My Radishes Don't Bulb

Wire Stem

• If no part of the plant is thriving, including the root, the most likely cause is wire stem, sometimes called damping off. The distinguishing characteristics of wire stem is a thinning and toughening of the stem of a plant at the surface of the soil. In radishes, wire stem causes the root to rot quickly or to not grow at all. Wire stem is caused by a fungus. To prevent it, plant radishes in in different place each year and make sure not to plant too early or in soggy soil.

Crowding

• Sometimes crowding can cause radish roots to be stunted. If crowding is the problem, you should see some full-size radishes on the ends of the rows or in places where there is less crowding. Radishes should be smallest where there is greater crowding. To prevent root stunting due to crowding, thin your radishes when they are seedlings to 1/2 to 1 inch apart.

Nitrogen

• A common cause of stunted radish bulbs is too much nitrogen. If you fertilize your radishes with a high-nitrogen fertilizer, the plant will spend all its resources growing leaves. If your radishes have had too much nitrogen, they will have beautiful, lush leaves and a skinny, almost nonexistent bulb. To prevent the problem, choose a fertilizer with higher levels of potassium and lower levels of nitrogen.

Potassium

• Another possible reason for small radish roots is too little potassium. Potassium is necessary for root development. If your soil is deficient, it can cause radishes that have normal tops and very little bulb. The best way to check the potassium level in your soil is to have your local extension service run a soil test. If you find you are low on potassium, you can supplement with small amounts of potash or other potassium-rich fertilizer.

Heat

• If you had a late spring, short spring or early summer, your radishes might be suffering from premature heat. Cool-weather varieties of radish grow best when the temperatures are below 65 degrees Fahrenheit. If you plant in cool weather and then the weather turns quickly hot, the radish will stop growing both leaves and roots and will go to seed. To prevent radishes from going to seed before they get a chance to develop a bulb, plant as soon as the soil can be worked in the spring.