CHAMBERSBURG, Pa. — Are you looking for cover crops to fill a fallow period as small grains, snap beans, or other crops are harvested? Establishing cover crops in summer grants an opportunity to branch out beyond our fall-planted standby cover crops like cereal rye and winter wheat.
The Northeast Cover Crops Council has come up with a fantastic Species Selector Tool that can help you determine the best species for your specific location based on plant hardiness zone, soil type, crop rotation, and goals. The tool also provides information on growth traits, planting and termination information, cost, and additional helpful comments.
A list of viable summer cover crops for Pennsylvania is presented below. For more detailed information on any of the listed species, please visit the Species Selector Tool at https://covercrop.tools/species-selector
If your main goals include soil conservation, late summer through early fall weed suppression, or forage for livestock, choose fast-growing species that offer tons of biomass. Some of the best species for these goals are summer annual grasses that will die after frost, like:
Can grow in flooded soils and standing water
Adapted to soil with pH as low as 4.5.
Very responsive to nitrogen (can produce 1500-3500 lb/A biomass)
Prone to premature flowering if seeded late summer
Good smother crop at high seeding rate but may become weed if allowed to go to seed.
Shorter, finer-stemmed, lower-biomass option compared to sorghum-sudangrass or pearl millet
Does not mow-kill as well and may mature faster/reseed more easily than foxtail millet
Mix with cowpeas or soybeans to create a diverse summer mixture
Does best under hot conditions
Fast growing, moderately good smother crop
Tall varieties are very similar to sorghum-sudangrass (below) except slightly lower biomass potential (3000-7000 lb/A)
Has regrowth potential, particularly when mowed or grazed high
Improved forage types (BMR) and cover crop types (non-BMR) cultivars are available and vary widely
better on acid and droughty soils
No prussic acid forage toxicity; nitrates still a concern.
Mix with cowpea, sunflower, and sunn hemp for a diverse summer mix
Sorghum-sudangrass (also known as Sudex, Sudax):
Fast-grower that reaches 6-12 ft tall, great biomass potential (4000-8000 lb/A) in the presence of lots of soil N
Similar to Sudangrass (below)
Fast-grower with great biomass potential (4000-8000 lb/A) in the presence of lots of soil N
Excellent subsoiler with thicker roots than most grasses.
Excellent weed suppressor due to competition and allelopathy (caution if next crop is small-seeded)
Good forage, but prussic acid and nitrate content can be a problem; explore improved forage types
Regrows well after mowing or grazing
Slow dry down will limit dry hay production; chop or wrap for forage
Mix with cowpea, sunn hemp and sunflower for a diverse summer mix
High heat and drought tolerance.
Needs heat to grow well (200-5000 lb/A biomass).
Excellent weed suppressor, fine foliage leaves a clean field for a following crop.
Good for forage/hay.
Low risk of setting seed, so unlikely to become a volunteer problem
If your main goal is providing nitrogen for the next crop, consider the following legumes, making sure to inoculate each with the appropriate rhizobium species
Does not thrive on droughty soils due to shallow root system
High potential for biomass (1200-3000 lb/A) and N production (70-150 lb/A)
Works well in mixes with other species that winter-kill, especially grasses such as oats
Can be slow to establish but has potential to over-winter
Can be used for forage
Very heat and drought tolerant once established
Deep taproot, tolerates low fertility, and has some shade tolerance.
Good biomass and forage producer (2500-4500 lb/A) with high N fixation potential (70-150 lb/A)
Provides good weed suppression
Flowers are key for beneficial insects
Some suppression for problem nematodes
Low reseeding and weed risk
Many varieties available: use forage or cover crop cultivars, with bush types for short mixes, vine- or runner- types for tall mixes
Less predation by deer and woodchucks compared to soybeans
Soybean (also known as forage soybean)
Good N-fixation, biomass, and forage potential
Low reseeding and weed risk
Do not use in rotations where soybeans are grown as a cash crop to decrease disease, insect, and nematode buildup
Many varieties are available; use late-maturing or forage cultivars for high biomass
Bushy growth habit mixes better with short grasses like foxtail millet
Similar to cowpea for cover crop use
Attractive to deer so not recommended for areas with high deer pressure
Compared to cowpea: more tolerant of cool weather and wet soils; less tolerant of drought, pests, and poor soil fertility
Spring Pea (also known as Yellow Pea or Canadian Spring Pea)
Plant early for lush growth (1000-2500 lb/A biomass)
Fast-growing varieties are available.
Mixes well with upright cover crop species due to its vining growth habit
Lower biomass and total N fixation compared to overwintered peas and other fall-planted legumes
Good in grazing mixes
Can tolerate low fertility soils and has even been used in bioremediation efforts for soils contaminated with heavy metals
Establishes quickly, can produce great amounts of biomass (1000-8000 lb/A), and fix substantial amounts of N (60-120 lb/A)
Effectively suppresses root-knot nematodes
Low weed risk
Becomes stemmy as it matures
Certain cultivars contain alkaloids which are poisonous to livestock; check before feeding to animals
Spindly growth habit with narrow leaves seems to make it a better choice for mixes than in monoculture—mix with sorghum-sudangrass, pearl millet, and sunflower for a diverse warm season mixture
If you want a species to help suppress soil pests or want a nutritious and palatable addition to a forage mix, choose a brassica, but be aware that winterhardiness varies by variety, planting date, and weather:
Forage Radish (also known as Daikon or tillage radish):
Fastest-growing if good fertility is present; good for suppressing weeds (1200-3000 lb/A biomass)
Winter-killed residues decompose and release N rapidly
May overwinter if snow cover is present to buffer temperature extremes
Plant early and plant at the low end of the recommended seeding rate for large plants that are more likely to winter-kill
Good in mixes to add diversity, especially with peas and oats, but plant at the low end of the recommended seeding rate range to prevent it from out-competing companions
Plant in mix with a winter-hardy grass such as cereal rye if N leaching over winter/early spring is a concern
Excellent for grazing
Potential for fast fall growth, high biomass, good N scavenging with adequate residual soil fertility.
Cultivars can vary in bulb-vs.-leaf ratio, winter-hardiness, day-length response.
Big bulbs can be slow to break down, can interfere with subsequent operations like planting
Similar to radish/rapeseed, but much less taproot – instead makes bulb on surface
“Mustard” encompasses several species including white/yellow mustard (Sinapis alba), Indian/brown mustard (Brassica juncea), and black mustard (Brassica nigra)— winterhardiness varies by variety
Similar characteristics to other brassicas such as rapeseed/canola
Most used for insect and disease suppression and adding diversity to mixes
Best brassica for bio-fumigation (requires soil incorporation)
Potential for fast fall growth and high biomass (500-2000 lb/A) with good soil fertility
Well-documented for deep N scavenging in fall
Can be a good alternative to buckwheat for weed suppression – slower to flower
Host for insects of many related cash crop species used in vegetable crop production
Do not feed to livestock
If you’re after food for pollinators or want to pull up nutrients from deeper in the soil profile, try one of these more novelty species:
Summer annual—it will winter-kill in Pennsylvania
Low tolerance to drought or high heat
Prefers light to medium textured well drained soils
Can tolerate low pH (5.0)
Excellent weed suppressor at high planting rates due to very fast growth (1500-2500 lb/A biomass)
Fine root system good for topsoil conditioning, but not subsoiling
Can “unlock” soil phosphorus (P)
Flowers are excellent for pollinators and other beneficials
Very easy to kill
High risk of reseeding if overmature; kill or mow within 7-10 days after first bloom. Sets seed faster than all other covers
Do not feed to livestock
Black oilseed varieties are most grown for cover crops
Good heat and drought tolerance once established
Sunflower blooms are attractive to people, pollinators, and wildlife
Deep branched taproot, good for pulling up nutrients (but not necessarily subsoiling)
Moderate weed suppressor (200-5000 lb/A biomass)
Low seeding rate means low cost
Adaptable in mixes; it may grow tall in a tall mix, short in a short mix.
Make sure to consider potential herbicide residual issues, pest life cycles, termination strategies and timing, and cost when choosing a cover crop species or mixture.
Taking advantage of summer-planted cover crops can add diversity to your crop rotation, help hold or fix nitrogen for your next crop, suppress weeds, protect soil, provide pollinators or livestock food, and more. If you would like assistance navigating the Selection Tool or would like to talk through your cover cropping plan, reach out to your local Penn State Extension Educator Heidi Reed, firstname.lastname@example.org, 717-472-8108, NRCS Conservationist, or Conservation District Ag Specialist.
–Heidi Reed, Penn State Extension