierce predators of soft-bodied pests.

Flowers and Nectar and Pollen for Adult Beneficial Insects
The compositae (daisy) family is attractive to most beneficial insects and includes daisies, goldenrods, black-eyed susans, coreopsis, asters, bachelor buttons and lettuces that have bolted (sent up a seed stalk). Other flowers and herbs that attract beneficial insects include bee balm, yarrow, the carrot family, mints, hyssop and salvia.

Legumes, such as peas or beans, are used as companions to increase nitrogen levels in the soil. White clover can be used in-between corn rows, as well as peanuts. Vetch can be used as nitrogen providing mulch around fruit trees. 

Beans: Plant rosemary, marigolds and nasturtiums to repel Mexican bean beetles.
Tomatoes: Good planted with basil (a possible fly repellant) and asparagus.
Broccoli family: Try with dill, mint, sage, onions and southernwood to repel cabbage butterflies.
Chamomile: Good hosts for hoverflies and wasps.
Cucumbers: Plant with marigolds and onions.
Peas: Plant with shade lovers such as spinach and lettuce.
Carrots: Plant with peas, leeks and onions.
Garlic sprays: Combine with hot peppers and onions (blenderized) for aphid control.
Catnip sprays: Try this for control of aphids and flea beetles.
Copper strips: To repel slugs. Also, try fermented yeast traps to attract and down them. Non-alcoholic Kingsbury Malt beverage was the brew of choice (or non-choice) that provided good slug control. Pull mulch away from transplants if the weather is rainy and slugs are congregating there. 

Specific Organic Remedies (Insects and Diseases)

Pest/Disease Crop Remedy
Aphids All crops Wash off with a strong spray of water, insecticidal soap.
Corn Earworm Corn Use a few drops of mineral oil in the tips of baby corn ears or dust with Diatomaceous earth.
Cut Worms All young transplants Protect stems with a ‘collar’ made of toilet paper cores. Utilize Diatomaceous earth on the soil around transplants.
Earwigs All crops Shallow containers of beer as traps.
Flea Beetles All young transplants Garden row-covers, such as Reemay, Safer Insecticidal Soap, Neem oil, Diatomaceous earth, beneficial nematodes (use the last product for juvenile forms of flea beetles that live in the soil), available as Scanmask from Planet Natural
Mexican Bean Beetle Beans (all types except soybeans) For adult beetles: Pyganic, an organic botanical product derived from chrysanthemums. For larvae: Neem oil. Both products are available at Arbico Organics 
White Cabbage Butterfly (Cabbage Worm) Crucifer family: Broccoli, cabbage, cauliflower, turnips, Brussels sprouts, Chinese cabbage, kale Brush off eggs that are mainly laid on the underside of leaves and also brush off the larval caterpillar form of the pest. Bacillus thuringiensis kurstaki (sold as: Thuricide or Dipel), which must be ingested by the caterpillars, so it is important to spray on the underneath leaf surfaces. Neem oil (available locally) can be used as a foliar spray. 
White Grubs All transplants and seeded crops  Eat germinating seeds and young roots. Use ‘Scanmask’ from Planet Natural.
Blights (spots, brown, yellowing leaves) Mostly tomatoes Pick off yellowing leaves, water at the roots. Use Serenade, available at Planet Natural.
Powdery Mildew Summer and winter squash, cucumbers, pumpkins and melons Water plants at the roots and discard severely infected leaves. Spray leaves with a solution of: 1 Tbsp. baking soda, 2 drops dishwashing liquid or Safer’s Insecticidal Soap, 1 Tbsp. horticultural oil such as ‘Sunspray R’, mixed in 1 gallon of water.

Sources: Carr, Anne. Rodale’s Color Handbook of Garden Insects. Rodale, 1979.
Cranshaw, Whitney. Garden Insects of North America: The Ultimate Guide to Backyard Bugs. Princeton, NJ: Princeton University Press, 2004.
Cunningham, Sally Jean. Great Garden Companions: A Companion-Planting System for a Beautiful, Chemical-Free Vegetable Garden. Rodale, 2000.
Riotte, Louise. Carrots Love Tomatoes: Secrets of Companion Planting for Successful Gardening. 2nd Ed. Storey Publishing, 1998.

Vegetable Planting Guide – A Guide to When to Plant What in Denver

By Education, Grow a Garden, Spring

For first-time gardeners or those new to Colorado, it’s helpful to understand a bit about our unique climate and growing conditions. Denver’s Climate & Elevation classifies as semi-arid high desert (Zone 5b). Although we receive 60 inches of snowfall per year in Denver, we only receive between 9-15 inches of precipitation usable for gardening.

We live at high elevation and enjoy over 300 days of sunshine with intense ultraviolet radiation annually. Gardening season in Denver runs from late March to late October. Please note, not all plants thrive in the same part of the season. Your seed packets will have specific information for each plant.

The average last frost in Denver is mid-May and the average first frost is mid-October. This determines the best times to sow seeds indoors or outdoors, depending on the crop and their preferred soil and air temperatures. It also guides us as to when to plant warm weather crops outside to avoid transplant shock and stunting due to temperature fluctuations and unexpected late-season snow. 

Knowing when to plant or transplant will help you and your plants prepare for a successful growing season.

Here is a list of the most commonly planted crops and their best time to start them indoors or outdoors

warm weather
cold weather
sow indoors
sow outdoors
Start Seeds* Transplant * *Weeks before or after last frost date Fall Planting*
Bush Beans  •  •  3-4 before  1-2 after  12 before
Pole Beans  •  •  3-4 before  1-2 after  12 before
Beets  •  •  2-4 before  8-10 before
Broccoli  •  •  5-8 before  5-8 before  14-17 before
Brussel Sprouts  •  •  5-8 before  4-6 before  17 before
Cabbage  •  •  4-6 before  5 before  13-14 before
Carrots  •  •  •  2-4 before  13 before
Cauliflower  •  •  5-8 before  1-2 before  14 before
Celery  •  •  8-10 before  2-3 before  19 before
Chard  •  •  •  2-4 before  6 before
Corn  •  •  3-4 before  1-2 after  6 before
Cucumber  •  •  2-3 before  1-2 after  11 ½ before
Eggplant  •  •  6-8 before  2-3 after  14 before
Garlic  •  •  6 before  Sept. w/mulch
Kale  •  •  5 before, 2 after  6-8 before
Kohlrabi  •  •  5 before, 2 after  10 before
Leeks  •  •  8-10 before  5 before
Lettuce  •  •  •  2-4 before, 2 after  6-8 before
Onion  •  •  3 before, 2 after  8 after spring
Parsley  •  •  •  •  4-6 before  1-2 after
Peas  •  •  4-6 before, 2-3 after  12 before
Peppers  •  •  1-3 after
Potatoes  •  •  4-6 before
Pumpkin  •  •  After frost
Radish  •  •  •  4-6 before  7 before
Spinach  •  •  •  3-6 before  6-8 before
Squash, Summer  •  •  1-4 after  10 before
Squash, Winter  •  •  2 after  13 before
Tomatoes  •  •  2-4 after

Different plants have specific needs, here are some great tips:

Bush Beans: Sensitive to transplanting, pinch extra plants. Don’t pull them. Pick every 3-7 days.

Pole Beans: Sensitive to transplanting; pinch extra plants, don’t pull them. Pick  every 3-7 days.  

Beets: Thin when young and cook the tops as you’d other greens.  

Broccoli: Keep cool to get stocky plants, but don’t go below 40° F. Transplant into  beds up to first true leaves. Harvest the main head when buds begin to loosen.  Side heads will form after the first head is cut.  

Brussel Sprouts: Keep cool to get stocky plants, but don’t go below 40° F.  Harvest sprouts when they are 1 ½”  wide. Pick lower ones first. 

Cabbage: Harvest when head is formed. Keep cool to get stocky but don’t go below 40° F.  

Carrots: Thin early; harvest any size. 

Cauliflower: Tie outer leaves around head to protect from sun. Likes weather between 57°- 68° F.

Celery: Must go below 60° F at night for seeds to germinate. Requires a lot of nutrients and water.  

Chard: Cut leaves close to ground when 8-10” high. Harvest outer leaves.  

Corn: Sensitive to transplanting, pinch extra plants. Plant in blocks, harvest when kernels are milky.  

Cucumber: Somewhat sensitive to transplanting; pinch extra plants. Mound soil into hills; plant 3 seeds per hill.  

Eggplant: Grows well in hot weather. 

Garlic: Harvest when tops start to die.  

Kale: Keep cool to get stocky plants, but not below 40° F. Cut outer leaves closer to the stem when 10” or longer.  

Kohlrabi: Keep cool to get stocky plants,  but not below 40° F. Harvest when the bulb is 3” in diameter.  

Leeks: Keep cool to get stocky plants, but not below 40° F. Plant out when 4” high. 

Lettuce: Keep cool to get stocky plants,  but not below 40° F. Hard lettuce likes  repotting. Plant successively every two weeks. Will go to seed in high temperatures. Harvest outer leaves of leaf lettuce vs. head. 

Onion: Harvest when tips start to die  back.  

Parsley: Soak seeds overnight to speed germination. Cut outer leaves near the stem.  

Peas: Sensitive to transplanting, pinch extra plants, don’t pull them. Harvest frequently.  

Peppers: Sensitive to cold, harden off gradually. Green peppers turn red when ripe. 

Potatoes: Very tender; cannot tolerate frost. Dig up with a digging fork after the tops have flowered.  

Pumpkin: Sensitive to transplanting; pinch, don’t pull plants. Plant in hills, 3-4 plants per hill, 6-8 ft. apart.  

Radish: Plant every 10 days. Will get woody when over mature. 

Spinach: Keep cool for stocky plants.  Plant every 2 weeks. Will go to seed in hot weather.  

Squash, Summer: Sensitive to transplanting; pinch extra plants, don’t pull them. Harvest frequently.  

Squash, Winter: Sensitive to transplanting; pinch extra plants, don’t pull. Can store through the winter.  

Tomatoes: Prefers warm days and cool nights.

Adapted from Organic Gardening and Farming, February 1972, pp. 32-33, 54, and The  Encyclopedia of Organic Gardening, Rodale Press, Inc., 1978, pp. 233-235.