Archive for April, 2012

Top Five Pros and Cons for Rye & Vetch Cover Crop in Veggie Gardens

Cereal rye and hairy vetch cover crop. Five feet tall 4/20/12

Not too long ago I was one of those people who knew a lot about plants but very little about soil.  I’d leave my veggie beds bare for the winter, not knowing what that meant.  After learning about soil’s needs, I started planting cover crops in 2011, and I’m so glad I did!

In late summer and fall of 2011, I planted cereal rye, a cool-season grass that makes rye grain, and vetch, a viney legume, in all of my veggie beds.  I inoculated the vetch seed with the nitrogen-fixing Rhizobium bacteria and then inoculated both with mycorrhizae.  Now it’s late April 2012, and it’s still alive and growing like crazy!

Here’s what I learned:

#1 Rye and Vetch Change Soil Drastically (PRO)

When I dug out bermuda grass (and a lot of trash) to make my veggie beds, the soil was dry, hard, and dusty.  I knew it would take a long time to reach the desired chocolate cake consistency – dark, moist, spongy, and smelling good and earthy.  With the rye and vetch cover crop, it’s almost there, and a huge difference from last summer!  The soil underneath the cover crop is very soft and spongy with beautiful aggregates.  This good structure will allow veggie roots to grow rapidly and air and water to percolate down into the root zone.

A great gardening goal is to always have something green and growing.  No bare soil!  Plants feed beneficial microbial soil life through root exudates.  As this cover crop was growing, it leaked a lot of sugary carbon compounds out of its roots to attract and feed microbes.  These bugs made the gums, glues, and gells that form soil into that chocolate cake consistency.  Bare soil has no living roots to maintain beneficial microbes at high populations through the winter.  Keeping soil life alive during the winter improves soil and ensures it’s ready to help veggie plants thrive in the spring.

#2 Plant-Available Nitrogen (PRO)

Nodules: Rhizobium bacteria fixing nitrogen on vetch roots. From http://ryansgarden.com

Instead of using synthetic nitrogen or expensive organic nitrogen inputs, why not grow vetch?  If inoculated with Rhizobium bacteria, the Rhizobium will fix nitrogen from the air and put it into nodules on vetch roots.  Isn’t that the coolest thing?  This handy cover crop reference says,

“Few legumes match hairy vetch for spring residue production or nitrogen contribution.  […] Hairy vetch delivers heavy contributions of mineralized N (readily available for the following cash crop).  It can provide sufficient N for many vegetable crops, partially replace N fertilizer for corn or cotton and increase cash crop efficiency for higher yield.”

That’s a whole lot of nitrogen!  And it comes at low expense with many other benefits.

#3 Weed Suppression and Free Straw Mulch (PRO)

Rye and vetch mulch drying down after cutting

No weeds here!  The cover crop’s outrageous growth in early spring smothers weeds by completely blocking sunlight.  I’m aiming for mostly no-till, so I’m cutting the rye and vetch off at its base.  This is generating a boatload of mulch!  Vetch mulch has a high nitrogen to carbon ratio, so it will decompose readily.  But rye straw at this late stage of growth (flowering seed head) has a lot of carbon, so it should last well into late summer.  This thick mulch will protect soil, keep soil temps cool in the summer so biology can thrive, hold in moisture, and prevent dirt splatter onto veggie plants.  And it’s free and organic!

#4 Beneficial Predators (PRO)

I’ve noticed a very big and diverse above-ground soil life community in the rye and vetch.  Loads of tiny mites, beetles, crickets, spiders, and ladybugs.  The diversity and populations are larger than I’ve ever seen in my garden.  The handy cover crop guide cited a study that showed a rye/hairy vetch mix sustained a population of aphid-eating predators that was six times that of unmowed volunteer weeds and 87 times that of mown grass and weeds.  I’ll take it!  Let’s get our predator populations really going and save ourselves loads of time this summer killing harmful bugs!

#5 Bad Timing for Early Veggies (CON)

Flowering cereal rye can be mow-killed.

Rye and vetch can be killed any time with herbicides, but organic gardeners must be patient.  Vetch can be killed organically when it flowers (late April/ early May in East Coast zone 7).  Cereal rye can be killed organically when it flowers around the same time.  (Flowering grain means the seed head is developing and the little stamens (anthers?) start to come out and drop pollen.)  Rye and vetch will die at this time by mowing or just knocking it down flat at its base.  No herbicides.

But you want to plant peas and lettuce and radishes in early March?  Whoops!  Not gonna happen unless you till in the cover crop or use herbicides, both of which I don’t want to do.  You can keep cutting it down at ground level, plant your peas, and then keep cutting the rye back, but rye REALLY wants to live at this stage and will stunt your early crops.  I tried it.  I did not try acetic acid sprays, which is another option.

This situation requires better planning in the fall.  I’ll need to designate beds for early spring veggies, and plant winter cover crops that will winter-kill (die on their own from hard freezes), such as oats and radishes.  But for later-planted summer crops like tomatoes and peppers, I’ll definitely plant rye and vetch again.

Seed Sources

If you don’t have a local source, search online for “rye and vetch seed for sale.”  High Mowing Seeds sells five pound batches for about $20, plenty for a 1,000 sq. ft. garden.  Think of all these benefits for such a low cost!  Thanks for reading!

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