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Fielding Questions: What's causing the holes in my hostas?

Gardening columnist Don Kinzler answers questions about holes in hostas, fall planting and more.

hosta with slug damage October 2022.jpeg
A reader asks gardening columnist Don Kinzler what may be causing holes in her hostas.
Contributed / Don Kinzler
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Q: My hostas get holes in them every year. Do you know why? – Dee V.

A: Although grasshoppers were a plague this summer, shredding leaves in many gardens, flowers, and fields, the damage to your hosta appears to be classic slug damage.

Slugs are best described as snails without shells. They’re slimy, soft, have no legs, and are usually brown or gray. They range in size from a quarter-inch to two inches or longer.

Slugs produce slime and use it to move, and their glistening slime trails can often be seen on sidewalks or other hard surfaces first thing in the morning. Slugs are usually active at night when the cool dampness allows them to crawl onto plant leaves, consuming holes in the centers of leaves as well as the edges.

By morning, slugs have moved for cover, hiding near the soil, safe under mulch, leaf debris, or other cool, moist spots. Because slugs are rarely seen actively feeding, unless you’re out in the yard with a flashlight in the middle of the night, the holes that appear in leaves are often a mystery to the homeowner.

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One way to monitor for slug activity is to wet the soil around the injured plant and lay a board or cardboard on the soil. The next day, check underneath the material, and you’ll often find slugs congregating.

Hosta are a prime target, because the shaded, moist environment enjoyed by the perennial is the ideal habitat for slugs.

Garden centers sell several products for slug control, including scratchy diatomaceous earth, copper bands, and baits containing iron phosphate, ferric sodium, or metaldehyde.

A method always mentioned is beer-filled trays sunk into soil at rim-level. Slugs reportedly crawl in and die. One might wonder, though, if the method would entice slugs to your yard from miles around for free refreshments.

Q: Can we put leaves and grass clippings in the garden this fall and roto-till them in, or is spring better? – Ed and Judy G.

A: Fall is a great time to add leaves, grass clippings, or any organic materials to vegetable gardens and flowerbeds, incorporating them into the soil by either digging or roto-tilling. By spring, much of the material will have decomposed, improving soil texture and workability.

Caution is needed when adding grass clippings, though. If lawns have been treated with weed killers, the clippings should not be added to the soil of gardens or flowerbeds. Many herbicides persist in grass clippings, sometimes for long periods, and if the clippings are added to garden soil, the herbicide residue can damage or kill future vegetables and flowers.

Q: I just bought some tulip bulbs that were on sale. Is it too late to plant them? – William M.

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A: Tulip bulbs can successfully be planted quite late in October, although the preferred time is September. Spring-flowering bulbs produce roots after planting, and earlier planting allows longer rooting time. Hyacinths and daffodils especially need a longer time to produce roots, so late planting is risky. Tulips, though, are more forgiving.

After planting the tulip bulbs, water the soil thoroughly. Because the planting date is later than desired, mulch the soil above the planting bed with twelve inches of leaves or straw. The mulch will delay frost from entering the soil, buying a few more weeks of rooting time before soil freezes solid.

Leave the mulch intact over winter, and remove in spring as weather consistently moderates, being sure to loosen or remove the mulch before the tulips attempt to grow through the material.

More gardening columns from Don Kinzler

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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