Hello Ruth,

I live in East TN and will be digging sweet potatoes in my home garden by the first frost which usually comes in the third week in October. The sweet potatoes are in a 500 square foot area. I am new to cover cropping and have experimented with oats, Australian pea and buckwheat. I am trying to decide which cover crop to plant where the potatoes were. It will be too late for the above mentioned. I found info that suggests winter rye but I also learned that it will tie up nitrogen. I also want to be sure that I can get rid of a crop come spring and it won’t be aggressive. Can you help guide me on this question?

Thank you and love reading your articles,
Nancy Gray

Dear Nancy,

Bravo. Sounds like you will be eating lots of delicious sweet potatoes this fall and winter! Your cover crop choice depends partly on what you want to do with that particular garden spot next spring. First, let’s go over a few cover crop basics.

source: pender.ces.ncsu

Bottom line? Never leave your garden soil bare. Why? You want to prevent topsoil loss, minimize soil erosion, and control weeds. You can mulch the area, or plant a cover crop. If you ignore this simple rule, nature will happily assist you in planting the area (with weed seeds). Cover crops can reserve and build nutrients over the winter, provide weed control, improve soil structure, break up compacted soil, and draw up nutrients from deep in the soil. They act as a green manure if turned into the soil or they can be utilized as a living or dead mulch. Cover crops also capture fertilizer that you applied last season and the crops did not use. Nitrogen, in particular, will wash out in winter rains and then be out of reach for spring crops. The cover crop acts as a nitrogen/ nutrient bank account. It takes the nutrients up into the plant over winter and reserves them – the nutrients are then returned to the soil the following spring when the cover crop is turned into the soil.

Cover crops generally fall into one of two groups: grains and legumes – and a mix of the two is often planted to reap the benefits of both. When a mix is planted, the grain acts as a support for the legume. If there is no available nitrogen in the soil, legumes will actually produce their own nitrogen, along with organic matter, that will benefit subsequent crops after they are incorporated back into the soil. Grains have good biomass, and will uptake and reserve nitrogen as they grow and re-release it back to the ground after they are turned in. Mustard, turnips, giant radish, and rape (canola) are also used as winter cover crops.

In the fall prepare and mulch one small area so it is readily available for very early spring planting. Mulching avoids the need to incorporate the cover crop, which takes a while and may be delayed if the spring is wet. For the remaining areas, choose a cover crop that suits your planting schedule and crop rotation plan. In garden areas that will be planted in early spring you could combine oats or barley with a legume (these grains will sometimes winter-kill making them easy to incorporate) Rye – which is harder to kill and incorporate until it has set seed – is better suited to later crops and combines well with a legume. The longer you let your cover crop grow in spring, the more biomass and potential nitrogen you will have accumulated to benefit your soil.

COMMON GRAINS for WINTER COVER

• -Winter Rye (grain) – rye can prevent weeds seeds (good) and garden seeds (bad) from germinating during its initial stages of decomposition
• -Annual Rye (grass)
• -Winter Wheat
• -Oats – 2.5 lb/1000 sq. ft., can winter-kill
• -Barley – spring barley winter-kills reliably at 17 degrees, but the seed is harder to find locally, a Pat Battle favorite

LEGUME COVER CROPS – Use the proper inoculant to improve nitrogen fixation

• Austrian Winter Peas – a personal favorite, the edible pea tips are delicious
• -Crimson Cover – annual and looks beautiful
• -Red Clover – perennial for a couple of years
• -White Clover – a low growing perennial
• -Sweet Clover – annual or biennial
• -Hairy Vetch
• -Fenugreek – reliably winter-kills, a Pat Battle favorite

Here is a great link to detailed descriptions of each cover crop.

The buckwheat you discussed is a summer cover crop, however oats and peas can be planted now. Rye can be sown very late – probably into December – as it will germinate in temperatures as low as 34 degrees. Even though it may not be perfect timing, local farmer Pat Battle and I both felt that most winter cover crops could still be sown now and even later. Ideally they would have been planted earlier, but they will still come up and grow now – and then really take off in late winter/early spring. Pat strongly recommended using an inoculant with the proper Rhizobium bacteria on your legumes (there is one for peas and a different one for clovers) to increase your nitrogen fixation. He also mentioned that Wren Abruzzi Rye is easier to incorporate in the spring than regular winter rye.

One of my favorite combos is Austrian Winter Peas and Oats and it is easier to incorporate than a rye cover – especially if the oats winterkill. (Pat Battle said that oats only seem to winterkill in years that you don’t want them to!). One of Pat’s many favorites is a barley/fenugreek combination because both reliably winter-kill. Rye and crimson clover are another great combo, especially for areas where you will be planting later crops. I have never planted hairy vetch for fear that it would become an established weed, but lots of people like it. Because it is perennial, white clover would mostly be used as a permanent mulch in the pathways or in a spot you will not be planting for a number of years. All the clovers are wonderful pollinator forage and encourage the presence of beneficial insects.

In my garden, I scatter the larger seed first (like winter peas) and rake it in, and then scatter the smaller seed (in this case oats) and rake them in. If I were planting Rye and clover, I would seed the rye first and then the clover – because clover is a very tiny seed that I just tamp in with the back of my hoe.

Cover crops are usually cut down one to two weeks before you intend to plant your spring crop. Two weeks is needed for the cover biomass to start breaking down, avoiding nitrogen competition with your crops. The longer you wait to cut the cover crop down, the bigger it will be (meaning more organic matter or biomass) and the more nitrogen the crop will have accumulated. Incorporating your cover crop into the soil will be easier if you wait a few days after cutting it down to turn it into the ground. Freshly cut cover crops will get tangled up in your tiller. Many people strip away only enough soil to plant their crop and leave the cover crop in place as a mulch. Some farmers use a seed drill (it is a big piece of equipment) to drill the seed right in amongst the cover crop – utilizing no-till methods.

Farmers often use special equipment, like flail mowers, to deal with cutting cover crops down. On a garden scale, the fastest way to cut down a cover crop is with a weed eater. If you don’t want a weed eater flinging your cover crop in all directions, you can use a scythe or hedge trimmers. Very small areas of cover crop could even be cut down with scissors or with a kitchen knife (be careful!)

In summary, never leave your ground bare. Anytime you are not actively growing food, consider planting a cover crop to grow (improve) your soil. Choose the appropriate cover crop for your spring planting plan. Every addition of organic matter is improving your soil in numerous ways. Give it a try and let us know how it turns out!

Enjoy your sweet potatoes,
Ruth

Local Seed Sources:

• Fifth Season
• Reems Creek Nursery
• Sow True Seed
• Southern States
• Villagers

Other Seed Sources:

• Johnny’s
• High Mowing
• Peaceful Vally Farm Supply
• Seven Springs Farm

*Make sure seed you order is not treated with an insecticide/fungicide

Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School

Author: Ruth Gonzalez

Ruth Gonzalez is a former market farmer, gardener, and local food advocate who wants to see organic farms proliferate and organic gardens in every yard. She also served on the Organic Growers School Board of Directors. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.