When to Plant Radishes in Iowa: A Growers Guide

Radishes are attractive, easy-to-grow, and mostly edible vegetables that can be enjoyed as raw food or cooked into a tasty side dish. They have firm, crunchy flesh in various colors and unique shapes.

The seed pods are popular with birds (especially finches) because the radish seeds produce a small acorn-like nut with one of the most concentrated edible oil contents of any regular vegetable. This article takes an analytical approach to when you should plant radishes on your Iowa farm for maximum yield.

When To Plant Radishes In Iowa

When to Plant Radishes in Iowa

The best time to plant radishes in Iowa, according to an Iowa Master Gardener, is early spring when the soil temperatures have warmed a bit, and it is not too cold yet. The sooner you plant your radish seeds, as soon as the ground has thawed out after winter, the better your chances for success. You should typically expect to get about four weeks of germination from planting time.

November 15th – December 15th is when most gardeners start cultivating their crops in the western half of the state, and December 1st – February 28th is when people generally begin planting in central Iowa. Radishes need moist, loose soil with a pH level of 5.8-7.2, and they do not thrive well in poorly drained soils or heavy clay loam that retains water for long periods.

How To Plant Radishes In Iowa

When to Plant Radishes in Iowa

The following are three primary methods for planting radish seedlings.

i) Planting in Raised Beds

If you have raised garden beds, they are one of the easiest ways to plant radishes as they give each seedling plenty of room to stretch out and grow. We recommend tilling up the soil in your raised bed a few weeks before planting.

You can amend the loosened soil with compost or other nutrients to give your radishes a healthy head start. In addition, because raised beds are elevated off the ground, they are perfect for providing your seedlings with better drainage and extra protection from disease or pests. You should space the radish seeds approximately ¼ inch apart and inch into the soil (4 inches above ground level).

ii) Sow Radish Seeds

It is easiest to sow radish seeds directly in your garden beds then, but they do well all over the garden in rows spaced at least 12 inches apart. You can sow outdoors early in the spring (by April 15th is best) or start indoors a few weeks before your seeds and radishes need to be sown outside.

Sow the seeds by hand, one seed per hole/row, or you can use a tilling machine that will accomplish the same task. Though your radishes will sprout and grow into several large bushes, we recommend spacing them about 1 foot apart for most gardeners.

iii) Planting in Seed Trays

If you are starting to garden, you might consider starting your radishes indoors in a seed tray (a basic box with holes). That is especially helpful if you live in an extreme climate, where the weather may be too hot or too cold to start seeds outdoors immediately safely. You will want to sow your seeds directly into the soil, but make sure they do not touch or overlap each other. Once the plants are about 1-2 inches tall, they can be transplanted into larger pots or directly into your garden bed. Keep your radishes well-watered as they grow, and watch for pests.

When To Harvest Radishes In Iowa

When to Plant Radishes in Iowa

The easiest way to tell you are ready for the harvest is by looking for the radish tops growing back. They will have a tinge of white and be reasonably soft. If they have not grown back yet, wait until they are more swollen than the leaves and stems.

The ideal time to harvest is three weeks before the first frost in early fall. In particular, you can harvest the radishes 3-5 weeks after planting. You can periodically examine their growth by pulling 2 or 3 plants while approaching maturity. In most cases, it is advisable to harvest the radishes when their roots are appropriate one inch in diameter. Be careful not to leave too many radishes behind because their roots need full sunlight (or light shade) and drainage if you intend on storing them for winter use.

Challenges With Growing Radishes In Iowa

When to Plant Radishes in Iowa

Soil Types

The most common problem with radishes when gardening in Iowa is having too sandy soil. Radishes do not grow well in soils with a large amount of sand, as they cannot hold on to nutrients and moisture while growing. Instead, they require a good deal of moisture and nutrients to stay healthy and keep producing new radishes. It is best to use soil with more clay or loam than sand, though not necessarily clay, since the texture may be too dense for radish roots.


Radishes require plentiful amounts of water because they are sensitive to drought conditions. It is easy to over-water radishes in Iowa, so it is critical to use a soil moisture sensor to determine when the soil is moist enough.

Nitrogen Content

Radishes require a good amount of nitrogen, most often supplied by compost or manure. It is also critical that the soil’s nitrogen content around radishes is not excessive, as this can lead to a build-up of phytotoxins that inhibit root growth and prevent new radishes from forming.


Radishes are sensitive to cold temperatures, which means they can be damaged if temperatures drop below 50F for extended periods or are exposed to too much wind in the winter. That can lead to the production of pithy radishes that will not taste good and can even cause nausea in some people.

Fungal Disease

Radishes are vulnerable to several fungal diseases and pests such as are flea beetles, root maggots, and aphids. Therefore, you should treat them with a fungicide regularly, preferably after every few harvests. That will help prevent any fungal infections from spreading. And in case you do happen to get root rot, it is best to throw away all the plants immediately, so they do not spread the infection further.

When to Plant Radishes in Iowa: Final thoughts

Growing radishes takes a little bit of patience. You need to allow 18 weeks from when you plant your seedlings before harvesting your final product. Radishes are traditionally a cool-season crop, with the best production time between fall and spring in Iowa.

Plant them in full sun, with soil pH 6-7, and have been tilled to 8 inches deep and watered at least twice per week. Radishes are an excellent choice for new gardeners because they can be planted close together, germinate quickly, and tolerate less-than-perfect conditions. Radishes are also great for kids because of their fast growth, bright colors, quick harvest, and lack of thorns.

Related Article: When to Plant Tomatoes in Iowa?