Gardening Harmful insects Plant diseases Vegetables

Family Ties Help Determine Crop Rotation

Illustration showing 4 vegetables rotating.

When planning crop rotation in the home garden, you need to know the family ties of your veggies and herbs. Illus.: Claire Tourigny

Crop rotation is an age-old cultural practice that involves never growing the same vegetable, or even a vegetable from the same plant family, in the same place two years in a row as a means of reducing disease and insect infestations. 

For example, always growing tomatoes in the same spot year after year would be looking for trouble. That’s because most tomato disease spores (and tomato are just about the most disease-prone vegetables, aren’t they?) overwinter in the soil at the base of their host plant. When you replant tomatoes in the same place the following year, the disease is already there, ready to attack. But if you plant your tomatoes elsewhere, the spores will not be able to easily reach them. And that’s the basis of crop rotation.

So, rotating your tomatoes is a great start, but since peppers are from the same family as tomatoes (Solanaceae) and are prone to many of the same diseases, peppers should not be planted in that spot either. Nor should eggplants, nor ground cherries, also in the Solanaceae family. 

The same goes for all other vegetables. Try to rotate your vegetables not just by species, but by family.

Illustration showing vegetables rotating around a confused insect.
Rotating helps confuse pest insects. Illus.: Claire Tourigny

The same applies to insects: most overwinter, as eggs, pupae or larvae, at the foot of their preferred host. Except … insects are more mobile than spores. If they can’t find their preferred host nearby, they’ll go looking for it. This is doubly true if they overwinter as pupae, as they give rise to winged adults right away. At least overwintering eggs give larvae that are not as mobile.

Floating row cover placed over fennel.
By combining crop rotation with the use of floating row cover, you can readily exclude most common insect pests. Photo: http://www.gardensalive.com

Better yet when it comes to insect control, crop rotation can be combined with the use of an insect barrier, such as floating row cover, and thus conquer even flying insects. You plant the vegetable in a new spot where there are no eggs, pupae or larvae, cover it with an appropriate barrier and how could the insect get to it? (Read The Perfect Insect Barrier! to better understand how this works.) A simple two-year rotation can suffice in such a case: an insect that doesn’t find its host one year will die out and won’t leave any offspring for the following year!

In an ideal world, you’d stick to a 4-year crop rotation for the vast majority of vegetables, especially because of longevity of diseases, as some spores can survive dormant in the soil for several years. However, it isn’t easy to carry out a 4-year rotation in a small home vegetable plot where plants are all planted in very close association. So, if you’re stuck, even a 2-year crop rotation is better than none!

No Need to Rotate Permanent Vegetables

Not all vegetables need to be rotated. Rhubarb and asparagus, for example, are not grown like other vegetables. Unlike tomatoes and beans that you start from seed every year and can easily rotate, they’re permanent (or at least live decades). So, just plant them and leave them be.

Vegetables Classed by Plant Family

To help you plan crop rotation in your vegetable garden, here is a list of the main plants grown in temperate climate vegetable gardens (i.e., vegetables, herbs and certain small fruits) classified according to their botanical family.

Aizoaceae

New Zealand spinach

Apiaceae (Umbellifers)

Angelica
Anis
Carrot
Celery
Celeriac
Chervil
Coriander (cilantro) 
Fennel
Parsnip

Amaranthaceae (including Chenopodiaceae)

Amaranth
Beet (beetroot) 
Orach
Quinoa
Spinach
Strawberry spinach
Swiss chard 

Amaryllidaceae

Garlic
Leek
Onion
Shallot

Asparagaceae

Asparagus

Asteraceae (Compositae)

Artichoke
Cardon
Chamomile
Chicory
Dandelion
Endive
Jerusalem artichoke
Lettuce
Salsify
Tarragon

Boraginaceae

Borage

Brassicaceae (Crucifers)

Broccoli
Brussels sprouts
Cabbage
Cauliflower
Cress
Kale
Kohlrabi
Radish
Rocket
Rutabaga
Turnip

Caprifoliaceae (Valerianaceae)

Corn salad

Convolvulaceae (Morning Glory Family)

Sweet potato

Cucurbitaceae (Cucurbits)

Cucamelon
Cucumber
Melon
Pumpkin
Squash
Watermelon 

Fabaceae (Legumes)

Bean
Broad bean
Chickpea
Lentil
Pea
Peanut
Soybean

Lamiaceae (Mint Family)

Basil
Lavender
Lemon balm
Marjoram
Mint
Oregano
Rosemary
Sage
Savory
Thyme

Poaceae (Grasses)

Corn
Millet
Oats
Rice
Rye
Sorghum
Wheat

Polygonaceae

Rhubarb
Sorrel

Rosaceae (Rose Family)

Raspberry 
Strawberry

Solanaceae

Eggplant (aubergine) 
Ground cherry
Pepper
Potato
Tobacco
Tomatillo

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “Family Ties Help Determine Crop Rotation

  1. Hey, I just wrote about this, but in regard to nutrient depletion and replenishment. Soil borne disease and insects are not as much of a problem here as they are in other regions. I can grow summer squash in the same spot for quite a while, but not beans. In my former garden, I would have always grown beans on the (disdainful) fence if I could have. Seriously, there were times when I grew beans on the fence anyway, just for a bit of shabby but green vegetation.

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