Radical Radish Report
Growing radishes was pioneered before the Roman empire; the name “radish” derived from “radix,” the Latin word for “root” (the Romans could wield a sword but weren’t really clever with names!).
Mustard and turnips are close relatives to the radish.
Growing radishes can be a colorful pastime. Colors range from red, pink, and white, to gray-black or yellow radishes, in varying sizes and shapes, the most popular being the red round radish.
When to Plant
Growing radishes in the early spring usually gives us our first crop of the year, or at least competing with leaf lettuce.
We can usually plant radishes around early to mid May and have them in salads by mid June.
Depending on the variety of radish, they mature anywhere from 25 to 45 days from when you plant them in your garden.
If you live in the Southern climates, you can plant by mid to late January. For continuous harvesting plant a new patch every 7 to 10 days.
In Northern climates, you can plant 2 to 3 weeks before the last frost and again in late August or early September for a fall crop.
Radishes can withstand some very heavy frosts.
Avoid planting in the summer as radishes are a cool weather crop and they will bolt (go to seed) rapidly in the summer’s heat.
Hot weather can also create bitter flavor and root hollows in radishes.
Some later maturing varieties, such as Icicle or French Breakfast, are able to withstand summer heat, so can be planted later in the spring for a summer harvesting.
Winter radish varieties take longer to mature than radishes planted in the spring, so planting them in mid-August is recommended.
Where to Plant
Radishes do well in an area that has at least 6 hours of sun daily, but some shade is OK in the afternoon too.
As mentioned above, radishes prefer cool weather, so some shade is OK if your weather is going to get too warm by harvest time.
Radishes, like most root crops, like well-drained soil. And like most root crops, they like the soil loosened deep enough for them to reach their roots deep into the soil.
Plant your radishes, if you are able to, in sandy soil that also has a good amount of organic matter. Adding compost will give you the needed organic matter.
Preparing Your Soil
Radish grow best in a soil with a pH balance in the range of 5.8 to 6.8, although the optimal range is 6.0 to 6.5.
Use a pH tester to check your soil’s pH balance. If it’s too alkaline (above 6.8), add enough sulphur to bring it down below that level.
If it’s too acidic (below 5.8), adding lime is the simplest way to raise the pH of your soil quickly.
Before planting radishes, rototill 2 to 4 inches of well-aged compost into the soil. This should give you most of the nutrients your radishes will need for their short growing season. A handful of bone meal also helps every couple of feet down the rows as well.
After tilling your soil, smooth it out, removing rocks, sticks, or other debris in preparation for planting.
Choosing The Right Seed Varieties for Your Area
There are radishes for every season. Check with your local garden store to find out which seeds are resistant to diseases in your area.
Also check with your local garden center to see which varieties are good for the times of year you want to harvest radishes.
Spring radishes typically are mature in 3 to 6 weeks, whereas winter radishes take about 8 to 10 weeks.
Large retailers like Lowes or Home Depot probably won’t have as knowledgeable employees as a smaller locally owned garden store, but that isn’t always the case. I’ve found some very knowledgeable employees at our local Home Depot, so just learn who you can trust and verify the information they give you regardless of the store, large or small. Cross reference with your county extension office if you get conflicting information.
Seeds and Germination
Radish seeds are good for around 4 years after you’ve purchased them.
Radishes prefer cooler weather, but are able to germinate in a very wide range of temps from 40° to 90°F.
The optimal temperature range, though, is a more moderate 50° to 75°F.
At these temps, the average time for your radishes to pop out of the ground is about 5 to 10 days, depending on the weather.
The soil needs to be moist throughout the life of your radishes. Usually this isn’t a problem as they grow so well in the spring which is usually a damp time of year in many areas.
The ideal weather for radishes from seeding to harvesting is damp and about 50° to 65°F.
Starting Radishes Indoors
Because radishes are such an easy crop to grow almost anywhere, it’s not necessary to plant indoors in the spring.
The only exception is if you don’t have an area for gardening, then you can plant a container garden.
Mix compost and sterile potting soil, both available at your garden center, half and half.
Lightly press the mix into your container, such as a terracotta pot or a 5 gallon bucket. If you use a bucket, make sure you drill enough holes in the bottom to allow water to drain properly.
Plant your seeds by broadcasting several seeds per square inch in the pot, then raking them in with a fork. Press the soil lightly to seal the seeds in and water lightly to make sure they seeds have enough moisture to germinate.
Using the above method, try to make sure the seeds are a half an inch to an inch in the soil.
Once the seedlings come up, thin to about 2 inches apart and 2 inches from the side of your container.
Planting Seeds Directly to Your Garden
As we’ve discussed previously, radish are a cold-hardy plant and can be planted well before the last frost. We usually plant around the first of May, which is a couple of weeks before the last average frost.
Last year we planted around the first of May, then had a surprise late frost around the end of May. The radishes were unaffected.
Mark your rows and make a small trench with an old spoon or a sharp-tipped trowel, no more than an inch deep. Make three or four rows 6 to 12 inches apart. For us that is plenty of radishes. I can only eat so many radishes a year!
Plant your seeds in the trenches about half an inch to an inch. Backfill the dirt over the seeds and tamp it down lightly to make sure the seeds have contact with as much soil as possible.
If the soil needs it, lightly water the newly planted seeds.
Growing Your Radishes Successfully Until Harvest Time
Once the radishes are out of the ground, you can thin them to around 2 inches apart. Winter radishes may need to be thinned closer 4 inches apart.
If your spring is damp, watering won’t be necessary, but if it’s a drier year, water as often as you need to to make sure the soil remains moist.
If you have trouble with birds snacking on your seedlings, use a floating row cover over your radishes to keep the feather varmints out of your radish patch.
Jenny’s Tip – When you’re growing radishes, spray your plants every couple of weeks with a liquid organic leaf spray fertilizer. We highly recommend Organic Garden Miracle. It naturally stimulates your garden plants to produce more plant sugar in the photosynthesis process. That in turn creates a more robust plant, more produce from your garden, and better and sweeter flavor. And they have a really good warranty!
Mulching and Weeding
A light mulching of straw or grass clippings around your radish plants can help to keep your soil cool and weed free.
Any weeds that you have around your growing radishes should be carefully pulled or cut off so the radishes don’t have to compete for nutrients.
Keeping the surface of the soil lightly cultivated, moist, and weed free will give your radishes the love they need to succeed.
Don’t hoe too close or too deep around radishes or any root crop as it will damage the roots and therefore the plants.
Depending on which varieties of radishes you are planting, watering requirements will vary.
Watering requirements will also vary from year to year. Last year we had a cool, damp spring and summer, so we watered much less than normal.
During hot weather, it’s a good idea to lay down an inch of water a couple times a week on your summer radish patch.
Spring radishes in our area rarely need water, but your area may be different. Just make sure the soil stays moist but not wet at least 6 inches down.
Vegetables need at least 1 inch of water from rainfall or irrigation each week during the growing season.
Sandier soil may need more frequent watering. Mulched soil may need less. It’s something you’ll develop a feel for over time.
As with most vegetables, drip irrigation is superior to overhead watering, but drip systems may be cost prohibitive for the backyard or hobby gardener.
If you use overhead watering like we do, water earlier in the day so your plants can dry out by noon or earlier if possible.
If your radishes get too hot and dry, it stresses them and they’ll bolt (go to seed). It may also cause your radishes to lose flavor and/or get hollow heart.
Light watering of radishes is almost useless. Make sure your water gets at least 6 inches into the soil.
Companion Planting and Rotation Considerations
Good companions for growing radishes include squash family members, peas, spinach, melons, lettuce, carrots, pole beans, beets, nasturtiums, and chervil.
Radish planted among broccoli measurably reduced flea beetle damage to broccoli as the beetles preferred the radish in one trial.
Beets are beneficial preceding radishes as they add minerals to the soil.
Pole beans, bush beans and peas fix nitrogen from the air into the soil which is beneficial to growing radish.
Radishes are reputed to repel cucumber beetles and rust flies which are pests of carrots and cucumbers.
Chervil and Nasturtiums are said to improve the flavor or radish and help them grow faster. I haven’t tried this one, so don’t blame me if it doesn’t work!).
Lettuce is said to benefit radishes by making them more juicy in the summertime; I haven’t tried this one either.
Radishes benefit Spinach by luring leaf miners away from the spinach. Radish roots are unaffected by leaf miner damage to its leaves.
Radishes don’t play well with turnips and potatoes.
Root crops like turnips and potatoes compete for nutrients with growing radishes and will reduce your crop yield.
Radishes can be planted with parsnips, carrots, parsley, squash, tomatoes, or cabbage family crops as they mature more quickly. This is called “intercropping,” and it will help conserve garden space if necessary.
Radishes should not be planted in the same location more than once every three or four years.
When to Harvest
When your radish roots are around 1 to 1-1/2 inches in diameter, they’re ready to harvest. You’ll see the “shoulder” of the radish pop up above the soil when they’re ready to harvest. If you don’t harvest within a day or two, the roots will become pithy, flavorless, and woody.
Spring radishes are ready to harvest around 3 to 5 weeks after seeding.
Summer radishes are varied in size and color and flavor, but should be harvested young to get the best quality radish.
If they get overripe, their best use is your compost heap to be recycled.
Winter radish need to be harvested at a larger size, and typically are “black,” white, or green.
Once you’ve pulled your radishes, wash them, cut the stems off about an inch above the root and put in plastic zip lock-type bags and keep in your fridge for up to 2 weeks.
Black winter radishes, Chinese, and Daikon radishes will store for up to 4 months at 32�F at 95% humidity in a dark cooler/reefer.
Some gardeners have reported having good luck burying their radishes in the soil of a root cellar for up to a month…haven’t tried that one myself as I can only ingest a few radishes a year.
As far as we know, you can’t freeze radishes successfully, nor do they successfully dehydrate.
Although we’ve not tried this, we’ve heard from some canning pros that you can pickle summer and winter radishes; maybe we’ll review that process next spring.
Preventative and Natural Solutions to Common Pests
Cabbage root maggots are a small-sized white-colored maggot that tunnels into your radish roots. They come from a fly that looks like a common housefly, but is a bit smaller.
These small maggots are difficult to detect as your plants won’t wilt unless it is very hot and your plants are heavily infested, which is not common.
However, the quality of your radish crop will be compromised.
Using row covers in the spring is one solution to keep the flies out, but you’ll need to put row covers on before your plants come up.
Dusting the area with diatomaceous earth has been very successful against maggots. Food grade diatomaceous earth, which is composed of powdered fossilized algae, possesses razor sharp edges which are innocuous to most animals but fatal to insects.
When insects such as slugs, thrips, fly maggots, aphids, grubs, caterpillars, or mites ingest diatomaceous earth, it punctures their guts and they die from dehydration.
Flea beetles are another garden pest that attack radish, among other garden produce.
These tiny beetles chew holes in leaves and stems of seedling which is when they’re most vulnerable, and can weaken or kill the plants.
Row covers are effective if they’re completely sealed with dirt or sandbags.
Check under your row covers to make sure you beat the beetles to your plants and to make sure the weeds aren’t choking your plants either.
Proper nutrition and watering also helps your plants resist flea beetles. Ridding the area of bindweed and wild mustard also helps.
One effective remedy for these beetles is powdering your plants with diatomaceous earth.
Forked Roots are often caused by rocky or heavy soil. Removing rocks, sticks, and debris and adding generous amounts of well-aged compost as well as sand to the area can alleviate this problem.
Occasionally you may have beautiful radishes with not much of a root bulb. Thinning your radishes when seedlings helps.
Excessive nitrogen can cause this issue also, but if you’re using well-composted manure and compost, this organic solution rarely causes over-nitrification.
A third cause might be that the weather got to hot for your plants which can suppress bulbing, or if they’re planted in too much shade.
If your radishes are too spicy or pithy, you may’ve waited too late to harvest them or the soil may have gotten too dry during hot weather.
Preventing these issues is easy. Make sure your plants get watered regularly and deeply so your soil stays moist, and don’t wait too long to harvest your bulbs.
Root Rots can be a problem with radishes if your soil doesn’t drain well. If there is too much moisture (read “wet”) in your soil, fungal diseases like root rot can wipe out your crop.
You can either improve your drainage by adding lots of organic matter to your soil or rotate your crop to a new area that does drain well.
Club root is when your roots get swollen and stubby and develop a type of “wet rot.” You may see your radishes’ leaves turn yellow and stay small.
If you raise your soil’s pH to 7.2, it can be effective in eliminating this issue. Rotate your plants next season to a new area.
Barry Brown is a 3rd generation organic gardeners who is passionate about a sustainable and natural lifestyle.