Farm Horizons, August 2013
Crop rotation important in gardens, too
By Christine Schlueter
I recently took a course from Cornell University on crop rotation and how important it is in gardening and also organic gardening.
It is not too early to plan your garden plot for next year. It is easier if you look at your garden area now and note where crops are, then map it out on paper. You will always have a referenece as to what you planted where.
Crop rotation is a fundamental principle of organic gardening especially vegetable gardening.
It doesn’t apply to fruit trees or perennials, due to their botanical relationships and how long they live in a given place. But for annuals, rotation is a mainstay of garden planning.
What is rotation? Like the name implies, it involves moving the location of where a crop is grown in the garden from year to year. Rotation is based on plant families, not individual species, because many of the vegetable crops are closely related.
Here is list of the more common plant families:
Amaranthaceae: Ornamentals: Celosia (cockscomb) and Gomphrena (Globe amaranth). Vegetables: beets, Swiss chard (both Beta vulgaris); spinach; lamb’s quarters; goosefoot; pigweed; calaloo, grain amaranth.
Apiaceae (formerly Umbelliferae): Ornamentals: English ivy, Queen Anne’s Lace (wild carrot). Vegetables and herbs: Carrot; celery; dill; caraway; coriander; cumin; fennel; parsnip; parsley; anise; ginseng
Brassicaceae (formerly Cruciferae): Many well-known plants come from this family, as weeds, ornamentals, and food plants. Ornamentals: spider flower, wallflower; dame’s rocket; money plant; alyssum; rock cress. Vegetables: Brassica oleracea contains cabbage, kale, collards, broccoli, brussels sprouts, kohlrabi, cauliflower. Brassica rapa contains turnip, Chinese cabbage, bok choi, tat soi, and many other Asian greens. Canola (rapeseed); mustards both wild and cultivated; radishes; rutabagas; capers.
Cucurbitaceae: Vegetables: pumpkins; winter and summer squash; gourds and loofah gourds; cucumbers; melons and watermelons; chayote.
Fabaceae (formerly Leguminosae): Ornamentals: lupines; sweet peas; sensitive plants; wisteria; indigo; locust trees. Vegetables: all peas; beans; lentils; chickpeas; peanuts; clovers
Solanaceae: Ornamentals: Petunia; Nightshade. Vegetables: Potatoes: eggplant; peppers; tomatoes; tomatillos; husk cherries.
In order to rotate properly, you need to rotate between families, such as Alliums and Cucurbits and Brassicas. Rotating between broccoli, cabbage, and brussels sprouts, for example, is not rotating between families, since they are all related Brassicas.
For annual flowers, rotating is based less on plant families, because there are many plant families represented among flowers. It is more important to keep mind where you grow the same flowers every year, and keep it moving around
Why rotate your crops? There are three good reasons:
1. Disease Pressure
Prevention is the key to disease control in organic systems. One of the main methods of preventing disease is crop rotation. Since many plant diseases are common between several crops within a family, it is important to know the plant families.
For example, both early and late blight affect potatoes and tomatoes, both members of the Solanaceae family. Where you have planted potatoes one year, you should not plant tomatoes, potatoes, eggplant, or peppers there for at least three years.
2. Insect pest pressure
Insect pests have to go find their host plants. If a crop is planted in the same place two or more years in a row, its pests don’t have far to go to find supper the following year.
It may not seem far for an insect to go across the garden to find its new host. It may get there, true, but it might get eaten by a bird as it flies across the garden. Or it might get confused by the strong scent of basil it encounters on its way, and get lost. You want to make it as hard as possible for pests to find their hosts as possible, and rotation is part of that plan.
3. Nutrient demands
Crops take different nutrients out of the soil. For example, broccoli takes up calcium, corn uses up a lot of nitrogen, beans add nitrogen. Carrots go deep, lettuce is shallow-rooted.
If a crop is in the same place year after year, the nutrients it demands will become depleted there, possibly even if you are adding adequate compost every year.
By moving crops around, you mix up their demands on the soil, which increases the likelihood that the soil will not develop particular deficiencies in any one spot.
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