Crop rotation: or, why can’t I just plant tomatoes in the same spot every year??

As we’re getting into mid summer, some of the early season crops in the garden are coming into the last days of their productivity. Things like lettuce and peas have come to the end of their season and rather than leave those areas of the garden unproductive, we want to remove those plants and put in something else, that way we can grow as much food as possible in our small space. It’s important, however, to put in a new crop that will not deplete the same nutrients as the previous crop. For example, lettuce and spinach are both heavy nitrogen feeders, so it is best not to plant them one after the other. A better solution would be to plant a crop such as beans or peas, which return nitrogen to the soil in between, or to plant a crop that feeds less heavily, to allow the nitrogen to rebuild in the soil through adding compost.  A good crop rotation schedule will see heavy feeders followed by heavy givers, then by light feeders, and back to heavy feeders again. This can be done on a yearly basis for long season crops or throughout the season if you are practicing succession planting (growing more than one crop a year in the same space). A simple guideline to remember is that leafy and fruit crops tend to be heavy feeders, while root crops are lighter feeders. Rotating between these kinds of crops is also important because shallow rooted crops take nutrients from a different level of soil than deeply rooted ones do, and rotation allows both levels the time to rebuild nutrient levels.

Heavy Feeders: swiss chard, broccoli, cauliflower, kale , celery, corn, asparagus, cucumbers, melons, pumpkins, artichoke, lettuce, eggplant, peppers, and tomatoes

Light Feeders: beets, radishes, turnips, carrots, parsley, sweet potatoes, potatoes

Heavy Givers: beans, peas, alfalfa

Nutrient cycling is not the only reason to practice crop rotation. Moving crops around in your garden is also one of the best ways to prevent pest infestation. This is because after feeding on a crop, many pests lay eggs that overwinter in the soil. If the same crop is planted again in that location, the eggs hatch in spring and are presented with the tender leaves of their favourite crop, ready to be devoured! Crop rotation means that pests which overwinter will have to search for their preferred crop in the spring, giving your new plants a chance to establish and reducing the strength of the attack. For this reason it’s important to know the different families to which plants belong (see below). The Colorado Potato beetle will attack potatoes and eggplants, both members of the Nightshade family, so rotating them will not be an effective pest deterrent. Following eggplants with green beans and then carrots, however, would be a much better approach to deter pests, and will fortify the soil at the same time. Crop rotation must of course keep in mind the space and light requirements of each plant, and so certain crops, like sun-loving tomatoes can’t go just anywhere. Just do the best you can, and try to keep the principles of pest reduction and nutrient retention in mind when planning your garden!

• Onion Family (Amaryllis Family, Amaryllidaceae): Garlic, onions, leeks, shallots.

• Cabbage Family (Brassica, Cruciferae): Broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, cress, kale, kohlrabi, radishes, turnips.

• Lettuce Family (Composite, Daisy Family, Asteraceae): Artichokes, chicory, endive, lettuce.

• Beet Family (Goosefoot Family, Chenopodiaceae): Beets, spinach, Swiss chard.

• Grass Family (Graminae): Grains–corn, oats, rye, wheat.

• Bean Family (Legume, Leguminosae): Beans and peas, clover, vetch.

• Tomato Family (Nightshade Family, Solanaceae): Eggplant, peppers, tomatoes, potatoes.

• Squash Family (Cucurbitaceae): Cucumbers, melons, summer and winter squash, pumpkins, watermelon.

• Carrot Family (Umbellifer Family, Umbelliferae): Carrots, celery, anise, coriander, dill, fennel, parsley.