Questions on: Radishes

Ron Smith, Horticulturist, NDSU Extension Service


Q: I have a question about horseradish. The roots, instead of being white, have brown streaks. The larger roots are partially gone and filled with brown scales that are turning soft and rotting, but the plant is not dying. The leaves are growing as usual. I would appreciate it if you would let me know what my problem is. (e-mail reference)

A: I'm sorry, but horseradish is something that I never have grown and consequently know very little about. I checked my herbal and vegetable references, but found nothing listed that addresses your problem. I'm sure a reader of the column will be able to answer your questions. When that happens, we'll forward the information to you.


Q: I am writing about my radishes. The last couple of years all I get is tops. I planted white globe, cherry and the red and white varieties. I planted some early in April and more in May. They all turned out the same. Out of three packages, I got four radishes. I was talking to some friends and they had the same problem. I used to have bowls of radishes to give away. (e-mail reference)

A: All top and little or no bulb growth is commonly caused by too much shade, seeding too thickly or planting in soils that have too much nitrogen and too little potassium. Radish plants need just the opposite, which is low nitrogen and high potassium.


Q: I have radishes that are flowering. Is there something wrong? I was told I might be giving them too much water. We also have very hard soil. I picked a few just to see if they were ready, but they weren't. Should I let them continue to grow or should I pull them? (e-mail reference)

A: Pull them out. They somehow received enough cold to cause them to go into their reproductive cycle. Once they have started to do that, they are not putting any energy into root development.


Q: Why can't I grow radishes? Our garden is rototilled every spring so it can't be that the soil is too heavy. Every year the tops grow well, but only two or three plants produce radish roots. I have talked with other gardeners in the area who also have the same experience. (E-mail reference, Moorhead, Minn.)

A: The most common cause for no radish root production is too high a nitrogen content in the soil. You may be using a fertilizer that is too high in nitrogen, resulting in great top growth but essentially nothing in the roots. If they are being grown in too much shade, root development will be either poor or non-existent. Other causes could be wireworm or root maggot infestation. I suggest trying to grow your radishes in another location. Make sure there is at least six hours of direct sunlight reaching the site.


Q: I have been wondering whether you planted sweet potatoes and if so what were your results. After your columns about sweet potatoes many people here tried them and reported that they had good results but that the potatoes got so large. I planted 14 plants and got 57 pounds. I know Gurney's Seed & Nursery is pleased with you as they sold a lot of plants to this area.

I also read that your radishes do not produce seed. I had some blooming at the time so I left them in the garden to see what they would do. They produced seed and for the past three weeks we have been harvesting the most wonderful radishes that have grown from the seeds. They are much better than spring radishes as the cool weather agrees with them.

As you can see, I like a gardening challenge. I am trying northern hardy peach trees at the present time. I will protect them like I do my roses. I hope to let you know in a couple of years that I have wonderful peaches. (e-mail)

A: Well, I'm glad to hear that everyone's sweet potatoes did so well. Mine produced lots of vine and enough sweet potato meat for one meal -- that's it! Of course they were under water for days a couple of times. This doesn't help crop production much!

Good luck with your peach experiment. I tried and failed -- the deer ate the whole two trees!


Q: Can you save seed for the next year from kohlrabi, turnips, radishes, carrots, rutabagas and bushbeans? Will inbreeding be a problem? I also would like some information on how to keep squirrels out of my garden. (Berkley, Mich.)

A: I've only saved seeds from beans and carrots before, and it didn't seem to be worth the effort on the biennial plants. But, if you would still like to, here is the information I was able to find.

For bush beans, which are annuals, you must allow the pods to reach full maturity and dry up. You can harvest the seeds in early fall/late summer from the dried pods. 

Carrots, which are biennials, take two growing seasons to get seeds. Store the carrots after the first season in a cool, dry place without their tops. Replant the root in the spring and it will send up a flowery stalk. This will set seed in late summer. Collect seed after it dries up.

Radishes, which are annuals, flower the same season, sending up a long flowering stalk—but I've never seen the seeds. 

For turnips, kohlrabi and rutabagas, which are biennials, you must dig up roots after the first year and replant the second year. They will then send up a flowering stalk the second year.

Use Ro-pel to keep squirrels out. Ro-pel is used to keep rodents away. Spray on your plants once a year, but make sure not to spray it on any edibles! Other things to try include hot pepper spray and cheap men's colognes.

Good luck and thanks for writing!


Q. Please could you tell me what is wrong with my garden soil? What can I put on it? My radishes come up nice and then they just turn into tops and no radishes. I have planted them thick, then I have planted them thin and still just have tops. Thank you. (Towner, N.D.)

A. Your problem sounds like the classic of too high a nitrogen content in the soil

Fertilizers for vegetable gardens should be higher in phosphorus than N. I suggest working in about 10 to 15 pounds of 5-10-5 per 1,000 square feet of garden.

Your radishes may also be getting too much shade. All vegetables should have at least six hours of direct sunlight. Thanks for writing.


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