Rhubarb

Q. How do I harvest rhubarb? How long does it keep producing?

A. When the leaves have reached their peak of growth the outer ones first take a sharp clean knife and slice right through the stem at the soil line. Trim off the foliage tops and save only the ribs. The center leaves will be lighter green and not nearly as tall. Leave them to grow as they will pop along quickly by your removing the mature leaves. They were blocking the inside leaves and using a lot of the water and food.

Then when the new ones are mature trim them off. You should get about three clippings out of one plant. Be careful as the later ones when the temps start to climb tend to taste bitter.

It is a brief one shot harvest time but they come back year after year. I had one in Ohio that must have been 20 years old. Do keep watering the plants throughout the summer so that the root system will grow.

Q. What can you put on rhubarb or on the ground to keep away the insects that bite the side of the stalks?

A. These are the most common attackers of rhubarb:

Rhubarb Curcullio...
Chewing insect 1/2 to 3/4 inch long. Yellow dusted snout beetle. Adult beetles bore into stalks crowns and roots. Attacks wild dock (coarse weed). Burn all infested plants. Destroy wild dock in July after beetles lay their eggs.

See labels for rates:

Armyworms Cutworms...
Permethrin

Caterpillars that are 1 to 2 inches long...
Larvin
Mattch
Success
Confirm

Garden symphylan [Scutigerella immaculata]...
Small white centipede-like animals in the soil  
Telone II C-17 or C-35.

Gray garden slug [Agriolimax reticulatum]...
Feed on new leaf buds
Metaldehyde bait.                  
Follow label for proper rates.

Q. I am growing rhubarb in the San Francisco Bay Area where winters never get below 40F and summers are rarely hotter than 90F. The plant never dies. How and when do I divide the plant?

A. Rhubarb can propagated by planting pieces obtained by dividing the crown. Pieces are taken from 4-5 year old crowns. You can divide earlier if you desire more plants. Dividing can be done either in the spring or the fall with equal success but I have found early spring is best. Wait until early growth is just starting so you can see where to best divide the root mass. Dig up the crowns and roots being careful not to damage the crown. Cut the roots into 4-8 pieces. It is recommended to split dormant crowns between large buds or "eyes" so that at least a 2" cross section of storage root is left with each bud. Be careful not to break off the delicate buds otherwise the roots are quite tough and will tolerate quite a bit of rough handling. Very small buds will give small plants for the first few years after planting while 4-10 new roots can usually be obtained from crowns that have been grown a few years. Root pieces should be protected from drying or freezing if they are not to be planted immediately. When dividing crowns for replanting it is important to mark the vigorous plants in June and use them as planting stock the following spring. Crowns should not be divided from diseased plants.

You can divide rhubarb with equal success in either early spring or late fall.

Dig up the root ball being careful to not destroy too many roots.

For the first division simply use a shovel to cut through the root/rhizome cluster between the "buds" of new growth. Careful study of the cluster will reveal old rotten rhizome and roots. This is a good area to cut through.  Each new plant will have a small rhizome some roots and a "bud" of new growth because it is spring.

Before replanting the divisions examine the rhizome/root area for excessive rot and decay. If there is a significant amount discard this division. There will usually be some rot as this is part of the normal growth of the plant. Some old (10 years +) plants can have root masses that are 3' in diameter and 1' deep.

Plant in a mixture of garden soil and compost (50%). Rhubarbs like compost! Be sure to water well and check frequently. Cut off the largest leaves on divisions as they will only drain the strength from the plant and they will probably wilt and rot anyway. The new plant needs its strength for developing new roots.