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)
Asparagus is one of those vegetables where freshness is incredibly important. If you have never eaten asparagus fresh out of the garden, try it. It may convince you to grow some of your own. For those who have an asparagus patch, the new spears should be appearing soon. The first asparagus that comes through the ground always seems to take a long time to reach harvest size. That is because asparagus growth is temperature dependent. The higher the day and nighttime temperatures, the faster it grows. Also, the longer the spear, the quicker the growth. As the season progresses and spears get longer, the growth rate increases.
Harvest asparagus by snapping or cutting. Snapping is quick and easy. Simply bend the stalk near the base until it breaks. Snapped ends dry quickly so refrigerate or use soon after harvest. If you cut asparagus, use a sharp knife to detach the spears slightly below ground level. This base is woodier than snapped asparagus, so it doesn't lose water as quickly. Cut off woody ends before cooking. (Ward Upham)
If you haven’t removed last year’s growth from asparagus plants, now is the time. Asparagus comes up around the first of April in Manhattan but will be earlier in southern Kansas and a bit later further north.
Also, asparagus benefits from a fertilizer application early spring. Fertilize according to a soil test or add 1 to 2 pounds of a 10-20-10 fertilizer per 20 feet of row before growth starts. If a soil test shows that only nitrogen is needed, apply 1 pound of a 16-0-0 product or ½ pound of a 30-4-5, 27-3-3 or similar fertilizer per 20 feet of row. Incorporate lightly with a tiller or rake in fertilizer before spears emerge. Fertilize again at the same rate after the last harvest. (Ward Upham)
The best time to control weeds in asparagus is early spring before the asparagus emerges. A light tilling (or hoeing) that is shallow enough to avoid the crowns will eliminate existing weeds. Many gardeners like to mix in organic matter during the same operation.
Herbicides can be used before asparagus emerges. Glyphosate (Roundup, Killzall) will kill weeds that are actively growing, and the preemergence herbicide trifluralin can be used to kill weed seeds as they germinate. Trifluralin is found in several products, but not all of them list asparagus on the label. Those that do have asparagus on the label include Miracle-Gro Weed Preventer Granules and Monterey Vegetable and Ornamental Weeder. Mulch can also be used to keep weeds from invading.
No herbicides can be used during harvest. The end of harvest presents another opportunity. Remove all fern and spears and apply Roundup to control virtually all of the weeds present. Past the harvest season and after regrowth of the asparagus, options are limited. Products that contain sethoxydim can be applied to asparagus to kill grassy weeds. Sethoxydim has no effect on broadleaves including asparagus. Two sethoxydim products available to homeowners and
labeled for asparagus are Monterey Grass Getter and Hi-Yield Grass Killer. With broadleaves, the only option is to pull them and look forward to next year. (Ward Upham)
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Ward Upham is the Kansas State Master Gardener Coordinator and runs the Horticulture Response Center. Other contributors include K-State Extension Specialists.