Q: I’ve saved Dayle Davis’ wonderful May 2014 column on asparagus yet have a couple questions. She wrote “spears large enough to eat that are left in the garden to fern out provide a great site for asparagus beetles to lay eggs.” One question then is when allowing first and second year growth of crowns, what is the best way to protect against beetles?
My second question: this is the second summer allowing our crowns to develop and we have four clumps/plantings that are 9-feet tall with ferns sprawling everywhere. Can I prune back the ferns? If yes, how much?
A: These are great questions. For first- and second-year growth on crowns, it is especially important for spears to develop woody stalks and produce lots of healthy ferns/fronds. In a nutshell, energy produced by photosynthesis moves down the stalk to the asparagus crown in the soil for next year’s spear production.
Since photosynthesis takes place primarily in plant leaves, and almost none occurs in stems, those 9-foot-tall ferns in your garden are very important to the long-term success of your asparagus patch. Rather than prune them back, I suggestion that you run garden twine between tall stakes situated along the outside edges of the garden to hold the fronds upright and tidy their appearance as they carry on their vital, behind-the-scenes work.
About asparagus beetles: The adult beetles emerge in early spring after overwintering on old asparagus fronds or in garden debris. The adults then lay their eggs on the newly emerged spears. The eggs hatch about a week later and feed on the spears as young larvae. Some minor amount of asparagus beetle damage is to be expected and is usually not a problem unless 8 percent to 10 percent of the plants show evidence of larvae.
For first- and second-year growth of crowns, perhaps the gardener could choose to forego the traditional spring garden cleanup in favor of fall cleanup to minimize the possibility of overwintering asparagus beetle problems. Let me explain:
There are two schools of thought regarding overwintering of asparagus fronds. One is to maintain the dead fronds in place through the winter and remove them in early spring along with other overwintered garden debris in the asparagus patch. This practice is believed to afford an added layer of winter protection to the asparagus crowns and delay the start of spear production to a time when the chance of spring frost damage is minimal.
The other school of thought is to cut off at soil level and destroy all yellowed asparagus fronds during fall cleanup. This practice, along with clearing out all garden debris in fall, will help to keep garden pests, including asparagus beetles, from overwintering in the garden.
In subsequent years, after the asparagus patch is established, there are several ways to guard against asparagus beetles:
- Keep spears harvested to reduce the chance of asparagus beetles depositing their eggs.
- Hand pick adult beetles by knocking them into a container of soapy water.
- Use a cover of garden fabric to protect the asparagus until harvest ends.
- Forego spring cleanup; switch to fall cleanup of yellowed fronds and garden debris.
The harvesting season ends usually in late spring to early summer when emerging asparagus spears become skinny and spindly. Allow those spears to develop into the tall fern-like fronds described above. Inspect the foliage often. If you notice the stems turning brown, asparagus beetles are probably chewing on the ferns. Give these beetles the soapy water burial or spray the foliage with an approved insecticide.
For more information, call The Ohio State University Summit County Extension Hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3.
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to email@example.com, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.
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