Building your soil--what to do with cover crop

Nodules on a fava bean root

Plant life is just incredible. Some plants actually feed the soil while they grow. A cover crop, also called a "green manure", is a plant that fixes nitrogen in the soil. Actually, the plant doesn't fix the nitrogen, but bacteria which live in a symbiotic relationship with the roots do this. Nitrogen exists as a gas in the atmosphere, which is unavailable to plants. Some plants are able to absorb nitrogen from the air and store it in their roots on nodules. The nodules are white bulbous growths on the roots. The presence of nodules doesn't always mean fixation--cut them open, and if they're pink, they have fixed nitrogen.

Plants in the legume family, notably beans, peas, and clover, and also weeds like vetch will host nitrogen fixing bacteria. There may be other kinds of plants which do this too--some grasses like oats, may also help fix nitrogen. The bacteria usually are already present in the soil. But to be sure of their presence, you can first innoculate the seeds with the appropriate bacteria, available from a mail order farm supply store. The way cover crops work, you grow the plants from seed (innoculated or not), and when the plants have grown and are 50% in flower, you dig them into the soil. For less soil disturbance, you can simply cut them down, and mulch them in place. (Note: favas will resprout if the roots are not dug up)

For this reason, you probably don't want to grow super delicious snap peas to fix nitrogen--because you would destroy the plants before the peas form. My understanding is it's an "either/or" situation--either you eat the crop, or you dig it in to fix nitrogen. For this reason, most cover crops are things people don't tend to eat--some nurseries or seed companies sell a mix of bell beans, vetch, and some kind of oatstraw--all "weedy" things that grow well, but can be turned under without any regret. Fava beans are dual purpose, so you could grow some to eat, and turn under some also.


Farmers turn under the crop with a disk harrow (plough takes it too deep to do any good), but the small scale grower can just use a shovel. I cut the favas first , and then dig them in to the soil about 6 inches or less. (Children may enjoy doing this). There will still be some pieces above the ground, but the roots should be thoroughly disturbed, and most of the greenery buried. Then I cover the area with rice straw (I buy a bale from the local horse track, and let the chickens use it first), about 2 or 3 inches thick. It has to sit at least a month before you can plant into it. In a month, you won't see any greens, only dark rich soil.

Don't forget to water it in the meantime, as this enables the microbes to break it down!

Why I love Fava Beans

If I said potatoes were the easiest vegetables to grow, I misspoke--fava beans have got to be the easiest edible plant to grow. Or at least in the top ten. That's not the only reason why I love them. The other reasons are: they don't need to be staked, they like cold weather and aren't bothered by even a hard frost, they are beautiful plants with sweet smelling flowers which honeybees like, the leaves are edible raw in salads, the roots fix nitrogen in the soil--so growing them can improve your soil, and the beans are tasty. I also read that they can be used as a treatment for parkinson's disease--they have some chemical that is helpful, but check with your doctor before you try it.

The only downside to fava beans that I can see is that you have to peel the larger beans twice, which is a lot of work. But, you can eat the smaller beans pod and all, and I have made great stew with them--just add a little beef.

March is not the right time to plant fava beans in our zone (9b), because they don't like hot weather, it seems. But they would be a great thing to plant now in colder climates. Here, I plant them in the fall, and they grow all winter, where we get lows in the 30's. Now is the time of year when they are tall, flowering, beginning to produce beans.

I like to eat them, but I also grow them as a cover crop to improve the soil. If you grew them as a cover crop, now is the time to turn them under and mulch them. More about that another time.

Build a mini-greenhouse

pumpkins, beans, soy beans survive low 40's in a mini greenhouse

Why build a mini-greenhouse? Well, even if you have a sunny windowsill inside, chances are it only gets sun part of the day. If you're sprouting tomatoes or squash, which will be on the sill for a month or so until the nights are warm enough to be outside, they'll get "leggy". In other words, they won't have the amount of light they'd prefer, so they'll be stretching to reach the sun. Leggy starts don't look so good, although they'll do o.k. once in the ground. They will be weaker plants than those that get the light they need.

One solution is to buy a grow light station, with electric lights suspended over the seedlings. These can be expensive, but you can find inexpensive ones. It's a fine solution to the problem, although if you are like me perhaps you want to try to grow your food without the use of fossil fuels. (as much as possible--after all, I use plastic pots...)

A greenhouse gives the plant the light it needs, along with protection from the cold. Most people living in the city don't have the space for a greenhouse, and they can be costly. A mini-greenhouse is a plastic covered frame tall enough to accommodate young plants as they grow, and provide protection from the cold. It's easy to make one. Here's one I made out of old metal coat hangers and discarded plastic sheeting from the laminating machine at the school where I work.

You'll need: wire coat hangers, flexible wire to attach, wire cutters, pliers, plastic sheeting, heavy duty clear plastic tape, and some patience.

I used a planting tray to size the greenhouse. That way, once the pots are inside, the top will stay in place without any other secures. Shape the wire coat hangers with the pliers and attach them with the flexible wire. Cut the plastic sheeting to fit the frame, and tape it in place. (I did this one frame at a time). I put the top on a "hinge" made out of three pieces of flexible wire poked through the plastic sheeting, and attaching the cover to the body. An improvement to this design would be a way to fasten the cover to the body when closed--it stays closed if it isn't windy, but when the wind blows, the top comes open, which exposes the plants to the cold.

During the day, with temps in the high 50's or 60's, it's fine to have the top open--even desireable, since the inside can be 10 to 15 degrees warmer on a cloudy day. In the full sun, they might cook. At night, with the cover closed, the plants inside will stay in the 50's when outside temps are in the 40's. You do have to watch them to keep them moist, but they won't dry out as often as plants in the open do. Notice that the plants are not in airtight conditions, which would encourage mold.

The case for starting seeds

A happy pumpkin sprout

Starting vegetables from seed is not difficult, but does require some attention. I like to do it because I can grow what I want, it gives me a closer relationship to how the plant grows, and it's much cheaper than buying starts at the nursery. The main things to know about starting seeds is to use a good potting soil, plant the seeds the depth they want, and keep the soil consistently moist.

A good potting soil is one that is moist, has some drainage elements like vermiculite or sand, and is sterile. Unless you really know what you're doing, or you feel confident mixing your own potting soil, just get some at a nursery--I tend to buy the more expensive soil just because I know the seeds will do better in it. Cheap potting soil usually doesn't moisten evenly, has large chunky pieces, is difficult to work with, and generally isn't much of a deal in my opinion.

Planting the seeds the depth they want means don't plant them too deep! Too shallow can be a problem, too. Check the packet, if you bought the seeds in a packet. Otherwise, the general rule is that seeds are planted twice the depth of their diameter--so small seeds will be planted in a shallow hole, and large seeds will need a deeper hole. There are exceptions to this rule--some small seeds I don't even bury--lettuce, dill, poppies and anything with a seed barely visible I just pat into the soil surface. Brassicas like brocolli, collards, and kale, have tiny seeds, but like to be planted at a half inch depth.

Anything with a really large seed I usually plant directly into the soil--beans, peas, corn, pumpkins. Especially the first three will outgrow their little pot in a few weeks, so starting them in pots only buys you a short amount of time. Also, there are some plants that don't like to be transplanted--it can be done, but they lose some growing time, or may not make it. Carrots, sunflowers, cilantro, and beets are some that come to mind. They do best when directly planted in the garden.

March is a good time to start seeds--if you start seedlings of plants that prefer warm weather, you can get a jump on the season. Warm season crops are a good thing to start now from seed--put them inside on a sunny windowsill. Tomatoes, corn, peppers, summer squash, pumpkins and other winter squash. Especially this year, the tomatoes, peppers, and summer squash crops were damaged in Mexico, and the grocery had a letter explaining why the price of these three crops will be more expensive in the coming months. This is the year to grow those crops yourself, and save some money.

In our climate, zone 9b, many things can be started in pots and left out overnight this time of year. Lettuce, radishes, broccoli, and others in the brassica family (kale, kohl rabi, cabbage, etc.), bulbing fennel, amaranth, quinoa. (This is what I have sprouting right now). If you have a really hot summer, don't start brussels sprouts, or sugar snap peas, or any cold season crop that has a long growing season. In South Berkeley where I live, we have a lot of fog in the summer, and last summer I barely took off my sweater, so those rules may not apply for us.

Planting vegetables from seeds is a great activity to do with kids: they will have a great appreciation when eating, but even before then, watching the plants grow is great fun. The best part is watching the seeds sprout. This is the time when the plants need the most babying--they must not be allowed to dry out, so careful checking every day, and usually daily watering is necessary. It takes time, but pays off.

As you watch seeds sprout, you'll get the know the character of each type--the fuzziness of tomatoes, the bold nature of bean sprouts, the tall skinny onions bent double at first, the tiny lettuce sprouts that even in their first leaves show the color and pattern they will take on, the heart shaped radish sprouts, the cloverlike shape of brassicas. To sprout seeds is to witness the miracle of life itself. It reminds us we are a part of this thing we call "nature"--we influence it, we are present in it, we are connected to all those who have grown plants in the past, and all those who will grow them when we are gone. So, plant your seeds. It's not just salad you will grow.

Watermelon radishes

The first day of March, and the weather is cold, heading into another rainstorm. Meanwhile, inside there are a variety of little sprouts growing steadily, waiting for warmer weather ahead.

One of the easiest things to grow is radishes. They grow in any season here in the east bay, and in less than a month you can harvest your crop, which makes them perfect to grow with children.
This year I'm growing watermelon radishes, which are an Asian radish variety, green on the outside and pink on the inside, thus the name. They make a colorful addition to salads, and have a mild flavor.

It's easy to start the seeds inside. One benefit of starting your own seeds is you get to see how the sprouts look. All radishes, despite the variety, look similar as a sprout. Once you have grown them a few times, you'll recognize the sprouts anywhere you see them. When they get their second set of leaves, you can transplant them outside. If you don't have a space to grow them in the ground, you can grow them in a pot, as long as you have at least six inches of soil depth. The plants need to be at least an inch apart, but further than two inches apart is wasting space.

Radish leaves can be eaten if cooked--they would probably taste best stir fried, like a turnip green. I haven't tried them, but they are edible. Having grown radishes, I can recognize the adult leaves anywhere, and notice a number of types of wild radish--some are tiny and grow like weeds among lawns. Others are tall, with beautiful white or pink flowers that develop in the late Spring or early summer. These grow in fields and abandoned lots, and near the ocean. They grow at the Berkeley marina, where I've seen a man pick and eat the pods (seeds). When you grow radishes, you will begin to notice them everywhere, and they will become one of your friends.