Want healthier soil this summer? Green manures are your answer. These are crops grown specifically to improve soil quality, boost nutrients, and control weeds. Here’s a quick breakdown of the best summer options:
- Sorghum-Sudangrass: Adds tons of organic matter, breaks up compacted soil, and suppresses weeds.
- Buckwheat: Grows fast, improves phosphorus availability, and attracts pollinators.
- Cowpeas: Fixes nitrogen, thrives in hot climates, and prevents erosion.
- Japanese Millet: Controls weeds, prevents erosion, and releases key nutrients.
- Sunn Hemp: Fixes nitrogen, suppresses weeds, and handles tough conditions.
Quick Comparison
| Green Manure | Key Benefits | Best For |
|---|---|---|
| Sorghum-Sudangrass | Organic matter, soil structure | Compacted, poor soil |
| Buckwheat | Quick growth, phosphorus availability | Short growing seasons |
| Cowpeas | Nitrogen fixation, erosion control | Hot, dry climates |
| Japanese Millet | Weed suppression, nutrient release | Wet or drought-prone soil |
| Sunn Hemp | Nitrogen fixation, biomass production | Challenging conditions |
These crops improve soil structure, fertility, and weed control. Choose the best one for your garden’s needs, plant at the right time, and enjoy better soil health this summer.
Homemade Green Manure For Summer
1. Sorghum-Sudangrass
Sorghum-sudangrass is a summer crop often used as green manure to improve soil health. This hybrid of forage sorghum and sudangrass is known for contributing large amounts of organic matter to the soil.
How It Improves Soil
Under the right conditions, sorghum-sudangrass can produce 4,000–5,000 lbs of dry matter per acre, with potential yields reaching up to 18,000 lbs . Its deep, spreading roots are key to improving soil structure.
"Sorghum-sudangrass hybrids are unrivaled for adding organic matter to worn-out soils." – SARE
The plant's roots break through compacted soil layers, promoting better water infiltration and aeration. Mowing at the right time can increase root mass by up to eight times, with roots reaching depths of 10–16 inches . Effective management enhances these soil benefits, as shown in the growing tips below.
Growing Tips
Timing and proper care are essential for success:
| Growth Stage | What to Do | Why It Matters |
|---|---|---|
| Planting | Sow seeds 2 weeks after corn planting | Ensures soil is warm enough |
| Early Growth | Plant seeds 1/2 to 2 inches deep | Helps access moisture |
| Mid-Growth | Mow when plants are 3–4 feet tall | Boosts root growth |
| Late Season | Disk plants while still vegetative | Speeds up breakdown in soil |
For standard biomass production, apply 75–100 pounds of nitrogen per acre . Use a seeding rate of 20–30 pounds per acre for drilled planting or 30–40 pounds per acre for broadcast planting .
Weather Requirements
This crop thrives in soil temperatures above 65°F, requires 60–90 frost-free days, and can tolerate a pH range of 5.0–9.0 .
Additional Benefits
Sorghum-sudangrass offers more than just soil improvement. It naturally suppresses weeds through allelopathic compounds and can disrupt pest cycles . Thanks to its waxy leaves and strong secondary roots, it’s also more drought-resistant than corn . When used in crop rotations, it can help rejuvenate overworked soils, bringing them closer to their original condition .
2. Buckwheat
Buckwheat is a quick-growing summer cover crop that improves soil health in just 40 days . It's an ideal choice for warm, short-season summer planting.
How It Improves Soil
Buckwheat works wonders for soil through several processes. Its thick, fibrous roots help prevent erosion and release mild acids that convert phosphorus into a form plants can absorb . These roots also enhance the effectiveness of organic fertilizers, making nutrients more accessible .
| Soil Benefit | How It Works |
|---|---|
| Nutrient Capture | Pulls phosphorus and calcium from the soil, minimizing nutrient loss |
| Soil Structure | Improves soil texture, creating loose, workable soil through root activity |
| Erosion Control | Dense root systems reduce water runoff, protecting soil from erosion |
| Organic Matter | Rapid growth generates a large amount of biomass that enriches the soil |
Timing is key to getting the most out of buckwheat's soil-improving properties.
Growing Tips
Plant buckwheat after the last frost in spring and up to 60 days before the first frost . Spread 2–3 pounds of seed per 1,000 square feet and lightly rake it into the soil .
For best results, cut or till buckwheat within 10 days of the start of flowering . After incorporating the plant material, wait about a month before planting small-seeded crops like carrots or parsnips to avoid any potential allelopathic effects .
Weather Requirements
Buckwheat grows well in cool, moist conditions but cannot handle frost. It prefers soils with a pH of 6.0–6.5 but can also grow in slightly more acidic soils (pH 5.4–6.0) if phosphorus levels are sufficient. The plant thrives in light to medium, well-drained soils such as sandy loams, loams, and silt loams .
Other Garden Benefits
Beyond improving soil, buckwheat suppresses weeds, attracts pollinators, and supports helpful insects. Its dense canopy shades out mid-summer weeds , and its flowers draw pollinators and beneficial insects. In fact, one acre of buckwheat flowers can yield about 100 to 150 pounds of honey . For tailored advice, experts at Thrive Lot (https://thrivelot.com) can help design outdoor spaces that incorporate cover crops like buckwheat.
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3. Cowpeas
Cowpeas, also called southern peas or blackeye peas, are a solid choice for summer soil improvement. They thrive in hot, dry conditions and work well as green manure during the summer months .
How Cowpeas Improve Soil
Cowpeas can produce 100–150 lb of nitrogen per acre under standard conditions and over 300 lb per acre with proper inoculation . Their deep taproots, which can reach up to 8 feet in just eight weeks, help break up compacted soil and improve its structure .
| Soil Benefit | Impact |
|---|---|
| Nitrogen Fixation | 100–150 lb/acre (up to 300 lb in some soils) |
| Biomass Production | 3,000–4,000 lb/acre |
| Root Depth | Up to 8 feet in 8 weeks |
| Erosion Control | Dense canopy and deep roots prevent soil loss |
To maximize these benefits, proper planting techniques are key.
Growing Tips
Cowpeas should be planted when soil temperatures are consistently between 65°F and 70°F. Place one or two seeds per hole, about 1 inch deep and 6 inches apart . For better nitrogen fixation, use a cowpea-specific inoculant before planting .
"With cowpeas, I get wind erosion control, add organic matter to improve soil tilth, save on fertilizer and suppress weeds for the wheat crop."
– Jim French, Farmer
For garden setups, plant double rows spaced 6 inches apart, leaving 3–4 feet between sets . Incorporate the plants into the soil while they are still green to quickly release nutrients .
Weather Requirements
Cowpeas grow best in full sun with temperatures between 70°F and 95°F. They need at least 1 inch of water per week and well-drained soil to avoid bacterial problems. Soil temperatures should be between 65°F and 85°F for successful germination .
Additional Benefits
Cowpeas do more than just enrich the soil. Their dense canopy helps suppress summer weeds, while their biomass production contributes to overall soil health . They also attract beneficial insects, aiding in natural pest control and promoting a balanced garden ecosystem .
4. Japanese Millet
Japanese millet, also known as barnyard millet, is a fast-growing summer annual that plays a key role in improving soil conditions and managing common agricultural challenges .
Benefits for Soil
With its deep root system, Japanese millet helps prevent erosion and contributes between 1,500–3,500 pounds of dry matter per acre . It also releases phosphorus and potassium into the soil, benefiting subsequent crops . Its thick canopy and natural weed-inhibiting properties make it effective at keeping unwanted plants at bay .
| Soil Benefit | Effectiveness |
|---|---|
| Releases phosphorus (P) and potassium (K) | Good |
| Controls nematodes | Good |
| Suppresses diseases | Very Good |
| Produces weed-inhibiting compounds | Very Good |
| Smothers weeds | Excellent |
This crop stands out among summer cover crops for its ability to quickly generate biomass while effectively suppressing weeds, making it a strong choice for revitalizing soil.
Planting Guidelines
Sow Japanese millet seeds between May 20 and September 6, planting them 0.5 to 1 inch deep in well-prepared soil . It performs well in wet areas or even shallowly flooded fields .
Climate Preferences
For successful germination, soil temperatures should be above 65°F . The plant thrives in full sunlight and is suited for soils with a pH range of 5.5 to 7.0 . It can handle both drought and waterlogged conditions, making it a resilient option .
Additional Perks
Reaching up to 4 feet tall in just 60 days, Japanese millet provides quick ground cover and excellent erosion control . It also attracts birds and serves as a nutrient-rich feed for poultry, offering calcium, protein, vitamins, minerals, and carbohydrates .
5. Sunn Hemp
Sunn hemp is a summer cover crop that works wonders for improving soil, even in challenging conditions.
How It Benefits the Soil
Sunn hemp is highly effective at fixing nitrogen and produces more biomass compared to many traditional cover crops . Here's a breakdown of its soil benefits:
| Benefit | Performance |
|---|---|
| Nitrogen fixation | Up to 300 lbs/acre |
| Weed suppression | Up to 90% |
| Biomass production | 20% higher than crimson clover |
| Nematode control | Excellent |
| Subsoil nutrient extraction | Very good |
Tips for Growing Sunn Hemp
Sow sunn hemp seeds ¼ to 1 inch deep, using about ¼ lb per 250 sq ft in home gardens . While seeds can germinate at 48°F, warmer soil ensures better growth .
"Sunn hemp is known for its nitrogen-fixing abilities, making it an excellent choice for enriching soil fertility." – Southern Exposure Seed Exchange
For the best results, treat the seeds with a cowpea-type Rhizobium inoculant to boost nitrogen production. However, growers in South Florida have reported success without it . Keep the soil consistently moist for the first two weeks after germination .
Ideal Weather Conditions
Sunn hemp thrives in a wide range of conditions, growing well in soils with a pH between 5.0 and 8.5. It performs best in temperatures above 68°F and is highly drought-tolerant, making it perfect for hot, dry summers .
Additional Benefits for the Garden
Beyond soil improvement, sunn hemp offers other advantages. It can reduce wind speed and protect crops like papaya from virus damage . For optimal results, terminate it after 60–90 days to prevent shading nearby plants . An added bonus? Sunn hemp doubles as a nutritious feed for livestock, making it a great choice for integrated farming systems .
Conclusion
Summer green manures are a powerful tool for improving soil health and nutrient cycling. They are well-known for enhancing soil structure, fertility, and biological activity, making them an excellent choice for gardeners aiming to enrich their soil.
Different types of green manures offer specific benefits depending on your garden's needs. Here's a quick reference to help you choose the right one for your soil:
| Soil Condition | Recommended Green Manure | Key Benefits |
|---|---|---|
| Poor, compacted soil | Sorghum‐sudangrass | Breaks up hard soil and adds organic matter |
| Low fertility | Sunn Hemp | Fixes nitrogen effectively |
| Well‐drained | Buckwheat | Grows quickly and provides excellent cover |
The success of green manures depends on timing and local conditions. For colder areas, plant warm-season options like buckwheat or sunn hemp in spring. In warmer climates, summer planting works well if irrigation is available .
"When in doubt, throw the seed out." - Ea Murphy, Dirt Secrets
This quote highlights the importance of generous and timely seeding. For example, in New York, a poorly performing onion field was rejuvenated within a year by planting dense sorghum-sudangrass, restoring it to the quality of a freshly cleared field .
Homeowners can also seek guidance from Thrive Lot experts to incorporate green manures into their garden plans. Their work has transformed over 1.25 million square feet of yard space while saving nearly 12 million gallons of water .
For the best results, focus on proper seeding and termination practices. These steps are key to cultivating a thriving garden throughout the summer.
