One of the most important principles of healthy soil is keeping it covered and keeping living roots growing for as much of the year as possible. Cover crops help accomplish both, protecting the soil while feeding the underground community of fungi, bacteria, earthworms, and other organisms that support healthy, productive gardens.
Cover crops are plants grown primarily to improve the soil rather than for harvest. They are often planted after summer vegetables are removed to protect and enrich the garden over fall, winter, or early spring. When cut down and incorporated into the soil or left on the surface as mulch, they become a natural source of organic matter and nutrients, also referred to as green manures
Benefits of Cover Crops
Prevent Soil Erosion: Cover crops act like a blanket, protecting soil from wind and water loss during Denver’s dry, variable winters.
Improve Soil Structure: Roots create natural channels for air and water infiltration. As cover crops decompose, microorganisms thrive, producing sticky substances that bind soil particles together, improving soil aggregation and increasing water-holding capacity.
Weed Suppression: Cover crops shade the soil and compete with weeds for light, water, and nutrients. Some, like Winter Rye, even have allelopathic properties that temporarily prevent weed seed germination.
Nitrogen Fixation: Legumes like Winter Pea, Red Clover, and Hairy Vetch partner with soil bacteria to form root nodules that store atmospheric nitrogen, releasing it into the soil when the plant breaks down. (Pro Tip: For maximum benefit, inoculate legume seeds with the appropriate Rhizobium bacteria before planting to enhance nitrogen fixation.)
Support Beneficial Insects: Flowering cover crops attract pollinators and provide shelter and food for predatory insects that reduce pest populations naturally.
Care and Management
- Planting Timing: For Denver (Zone 6a), plant cover crops mid-August through mid-September, after summer crops are harvested.
- Seedbed Preparation: Dig soil thoroughly, mix in 1 inch of decomposed compost into the top 4–6 inches, and break up large clumps.
- Sowing Seeds: Lightly rake seeds into the top ¼–½ inch of soil and press gently. Cover with a light layer of straw or chopped leaves.
- Watering: Keep soil evenly moist until seedlings establish. Once established, most cover crops are low-maintenance.
- Spring Management:
- Cut cover crops before they reach knee-high.
- Till or dig them into the soil, leaving residues on top as mulch.
- Leave some residue on top as loose mulch to protect soil from drying out.
- Wait ~2 weeks for decomposition before planting spring crops.
Recommended Fall/Winter Cover Crops for Denver
| Cover Crop | Type | Key Benefits | Planting Time | Winter Behavior & Early Spring Management |
| Winter Wheat | Cereal Grain | Protects soil from erosion, adds organic matter, keeps soil active | Mid-Aug–Mid Sept | Very hardy; till into soil in spring to enrich soil |
| Winter Pea / Austrian Winter Pea | Legume | Fixes nitrogen, improves soil structure | Mid-Aug– Early Sept |
Moderately hardy; top growth may winterkill, roots enrich soil; till before flowering |
| Red Clover | Legume | Fixes nitrogen, loosens soil, supports beneficial insects | Mid-Aug–Mid Sept | Hardy perennial; roots survive winter; mow or till before flowering |
| Hairy Vetch | Legume | Excellent nitrogen fixer, improves soil structure, supports beneficial insects | Mid-Aug– Early Sept |
Moderately hardy; may winterkill in extreme cold; till before flowering |
| Winter Rye | Cereal Grain | Very hardy; protects soil, prevents erosion, suppresses weeds, adds organic matter | Mid-Aug–Mid Sept | Very hardy; roots and biomass survive winter; till in spring |
| Daikon Radish | Brassica Root | Breaks up compacted soils, increases water infiltration, adds organic matter as roots decompose | Early-Mid Aug | Not hardy; intentionally winterkills; decomposing roots leave natural channels; rake or mulch remaining tops in spring |
Why Plant a Mix of Cover Crops?
Cover crop mixes outperform single-species plantings because each plant contributes something different.
- Grasses (oats, cereal grains) build organic matter and protect soil.
- Legumes (peas, clovers) add nitrogen.
- Brassicas (radish) break up compacted soil with deep taproots.
- Broadleaf plants (buckwheat) quickly shade the soil, suppress weeds, and support pollinators.
Together, these species create healthier soil than any one crop can provide alone.
Recommended Cover Crop Mixes for Denver
| Mix | Best Time | Benefits | Spring Management |
| Oats & Austrian Winter Peas Mix | Mid-Aug–Mid Sept | Excellent beginner mix. Oats provide quick soil cover and organic matter while peas fix nitrogen. Oats usually winterkill, leaving an easy-to-manage mulch while pea roots continue enriching the soil. | Rake or lightly incorporate residue before planting. |
| Peas, Grains & Radish Mix | Mid-Aug–Mid Sept | Multi-purpose mix combining nitrogen fixation, erosion control, organic matter production, and deep soil loosening. Radishes help relieve compaction while grasses protect the soil throughout winter. | Radishes winterkill; terminate remaining growth before planting spring crops. |
| Oats, Buckwheat & Red Clover Spring Mix* | Early Spring | Ideal for beds that won’t be planted immediately. Oats provide quick biomass, buckwheat suppresses weeds and attracts pollinators, and red clover builds long-term soil fertility through nitrogen fixation. | Cut before buckwheat sets seed and before clover flowers. Incorporate or leave as mulch before planting. |
* Unlike the other mixes listed here, this Spring Mix is intended for spring planting, not Fall. It is included as a good option for improving soil for those who won’t be able to cover crop before winter but would still like to reap the soil benefits before summer crops are planted.
Quick Tips For Success:
- Plant early enough (mid-Aug through mid-Sept) for roots to establish before frost.
- Lightly press seeds into soil; cover with a thin layer of straw or chopped leaves.
- Water thoroughly after planting; once established, most cover crops are drought-tolerant.
- In spring, cut and till before flowering for maximum soil benefit. Leave residue on top after cutting in spring to conserve moisture.
By planting cover crops, you’re feeding the soil, improving its structure, and setting the stage for a thriving, biologically alive garden next season. Small efforts now create resilient, moisture-retentive, fertile soil for years to come.
Bonus Tip: Try Undercropping
If you’re still harvesting warm-season crops into the fall, you don’t have to wait until your beds are empty to start building healthy soil.
Undercropping (also called intercropping) is the practice of sowing a cover crop 3–4 weeks before your final harvest so it can become established beneath your vegetables. This extends the time that living roots are in the soil, helping protect it from erosion, suppress weeds, and feed beneficial soil microbes.
Undercropping works best beneath upright crops that allow sunlight to reach the soil, such as:
- Tomatoes
- Peppers
- Sweet corn
It is generally not recommended beneath sprawling or dense crops like winter squash, pumpkins, or sweet potatoes, where heavy foliage blocks the light needed for cover crop seeds to germinate.
For success:
- Seed 3–4 weeks before your expected final harvest.
- Make sure the soil is moist when planting.
- Ensure enough sunlight reaches the soil surface for seeds to germinate.
- Continue watering as needed until the cover crop is established.
In conclusion, by planting cover crops, you’re feeding the soil, improving its structure, and setting the stage for a thriving, biologically alive garden next season. Small efforts now create resilient, moisture-retentive, fertile soil for years to come
