Harvest is long past but now is the time asparagus and rhubarb plants build up needed reserves for the next year. Be sure to water during dry weather and keep plants free of weeds. Foliage should be left until all green is gone. It can then be removed or left for the winter to help collect snow. (Ward Upham)
Is rhubarb and asparagus that has been frosted safe to eat? Let’s look at each of these individually.
Rhubarb: A light frost will not harm rhubarb. However, if temperatures were cold enough to cause the rhubarb leaves to wilt or become limp then damage has been done and such leaves should be removed and discarded. Any new leaves that appear and are normal can be eaten.
Remember that the leaf blade of rhubarb is poisonous regardless of whether it suffered cold damage as it naturally contains oxalic acid. The leaf stalk is the edible portion of this plant. However, when leaves become frozen, the oxalic content of the stalks increases, making them dangerous to consume. You can find more information on rhubarb at: http://www.bookstore.ksre.ksu.edu/pubs/ep99.pdf
Asparagus: Asparagus does not contain poisonous substances but frost will cause the spear tips to wilt and give them an off flavor. Remove and discard any spears that show such damage. We also have a guide sheet on asparagus at: http://www.bookstore.ksre.ksu.edu/pubs/mf319.pdf (Ward Upham)
Rhubarb, like asparagus, is a perennial vegetable. It is harvested for the leaf stem, which is also called a petiole. Some years rhubarb will produce large, hollow-stemmed seedstalks that arise from the center of the plant. These should be broken or cut out as they appear so that energy will go into plant vigor rather than seed production. It will take several weeks for all the seedstalks to appear so be vigilant in removing them. Newer varieties of rhubarb are selected for vigor, bright red-colored stalks and less of a tendency to produce seedstalks than the older types. (Ward Upham)
Rhubarb is a perennial vegetable that can be a bit tricky to grow in Kansas. It is native to northern Asia (possibly Siberia) and so is adapted to cold winters and dry summers. However, it is susceptible to crown rot and should not be subjected to “wet feet” and therefore should be grown in a well-drained soil. The addition of organic matter can increase drainage as well as raise the soil level so that crown rot is less likely. Also, have a soil test done as rhubarb does best with a pH below 7.0.
Rhubarb should be planted from mid-March to early April in Kansas. Mix 5 to 10 pounds of well-rotted barnyard manure into the soil for each 10 square feet of bed before planting.
Rhubarb is propagated from crowns (root sections) that contain one or two buds. Plants should be spaced 2 to 3 feet apart in the row with 4 to 5 feet between rows. The crowns are planted shallow so that the buds are just one-half to 1 inch below the soil surface. Firm soil around the crowns and make sure they are not in a depression that holds water. Recommended varieties include Canada Red, Crimson Red, McDonald and Valentine.
Rhubarb needs rejuvenated at least every 5 to 10 years and should be dug and divided in the same time period as new plantings are established. Use a cleaver or axe to cut crowns into sections that each contains one or two buds. Plant as described above.
Newly transplanted rhubarb should not be harvested the first year so the plant can recover from the transplant process. Only a few stalks should be harvested the second year to allow the plant to continue to build up its energy reserves. The harvest season for plants that are three years or older usually lasts about 8 weeks. Harvest only the largest and best stalks by pulling them slightly to the side so that they break away from the plant. Never harvest over one-third of the leaf stalks at one time. Only the leaf stalk (petiole) is eaten as the leaf blade contains oxalic acid and is poisonous.
Mulches can be used to reduce moisture loss, prevent weed growth and provide winter protection. However, it should be pulled away in the spring to allow the soil to warm so that early growth is encouraged. (Ward Upham)
Video of the Week:
Ward Upham is the Kansas State Master Gardener Coordinator and runs the Horticulture Response Center. Other contributors include K-State Extension Specialists.