Crop rotation

by M. Arjoca, vegetalshapes.com

Crop rotation means to grow the same type of plants on the same bed for only a number of seasons. It's a method used by gardeners and farmers.

The plants belong to different families and generally the members of a certain family have common characteristics about food needs, growth conditions, pests and diseases. For example, the tomatoes and the peppers belong to the same family (Solanaceae) and have the tendency to consume the same substances from soil and to be attacked by the same pests (tomato hornworm – Manduca quinquemaculata). To avoid this and for a better pest control you can practice crop rotation.

If you grow in the first year tomatoes or peppers on a certain bed, the next year on that bed you grow spinach (Amaranthaceae) or beans (Leguminosae). This way, the pests which prefer the plants from a certain family (Solanaceae) will not have available their favorite food next year. So they disappear or reduce their number.

The advantages of this practice are:

The insects and the fungi use some plants as host, for food, for development or to complete their life circle. Growing some type of plants (carrots), on the same place for many years you offer the chance to increase the number of pests which attack that type of plants (carrot flies). But if you grow on the same place every year or every 2-3 years another type of plant (onion), you break the life circle of pests because they don't have available anymore their specific source of food. For example, the ergot (Claviceps purpurea) is a fungus that grows on rye and has toxic effects on humans and animals. Growing rye every year on the same place increases the chances for ergot to proliferate. Instead you can grow next year on that place sunflowers, then lettuce or beans and then beets, so the risk of ergot presence reduces.

If you grow in the first year on a certain bed potatoes and the next year you grow tomatoes or peppers which belong to the same plant family (Solanaceae) on the same place, you risk the tomatoes or the peppers to be attacked by pests which attacked the potatoes in the first year. For example, Colorado potato beetle prefers to feed and to lay his eggs on potatoes leaves, but if the potatoes are not available, he is content with tomatoes or peppers too.

Here are a table with different plant families:

Plant families

Family

    Common name

Allium

Onion, chives, leek, garlic

Amaranthaceae

Spinach, amaranth

Asteraceae

Lettuce, sunflower, dandelion, dahlia, calendula, tagetes, chicory, cornflowers, aster etc.

Brassicaceae

Cabbage, Brussels sprouts, cauliflower, broccoli, turnip, radishes, horseradish, mustard, garden cress, nasturtium, alyssum

Cucurbitaceae

Cucumbers, squashes, pumpkins, melons, watermelons, zucchini

Graminae

Wheat, barley, oat, rye, rice, corn, cane, bamboo

Lamiaceae

Basil, summer savory, mint, lemon balm, marjoram, oregano, rosemary, thyme, sage, lavender, catnip

Leguminosae

Beans, pea, soy, lentil, alfalfa, lupin

Solanaceae

Tomatoes, peppers, potatoes, eggplants, petunia, jasmine tobacco, physalis, datura, tobacco

Umbelliferae

Carrots, parsnip, celery, parsley, dill, lovage, coriander, fennel, caraway, anise, chervil

The plants which belong to the same family tend to absorb from soil the same substances. For example, the bean and the pea belong to the same family and tend to consume the same substances. So they are not good companion plants and it's not recommended to grow them one after another on the same place. Instead, with the help of nitrogen-fixing bacteria which live on their roots, the beans and peas provide this substance to the soil and it’s recommended that next year to grow on that bed big nitrogen consumers (Gramineae).

You can alternate the soy crop with the corn crop and the cotton, which depletes the soil, with the peanuts or the peas which enrich the soil.

In the area threatened by erosion, crop rotation is very important for reducing the water and wind effects and for keeping the soil steady. Corn crops can alternate soy crops and wheat crops can alternate bean crops, for example. The tillage is reduced or is missing and after harvest the plant residues are left on field. This way the rain effects and soil transport are reduced.

The crop rotation can be done having in mind also the roots depth. You alternate deep rooted plants with shallow rooted plants, so the absorption of  nutritional substances is done at all levels. Also, some plants need food in a larger quantity than others. For example, the celery and the tomatoes are big „consumers“, but the beans and the peas consume less. If you grow successive big consumers on the same bed the chances to deplete the soil are big. If you grow alternatively big consumers and light consumers you will keep some soil balance.

Here is a table with plants which consume more or less.

Consumers

Big consumers

Medium consumers

Light consumers

Potatoes

Onion

Bean

Cucumbers

Carrots

Pea

Tomatoes

Lettuce

Parsley

Celery

Peppers

Basil

Cabbage

Radishes

Mint

Leek

Spinach

Chives

Pumpkins 

Beet

Summer savory  

Crop rotation can be done every year, but generally is done every 2-3 years.

Rotation time

Name
Maximum period on the same bed

Cucumbers

2 years

Tomatoes

2 years

Pea

2 years

Carrots

2 years

Strawberries

3 years

Onion

3 years

Bean

3 years

Cabbage

3 years

Potatoes

8-10 years

Lettuce

8-10 years

Asparagus

8-10 years

Celery

Many years

Radishes

Many years

Rhubarb

Many years

Parsley, basil, mint, dill, summer savory

Many years

Some tips are useful for crop rotation:

Knowing the plant families you can make a plan like this:

Time
Bed I
Bed II
Bed III
Bed IV
Bed V
Year I

Solanaceae

Leguminosae

Umbelliferae

Amarathaceae  

Leguminosae

Year II

Allium

Cucurbitaceae

Leguminosae

Leguminosae

Solanaceae

Year III

Amaranthaceae

Brassicaceae

Solanaceae

Graminae

Allium

Year IV

Leguminosae

Solanaceae

Amaranthaceae

Umbelliferae

Cucurbitaceae  

Or more specific

Time
Bed I
Bed II
Bed III
Bed IV
Bed V
Year I

Tomatoes

Pea

Carrots

Spinach

Beans

Year II

Onion

Pumpkins

Pea

Beans

Tomatoes

Year III

Spinach

Radishes

Tomatoes

Corn

Onion

Year IV

Bean

Tomatoes

Spinach

Carrots

Pumpkins

Or you can make 4 plant categories: fruits (tomatoes, peppers etc), leaves (lettuce, spinach etc), roots (carrots, celery etc), legumes (beans, pea etc) and rotate them every year.

Time
Bed I
Bed II
Bed III
Bed IV
Year I

Fruits

Legumes

Leaves

Roots

Year II

Leaves

Fruits

Roots

Legumes

Year III

Roots

Leaves

Legumes

Fruits

Year IV

Legumes  

Roots

Fruits

Leaves