Tuesday, January 24, 2012

Crop Rotation in Small Space Gardens

If, like us, you are working on your food garden plan for 2012, you are probably confronting the perennial problem of crop rotation. The smaller your food growing space, the more difficult it becomes to avoid growing the same crop family in the same soil year after year.
Corn needs a lot of space, and can be a challenge
to accomodate in a small garden.
Crop rotation is one of the best organic means of controlling vegetable pests and diseases and of avoiding severe depletion of soil nutrients.

For crop rotation purposes, it is helpful to sort the popular vegetables into their respective botanical families:
  • Potato Family--potatoes, tomatoes, peppers, eggplant, tomatilloes
  • Squash Family--cucumbers, squashes, melons
  • Cabbage Family--broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, kale, kohlrabi, mustards, radish, turnip, watercress
  • Carrot Family--carrots, celery, chervil, cilantro, dill, parsley, parsnips
  • Onion Family--garlic, leeks, onions, scallions, shallots
  • Pea Family--beans, English peas, snap peas, snow peas, Southern peas, soybeans
  • Goosefoot Family--beets, spinach, Swiss chard
  • Daisy Family--endives, lettuce
  • Grass Family--corn
  • Hibiscus Family--okra
  • Morning Glory Family--sweet potatoes
The last three, corn, okra and sweet potatoes, need a lot of space, and are among the most difficult to accommodate in a small garden. Ideally, a given vegetable family should not occupy a given growing space but once every five years. To accomplish this, you obviously need at laset five distinct growing spaces. If you plan on growing more than one member of a particular family, tomatoes and peppers, for example, you will need additional room. Where garden space is at a premium, this quickly becomes a serious problem. Here are some strategies we use to manage crop rotation.

First, note that the majority of popular vegetable varieties come from only six families. These are the ones that will cause you the most problems. From any one of these families, then, decide which crop you will need in greatest quantity. Assign that crop to your main growing space. Repeat with each of the remaining families until you run out of space.

Next, go back to your list and decide what crops can be "tucked in" here and there. For example, you can grow scallions in between cabbage or pea plants or parsley between tomatoes or peppers. Swiss chard is a good choice for having just a plant or two here and there, as are bush beans and lettuces. Various herbs can also be tucked in, and often will do double duty in repelling crop pests.

If you can grow some crops in containers, you can supplement your in-ground space. Containers are great for all the "tucked in" crops mentioned above. Other crops that perform well in containers are peppers, tomatoes, celery, eggplant, spinach, watercress and cucumbers (if trellised). Root crops, including radishes, carrots, leeks, and beets, can also be grown in containers if the soil is sufficiently deep. Potatoes grow well in containers approximating the size of a 30 gallon garbage can or larger.

Miscellaneous green crops, although not included in the list above, offer some other great choices for container growing. Arugula, corn salad, dandelion, miner's lettuce, mizuna, purslane, tatsoi, and "baby" varieties of bak choi will grow in a window box.

The advantage of using containers is that instead of crop rotation, you can practice "soil rotation." You can empty the container and add fresh growing mix, if necessary. You can also simply keep track of which crop grew in which container last season and grow something else in it this year.

Another strategy is to try to rejuvenate the soil in your growing spaces. This will be much easier if you grow in raised beds, but can also be accomplished for in-ground spaces. Replenishing plant nutrients and trace elements is relatively easy. All you need to do is dig in plenty of compost and other amendments. The challenge is doing something about soil-borne pests and diseases.

One of the best options for "pasteurizing" soil is solarization. Cover the growing area with a sheet of black plastic. You can buy it in rolls at DIY stores and many garden centers. Leave the plastic in place during a period of warm, sunny weather. The soil under the plastic will heat up, destroying insects and microorganisms and encouraging dormant weed seeds to sprout. This technique typically works best from late spring through fall, when the weather is most likely to be sunny. You can, for example, dig potatoes in June, solarize the bed for a week (assuming it doesn't rain) and then plant peppers in the same spot to harvest in September.

Finally, allowing a growing space to lie fallow for a season does not mean you cannot grow anything there. Using a vegetable growing space for herbs or annual flowers for all or part of the season makes great sense.

Please use the comments section to share your strategies for small space crop rotation.

Weekly Local Food Report
This availability of local fresh food continues to dwindle this week. I found oyster and shiitake mushrooms from Sevier County, acorn squash from Macon County, and sweet potatoes from Grainger County in the produce section. Plenty of preserved foods from local and regional producers remain available, along with fresh, local milk and eggs. It is apparent that Knoxville needs some enterprising growers who can produce more fresh veggies during winter. Working in our little greenhouses, however, it is easy to recognize the challenge this presents. Mainly, it is the absence of sunshine that makes growing even the hardiest crops difficult at this time of year. Without the solar energy, crops simply cannot grow, and supplemental lighting not only consumes electricity, but greatly increases production costs.

1 comment:

Erik said...

As a container gardener, this subject is near and dear for me. I've been getting more serious about tracking what was grown where over the last couple of years, as I have become unwilling to replace my soil as is generally advised in books. As you note, working in some compost and "pasteurizing" the soil are great options. Last year I also tried a beneficial bacteria product called Actinovate for fighting soil-borne diseases. My yields were pretty big last year and I lost no plants to disease, a challenge here in the northwest. Another great option that you didn't mention is green manure. Mache works great, with its delicate leaves that are very quick to decompose. Plus, the low temp that it germinates at allows the possibility of broadcasting seed in winter and growing enough to till it in before planting other crops. And if you use mache you can eat your fill and till in the rest. Great tips, John!