A Bay Weekly reader called asking when to cut back asparagus tops.
To maximize next year’s crop and to get early production of sprouts, delay cutting back the tops of asparagus plants until after they have turned completely yellow. You want all the nitrogen in the stems and foliage to migrate back to the roots in the ground.
As the chlorophyll in the stems and leaves breaks down, the tissues turn yellow. What is occurring within the stem is migration of the nitrogen in the foliage down to the roots. Nitrogen is the only element in plants that remains mobile. All other elements remain fixed and are retained in the cells to be released only after decomposition.
Many years ago I reviewed a research paper that demonstrated the importance of delaying the removal of asparagus tops in the fall until after all of the stems had turned yellow. Cutting green stems not only delayed the emergence of new sprouts in the spring but also reduced yields.
The nitrogen drains from the stems and accumulates near the buds that will sprout the following spring. Only the area surrounding the buds accumulated the nitrogen. The tissues between the buds did not indicate any increase in nitrogen.
This process also occurs in deciduous trees. Fall foliage colors are caused by the degradation of chlorophyll. The nitrogen in the chlorophyll drains out of each leaf and accumulates around the vegetative bud visible at the base of the leaf.
After I cut back my asparagus, I like to mulch the bed lightly with about an inch of compost. I make another application of compost after I have finished cutting asparagus for the season.
Grubs Will Get Your Hostas
A: Over the weekend, I removed decaying, double-shredded hardwood mulch — I agree with you that this mulch is definitely not for low-maintenance use; it breaks down too quickly — from a shrub bed. My plan was to divide hostas. I found an unusual amount of white, wormy-looking insects bedded into the soil surface. I believe them to be grubs. They appeared to be in hibernation because when removed from the soil surface they began to expand in size and crawl. I’ve never treated the shrub beds for grubs. I always treat the lawn for grubs; however, I didn’t do it this year. Should this concern me?
–Larry Woodburn: [email protected]
Q: If the grubs have gray heads, they are June beetles. If the heads are brown, they are Japanese beetles. Either way, if you don’t kill them now, they will dig deeper into the ground, and next spring they will move close to the surface and eat some hosta roots before they emerge as beetles. I would kill as many as I could ASAP.