Organic Garden Planner: Rotation, Cover Crops, Soil

Organic garden planner: three plans to write down

Organic growing leans on planning more than on products. The federal organic crop standard says a producer must manage crop nutrients and soil fertility through rotations, cover crops, and the application of plant and animal materials. You do not need to be certified to borrow that list. It names the three plans a backyard planner should hold.

Organic soil is built months before the crop goes in.

Work through the three plans in this order.

1. Find your starting number. Most soil testing labs include an organic matter test in their basic soil test, says the University of Maryland Extension.
2. Draw the beds and write a plant family under each one.
3. Set a cover crop sowing date and a cut date.
4. Write a compost amount next to each bed.
5. Back-count any raw manure from the harvest date.

Rotation: four beds, four plant families

Iowa State Extension says not to plant vegetables from the same family in the same place for 3 to 4 years, or 5 or more if you can. Its rotation guide lists the big families. Tomatoes, peppers and potatoes are nightshades. Squash, cucumbers and melons are gourds. Broccoli, cabbage and kale are mustards. Beans and peas are legumes.

The same guide has a simple layout. Four raised beds let you move each family one bed along every year, so a family returns to a bed once every four years. The table below shows one way to run it.

The Iowa State guide also says to keep a garden log, draw a map, or take a photo, so you remember where each family grew. A rotation only works if next year's you can read this year's plan.

Rotation has limits. A University of Vermont Extension note says it cannot prevent airborne diseases such as downy mildew, or insect damage from pests that migrate into the area. A plan on paper helps, but it does not guarantee clean plants.

How many plants each family needs

A rotation grid needs a plant count to be useful. Virginia Cooperative Extension's planting guide lists plants per person per planting, and says children may need half the amount of an adult. Multiply by the number of adults in your house.

Virginia also says to grow more of a crop if you plan to can or freeze it. Use these counts to size each family's bed, then check the spacing in the guide against your bed.

Cover crops: the fall window is short

A cover crop is a plant you grow for the soil, not for the table. The University of Maryland Extension says the ideal sowing period for fall cover crops runs from August 15 to October 1. Its cover crop page says winter rye can be planted later in autumn than other options and that legumes such as crimson clover convert nitrogen from the air into a form plants can use.

A University of New Hampshire fact sheet gives dates by species. Crimson clover is best sown by August 30, and slower legumes such as hairy vetch or clovers no later than September 15. Winter rye can be sown as late as early October in the southern part of that state. These are northeastern dates, so ask your county office for yours.

In spring, Maryland says to cut cover crops in late April or early May before they set seed. Then leave about two weeks for the plants to break down before you plant vegetables. Put that gap on your calendar, or the first sowing will land in a half-rotted mat.

If your window has already closed, winter rye is the species the sources say can go in latest. A bed left bare this winter is a missed step, not a failure. Put next August's sowing date on the calendar now.

Soil: 1 inch of compost per bed per year

The University of Maryland Extension says the goal for vegetable beds should be 5 to 10 percent organic matter. Its soil amendment page says 1 inch of compost per year can help maintain garden productivity. It also notes that most soil testing labs include an organic matter test in their basic soil test, so you can find your starting number.

The sum is easy to do on paper. A 4 by 8 foot bed is 32 square feet. One inch is 1/12 of a foot, so 32 divided by 12 gives about 2.7 cubic feet of compost. A cubic yard holds 27 cubic feet, which makes 2.7 about one tenth of a yard. Four such beds need about 10.7 cubic feet a year.

Write the amount next to each bed on your plan. Then you can order the right quantity once and tick the beds off as you spread it.

Mulch and compost on the calendar

The University of Maryland Extension says compost, home-made or bought, can be added at any time of year and used as a top-dressing or mulch during the growing season. Leaves can be spread on beds to protect the soil over winter, then moved aside for planting in spring and put back as mulch. Wood ashes go on in fall or winter, and only based on a soil test.

On paper, that gives each bed three dated lines: compost, leaf mulch and any ashes.

Companion plants without sprays

Maryland's page on succession and companion planting says the volatile compounds of alliums, basil, rosemary, lavender, dill, cilantro and chives repel aphids and other insects or make it harder for them to find their host plants. It says African and French marigolds deter soil-dwelling nematodes, and that thyme, onion and nasturtium help reduce caterpillar damage in broccoli. It also says clusters of small flowers attract pollinators and the natural enemies of garden pests.

Treat these as helpers, not as spray replacements. The Vermont note above says rotation will not stop pests that migrate in, so a plan that relies on one trick can fail. Put a herb or flower row beside each bed on the map, and keep rotating.

Manure: count back from harvest

Raw manure carries a rule. The federal text says raw animal manure must be composted unless it goes on a crop not meant for people, or is worked into the soil at least 120 days before harvest when the edible part touches the soil, or at least 90 days before harvest when it does not.

Here is how to plan with it. Say you expect to pull carrots on August 1. Count back 120 days and the manure goes in by April 3. For a crop whose edible part stays off the ground, 90 days back from August 1 is May 3. The text leaves the judgment to you, so if you are unsure, use the longer interval.

Composted material has its own test. The standard describes a pile held between 131 and 170 degrees F for 15 days in a windrow, turned at least five times. Buy compost from a source that can say how it was made, or make your own with a thermometer.

Mistakes and mid-season fixes

Same family, same bed. Fix it with the garden log, map or photo that Iowa State recommends, taken at planting time.

A late cover crop. If the window has closed, sow winter rye, which Maryland and New Hampshire say can go in latest.

Manure too close to harvest. If the count-back puts the date in the past, add compost, which Maryland says can go on at any time, and use the manure in fall.

A skipped test. Most labs include the organic matter test in the basic soil test, so order one now and write the number on the plan.

When a rotation grid has nothing to rotate

If you grow in two containers or a single bed, a rotation grid has nothing to rotate. Keep a note of the family and the compost date, and skip the rest.

Check your state extension office too. Some publish a rotation chart or cover crop dates for your area, and a local sheet beats the northeastern dates above.

Free extension pages and charts exist, and everything above comes from them. A printed plan helps when several beds and four years have to fit on paper. The Garden Year bundle counts from your own last-frost date and has a freeze-date table for 108 NOAA stations, so it works in any US zone. Print it at 100 percent (actual size) so the bed grids keep their true scale.