Ask a Master Gardener

Frequently asked questions about cool-season vegetables


Which varieties of asparagus can tolerate heat?

Some of the "West Coast" varieties such as 'Atlas' and 'UC 157' are more heat tolerant (85 degrees) than the Jersey varieties (e.g., 'Jersey Knight', 'Jersey Gem'). However, they may be subject to winter injury in central and northern Missouri. Also, they don't perform well in high humidity environments. In general, the West Coast varieties do not yield as well as the Jersey varieties.

When should asparagus be harvested?

A limited harvest of asparagus can be made the second year after planting (one-year old) crowns for about 2 weeks or until the spear starts getting small in diameter. You must be careful not to overharvest asparagus. Asparagus should be harvested when the spears are 6 to 8 inches in length and the tips are still tight.

Is it better to cut or snap asparagus when harvesting?

Asparagus spears can be cut 1 to 2 inches below the soil with a knife or snapped with your hands. Many growers prefer to snap since it is faster. Also, snapping breaks the spear at the point where it is less fibrous.

Should I use salt to control weeds in asparagus?

Asparagus can tolerate salt, but it does not promote healthy asparagus growth. I do not recommend applying salt to asparagus for weed control. There is a risk of salt accumulation in the soil, and salt can reduce infiltration of rainwater and potentially leach on other soil, damaging border plants.


What causes beets to develop tops (leaves) but not roots?

Beet "seeds" are actually fruits that contain several tiny seeds. Thus, beets need to be thinned early (2 inches tall) to one plant per inch. Failure to thin makes the beets too crowded, prohibiting root formation. Also, planting beets too late in the season so that the weather turns hot can restrict beet formation.

Can beet tops be eaten?

Yes. Beet tops can be harvested when young and eaten as greens. There are some cultivars of beets that are specifically developed for greens production. They include 'Green Top Bunching' or 'Crosby Egyptian'.

Are all beets round?

No. There are some cultivars that are cylinder-shaped. 'Formanova' is a cylindrical beet that can be grown successfully in Missouri.


What can be done to prevent cabbage heads from splitting?

Splitting is caused by pressure of excessive water taken up after the heads are solid. Cutting the roots (spading on two sides of the plant) or breaking the roots (lifting and twisting the head to one side) can reduce splitting, but it also damages the plant and requires that the head be harvested relatively soon. Some cultivars are less susceptible to splitting.

My cabbage failed to produce a head. Why?

Cabbage will not form a head if it is planted too late (and exposed to high temperatures), underfertilized or drought stressed.

I have noticed small white to cream-colored butterflies flying around my cabbage plants. What are they?

These are the adult stage of the imported cabbage worms looking for a place to lay eggs. The eggs hatch and begin to feed on leaves.

How do I control worms in my cabbage and broccoli?

Use a lightweight row cover to exclude moths and prevent them from laying eggs. Using a Bt (Bacillus thuringiensis) insecticide such as Javelin, Dipel, Thuricide, Biobit, Agree and Xentari will effectively control worms and conserve beneficial insects. Begin application when worms are small. You may want to apply a couple drops of liquid detergent per gallon to aid in spray coverage.


Why don't my carrot seeds germinate?

It takes about 3 weeks for carrot seed to germinate and emerge from the soil. Do not plant carrot seeds deeper than 1/4 inch.

Why do carrots develop a "forked" shape.

Carrots need a loose, friable soil to develop a good shape. Forking is caused by anything that impedes root growth. This includes nematodes, stones, or heavy, compacted soil.

Why are my carrots bitter and woody?

Carrots are a cool-season vegetable. When daily high temperatures exceed 80 degrees, carrot color and taste will diminish.

What causes bitter, green tops on carrot roots?

Exposure of the roots to sunlight will cause the roots to get sunburned. The green color is the plant pigment chlorophyll. Hill soil around the shoulders of the carrot roots to prevent exposure to the sun.

(Source: Dr. David Trinklein, MU Extension; Original author: R.R. Rothenberger)

Dhruba Dhakal, PhD is a University of Missouri Extension Horticulturist, serving to Missourians about a decade in Central Missouri. Dhruba can be contacted at [email protected] with gardening questions.