Here’s a good article on crop rotation by Robin Sweetser for The Old Farmer’s Almanac.
WHAT IS CROP ROTATION? HOW DOES IT BENEFIT YOUR GARDEN?
If you grow tomatoes or other crops in the same garden bed year after year, you’re likely to notice an increase in pests and diseases. Break the cycle! Take a moment to learn about the basics of crop rotation. Your plants will thank you with a bigger, healthier harvest.
In the mad rush to get the garden planted in the spring, we forget all about something as important as crop rotation, which helps to slow the spread of garden pests and plant diseases. In the example of tomatoes, simply moving the tomato plants across the garden to where the squashes grew last year is enough to throw off those hornworms!
WHAT IS CROP ROTATION?
The concept of crop rotation is simple: It’s the practice of not planting the same crops in the same place in back-to-back years. By not planting the exact same vegetables in the exact same spot every year, you can avoid having pests and diseases continuously build up in the soil. If you move the crop, the pest or disease has no host on which to live. Ideally, rotate a vegetable (or vegetable family) so that it grows in a particular place once out of every 3 to 4 years.
For example, if you planted tomatoes in the same garden bed year after year, they’re more likely to be hit by the same pests or diseases that affected your tomato crop last year. So you’d want to plant them in a different bed in the following year. Then, in that first bed, you’d plant a different sort of crop such as carrots, broccoli, or chard. Finally, in the third year, you could plant tomatoes in their original spot again.
The purpose of crop rotation is not only to avoid pest problems, but to also consider the soil health and the nutrients that different plants need from the soil.
CROP ROTATION FAMILIES
The key to successful crop rotation is “all in the family.” Even though tomatoes, peppers, eggplant, and potatoes look nothing alike, they are kissing cousins in the same botanical family, the nightshades (Solanaceae).
Here are the major family groupings:
- Alliums: Onions, shallots, leeks, and garlic.
- Legumes: Green beans, green peas, southern peas, peanuts, soybeans. All legumes are soil “fixers” and share the benefit of adding nitrogen back to the soil.
- Brassicas: Broccoli, cauliflower, cabbage, kale, Brussels sprouts, turnip greens, radishes, collards, Chinese cabbage, mustard greens, and collards. Share pest issues and often need to be netted to block cabbage moths. Need nitrogen-rich soil. Plant after the legume (bean) family.
- Nightshades: Tomatoes, eggplant, peppers, and potatoes. All heavy feeders which need rich soil. Affected by the same diseases. Never follow tomatoes after potatoes.
- Umbellifers: Carrots, parsnips, fennel, parsley, and dill.
- Cucurbits: Zucchini and summer quash, cukes, pumpkins and winter squash, melons (watermelon, cantaloupe), and gourds. All heavy feeders that grow best in rich soil.
There are many more families, but some have only one member that we would grow in a home vegetable garden, like corn, okra, or sweet potatoes. In a small garden, you can group some families together, like putting brassicas with legumes and lettuce to make rotations easier.
There are exceptions to crop rotation; perennial vegetables and herbs shouldn’t be moved each year, since they stay in the ground year-round. For example, mint spreads easily and is often best contained to one bed, and asparagus needs to settle into a spot for several years before it’s ready to be harvested.
Lessen Disease and Insect Problems
Members of each family often suffer from the same pests and diseases, so planting a variety of crops from different families is a good way to lessen (or slow down) pest and disease damage.
For example, soil-borne diseases can build up after years of growing the same plants in the same place. Crop rotation might not cure all of your disease problems, but it can make a dent. As for insects, moving crops around can make it harder for overwintering pests to find their first meal come springtime.
Get to the Root of Crop Rotation
Crop rotation also benefits the health of soil, structurally speaking. Plants with different root lengths benefit the soil by aerating it in different ways. Deeply rooted crops such as tomatoes, carrots, or beets break up the soil, creating channels for air and water as they seek out minerals in the subsoil, bringing them up closer to the surface where other plants can use them next year.
Alternate Heavy and Light Feeders
Another aspect of crop rotation is alternating “heavy” feeders (plants that use a lot of nutrients) with “light” feeders (plants that use less nutrients) in order to reduce nutrient demands on your soil.
Heavy feeders, including corn, lettuce, broccoli, tomatoes, and cukes, require a lot of nitrogen to produce their flowers, fruit, and leaves. Give their beds a rest by planting carrots, potatoes, beets, or onions, which don’t need as much.
To add nitrogen naturally, plant legumes such as peas or beans, as they accumulate nitrogen-fixing bacteria on their roots. In the fall, don’t pull these plants up; clip them off and let the roots decay in the soil. They will leave behind nitrogen that is accessible to next year’s plants.
PLANNING CROP ROTATION IN YOUR GARDEN
Depending on the size of your garden, you can plan rotations that cover 3, 4, 5, 6 or more years, with 3 years being the minimum recommended.
As noted above, the best way to rotate annual vegetables is to group them by their plant family, since they are susceptible to the same pests and diseases and also have similar maintenance requirements. For instance, all plants in the cabbage family are best grown together, as this makes it easier to net them against cabbage moths and birds—and there’s no risk of accidentally passing on crop-specific soil-dwelling pests and diseases to the next crop.
A handy way to set crop order is to give each plant family a shade relating to the colors of the rainbow, as shown below. Using this order of rotation is optional, but it helps to make sure that the soil is in the correct condition for the following crop. The numbers listed in the diagram tell you
- Working from the inside of the rainbow out, you can see which plants belong together and which should come next in each bed. The rotation starts with lilacs and blues—onion family plants and peas/beans—which are commonly grown together as they both like soil enriched with compost and take up little space. Once you’ve harvested your onions and leeks from your first bed, the next crop in that spot would be cabbages, cauliflower and broccoli and so on, for the first seven categories.
- Plants in the Miscellaneous (grey) category are useful for plugging gaps in your beds, as they don’t tend to suffer badly from particular soil-borne pests and diseases, and can be fit in anywhere you have room, although it’s still a good idea to move them around from year to year as much as possible (particularly sweet corn, which can suffer from rootworm).
KEEPING A RECORD
Crop rotation is not as complicated as it sounds, but it can be hard to keep track of. Don’t rely on memory alone, particularly if you are growing different amounts of a variety of crops!
Just roughly sketch your garden and write down what you have planted where and by plant family. (It can also be helpful to keep a list of the variety names.)
EVEN EASIER: ONLINE TOOL!
This is where the online Garden Planner really shows its usefulness. Rather than having to remember a complete planning history of which vegetables were grown where over the past 3 to 5 years, and which family each vegetable belongs to, the tool just takes care of that for you.
Each plant icon is color-coded similar to the chart above so that you can quickly see at a glance which family it belongs to. When you plan a new season, it remembers what you have planted before and shows a red warning signal if you should avoid planting a vegetable in the area.
Bottom-line: The simplest rule is to grow your crops in different areas. Crop rotation is the best preventative medicine you can give to your garden!
A simple garden plan will be your best friend next year when it comes time to decide where those tomatoes should go.