Spring is a week old and cover crops in kitchen garden beds need turning soon, but what I really need to do right now is make a planting plan for 2021. Beans and peas, beets, carrots and fennel, cucumbers and squashes, spring turnips and radishes, corn are still in seed packets, and tomatoes, peppers and eggplant, onions, lettuce, broccoli and cauliflower are growing indoors in pots and flats. Where will I plant each vegetable this year?

I have a paper layout of all the kitchen garden beds, twenty-one of them arranged in three groups of seven, each bed divided vertically into three sections for recording three years of planting.  I also have a table where I’ve recorded what’s grown in the beds each year since 2001. It should be an easy process of looking at what I’ve planted in each bed for the previous three or more years, selecting the appropriate vegetable for that bed this year and entering it on the piece of tracing paper I place over the garden bed layout.  Quick to describe, but not so quick to carry out.  

Crop rotation is what gardening books and websites call the process I’m puzzling over as I make a planting plan. It’s the practice of planting vegetables in different beds or rows each year.  Three reasons for crop rotation are to discourage insects that may have overwintered in the soil and could feast on the same plant again, to minimize build-up of diseases plants may leave in the soil over time and to improve soil fertility by alternating plants that take a lot from the soil with plants that return nutrients.   

I know why I should rotate vegetables from bed to bed or row to row, but how I should carry it out is a yearly puzzle with lots of pieces.  Fortunately, there are many excellent websites on crop rotation providing charts grouping all the vegetables I grow into their respective families and reminding me which families help each other and which don’t so much.  

The Washington State University Snohomish County Extension Fact Sheet on Crop Rotation in Home Gardens is a helpful two-page document that defines crop rotation, describes why it is important, and explains how to do it. It also has an easy-to-use chart separating vegetables into their families and a printer-friendly version. 

Seattle Tilth offers a short description of crop rotation that includes a useful sentence alerting gardeners to the disease susceptibility of several plant families: 

Certain plant families are especially susceptible to specific diseases, including the cabbages (broccoli, cabbage, kale, and many more), the nightshades (tomatoes, eggplants, peppers, potatoes), and the onions (leek and garlic).

These are the families that I pay particular attention to when I’m making each year’s planting plan. I do my best to avoid planting members of the same family in beds where other members of the family have grown in the past two or three years, but one vegetable requires me to modify the rules: tomatoes.  I grow tomatoes every year in a greenhouse with permanent beds.  My solution to the diseases that tomatoes can leave in the soil is to swap the dirt in the greenhouse beds with dirt from beds in the garden, avoiding beds where other members of the nightshade family have grown. A couple of afternoons with the wheelbarrow accomplishes this task and has worked very well for the twenty years we’ve planted tomatoes in the greenhouse.  

A very useful site covering all aspects of crop rotation is Portland Nursery’s newsletter on crop rotation. In addition to describing the benefits of rotating vegetable crops and providing a list of vegetables and their families, it offers suggestions and sample plans for crop rotation in small year-round vegetable gardens.  It also includes cover crops as vegetables to include in crop rotations, useful for those of us who plant cover crops each fall. And in a side bar, it lists helpful rules for crop rotation.  

Portland Nursery’s Rules for Crop Rotation:

• Two growing seasons should pass before a plant family returns to soil it has already grown in.
• Heavy feeders such as brassicas, cucurbits, and solanums should follow light feeders (all others).
• Surface feeders such as corn should follow deep rooters like brassicas.
• When removing a finished crop, clean up thoroughly in that area, and leave no debris in which pests or diseases may overwinter.
• Keep records of what happens and use this information to help plan future plantings.

I especially appreciate the reminders that “heavy feeders should follow light feeders” and that “surface feeders should follow deep rooters.”  And it’s always good to be reminded to tidy up and keep good records, on-going aspirations of mine.

Finally, the site Harvest to Table written by a kitchen gardener in Sonoma Valley of California is useful even for those of us gardening farther north.

He’s more specific than the other sites about plant families and their effect on soil: 

Some crops are heavy feeders; heavy feeders include tomatoes, broccoli, cabbage, corn, eggplant, beets, lettuce, and other leafy crops.

Some crops are light feeders: light feeders include garlic, onions, peppers, potatoes, radishes, rutabagas, sweet potatoes, Swiss chard, and turnips.

Some crops are soil builders: soil builders include peas, beans, and cover crops such as clover.

And while he suggests that: “Simple crop rotation would plant heavy feeders in a dedicated planting bed the first year, followed by light feeders in the same bed the second year, followed by soil builders the third year,”he acknowledges that not all gardeners have the space to rotate crops so tidily and offers suggestions for working in smaller garden spaces.

Last, as an alternative to thinking about crop rotation by vegetable family, this author suggests crop rotation by harvest group, an intriguing way to think about the rotation process. 

Crop rotation by harvest groups is a simple rotation strategy: rotate leafy crops, root crops, and fruiting crops. Harvest group rotation is not a precise crop rotation method (for example, peppers are light feeders and tomatoes are heavy feeders, but both are fruiting crops—but it is an easy way to group plants and to remember the rotation from one year to the next. A simple three-year crop rotation divides crops into their harvest groups:

Leafy crops—lettuce, spinach and members of the cabbage family such as broccoli, Brussels sprouts, cauliflower

Root crops: carrots, turnips, parsnips, potatoes

Fruiting crops (flowering crops): tomatoes, peppers, eggplants, cucumbers, squash

In another entry, he writes in detail about the more traditional crop rotation by plant family.

After reviewing all this crop rotation information, I’m heading back to my planting plan, more confident than before that I can keep all the plant families getting along for another year.