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The Flower Show

A Guide to Fall Cover Crops and Their Importance

September 07, 2023

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cover crops

By Sally McCabe, PHS Associate Director of Community Education

Let’s face it — summer is unofficially over, and all the newbies and amateur gardeners finished planting crops months ago. But what the pros know is that it's time to plan for fall harvest, rip out all the waning summer vegetables, and go crazy filling in all the spaces with cover crops. 

What are Cover Crops? 

Cover crops are exactly what the name says: crops that cover. They cover the ground with lush growth in all the nooks and crannies where nothing else is growing. But the difference between these and your normal fall plantings is this: we don't expect to harvest these to eat, sell, or give away. These are meant to stay in all winter, covering the ground as mulch and delivering several useful benefits. 

Why Use Cover Crops? 

If cover crops do all this, how come so few people use them? Many gardeners don’t want to admit that the summer is over, and all those green tomatoes aren’t going to miraculously turn red in the garden by the time frost hits. Most city dwellers don't have acres of available land, so we jealously guard every square inch, gardening intensively to get the most out of our limited space. It takes a shift in thinking to know when to cut our losses when we see diminishing returns on our summer crops. There are lots of compromises we can make along the way to make cover cropping fit our gardening style, including filling every available space in September and October, even between existing plants, while you're waiting for them to freeze or otherwise give up the ghost of new produce. 

What Can Cover Crops Do for Your Garden? 

Cover crops are very effective at preventing soil erosion and loss of valuable topsoil by protecting it from wind and rain. They also compete with weeds for sunlight, water, and nutrients -- reducing weed growth, while also trapping and holding excess nutrients. Cover crops add organic matter to your soil, which improves structure and soil fertility, and they attract beneficial insects, reducing the need for chemical pesticides. Some types of cover crops (in the legume or bean family) can even pull nitrogen from the air and fix it in the soil for upcoming crops. 

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Cover crops are meant to stay in all winter, covering the ground as mulch.

Choosing the Best Cover Crops for Your Garden

Choose cover crops that fit well into the available space without overcrowding or competing with your main crops. Gardeners should also select cover crops that can grow and thrive during the times you're not growing your main crops, like fall and winter. Additionally, determine your primary goal for using cover crops. If you need to boost soil fertility, plant cover crops like clover or hairy vetch to fix nitrogen. If weed suppression is your main aim, go for more aggressive cover crops like buckwheat. 

Below is some additional insight from PHS’s community gardens team on the best cover crops for your garden.  

“For small gardens, crimson clover and annual ryegrass are my favorite cover crops for the fall. Although I do like under-seeding brassicas in the fall with white clover as well, since it stays shorter than crimson. Annual Ryegrass is probably the easiest for beginners, and about 90% of all the cover crops planted on PA farms are ryegrass. Buckwheat is my favorite for sneaking in a cover crop during the season. White clover can stick around if you don't properly kill and incorporate it in the spring, but I don't think the others are a problem. Vetch may be an issue if you let it flower and seed.” -- Adam Hill, PHS City Harvest 

“We used tillage radishes [Daikon-type radishes penetrate deeply to break up and aerate hard soils].  Radishes were convenient for when we wanted extra winter veggies; they winterkilled easily and left the soil quite workable afterwards.” – Marta Lynch, PHS Norristown Farm Park 

For small intensive gardens, timing is also crucial when using cover crops. Here in Philly, sow your cover crop/s between September 15 and October 15 to maximize their benefit/s and allow enough time for decomposition before spring.  

With these tips and best practices in mind for cover cropping, you’ll be set up for success as you plan your fall garden. 

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