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LifestyleColumnistsJessica Damiano

Garden Detective: Hibiscus, sheet mulch and grubs

Hibiscus moscheutos 'Disco Belle Pink' is one of

Hibiscus moscheutos 'Disco Belle Pink' is one of several winter-hardy, perennial hibiscus hybrids that have been sold on shopping channels over the past few years. Credit: MOBOT Plant Finder

DEAR JESSICA: About 10 years ago, we purchased a hybrid hibiscus from a shopping channel that did not require that it be brought in during winter months. We left it planted in our yard year-round, and it had beautiful flowers every spring and summer. We moved but didn’t take them with us and are now wondering where to find them. — Bob Mudzinski, Port Jefferson

DEAR BOB: Hibiscus is a botanical name, but also a common name typically used for the tropical Hibiscus rosa-sinensis, one of hundreds of species in the mallow family, including rose of Sharon (a hardy perennial) and Chinese hibiscus (the tropical plant either brought indoors for winter or treated as an annual in our climate). Most of these plants are widely available at local nurseries.

Hybridized perennial hibiscus are those bred to withstand colder temperatures. They require full sun and plenty of water, and return year after year, leafing out in late spring or very early summer and blooming from midsummer through autumn, sometimes even until frost. Cut them down to about 6 inches tall when frost turns their foliage black, then apply a couple inches of mulch over their root area for added protection.

Many hibiscus varieties are wildflowers that thrive in swamps and marshes, so they appreciate soggy soil. They were instrumental in developing the hardy hybrids that can overwinter in the Northeast. And they tend to resist deer browsing.

There are others, but the hardy Lord Baltimore, Kopper King, Disco Belle Pink, Bordeaux, Chablis, Grenache, TieDye, Plum Fantasy and Sultry Kiss hybrids have been sold on shopping channels over the past few years, so you might have had one of those.

Check with your local nursery; if they don’t stock them, they may be able to order some for you. If that’s not an option, you can order from an online nursery, but likely will receive much smaller or even bare-root plants.

DEAR JESSICA: Do you have any particular suggestions for getting rid of moles? — Warren Tackenberg, Hauppauge

DEAR WARREN: Moles do not eat plants or their roots. Instead, they feast on worms, insects and mostly grubs that live in the soil. Moles can cause damage as they forage through soil for grubs, leaving unsightly little mounds of soil behind, but they needn't be the target of your ire. It’s the grubs you need to get rid of. The moles will move on when their food supply disappears.

Mole damage is sometimes confused with vole damage, so the first step is confirming whether you have moles. Voles chew up the bottoms of trees and shrubs, and eat plant roots. Instead of soil mounds, they leave behind golf ball-size holes, long, narrow tunnels, and plants that seemingly die overnight.

If you are certain you have moles, the next step would be to confirm that you, in fact, have a grub infestation. Do this by digging up a section of lawn (or garden-bed soil, if that's where you see evidence) that is 12 inches square and a few inches deep. If you have grubs, they will be attached to the sodlike square you remove, or be visible on the soil beneath it. Grubs are whitish, brown-headed beetle larvae that look like shrimp curled into the shape of the letter C.

Now this is important: Fewer than 10 grubs per square foot is considered acceptable. You should only take action if there are 10 or more grubs on or under the 12-inch section of dislocated soil.

Grubs are most vulnerable when they are young, so control measures should be planned for mid-August through mid-September. 

Milky spore powder is a natural product said to target grubs, but it only works against the Japanese beetle grub, and you don’t know which kind of larvae you have. Most readers do not report success with this control method.

A better option is beneficial nematodes, the microscopic, nonsegmented worms that attack soil-dwelling insects like grubs. They already exist in the soil; you'd just be adding more. They will infect the grubs with a bacterium that can kill them in as little as 48 hours. There are many species of nematodes available; seek the Heterorhabditis bacteriophora (Hb) strain, which specifically targets Japanese beetle as well as other grubs.

I do not recommend chemical options because they can be toxic to earthworms, honeybees and other pollinators, pets and wildlife — and some are toxic to humans.

DEAR JESSICA: My husband and I are starting a raised vegetable bed for the first time this spring. We already have it filled with organic soil and are hoping that our compost will be ready. Where can we buy the sheet mulch that you mention in your March 24 suggestion? Or can you explain how we can make our own sheet mulch? — Jeanmarie Rall, via email

DEAR JEANMARIE: I apologize for the confusion.

When I recommend “sheet mulch” to warm the soil for early transplanting of vegetables, I mean the season-extending black or red plastic mulch sheets, commonly sold in rolls at most nurseries to be laid over beds to attract sunlight and trap heat. It also serves as a weed barrier.

The practice of “sheet mulching,” however, is a technique used to smother the lawn or weeds, usually for the purpose of creating new garden beds. That requires applying thick layers of cardboard or newspaper topped with a few inches of soil. The paper, which eventually disintegrate, smothers grass or weeds beneath it. The area typically can be planted within a couple weeks.

Neither method should be confused with "lasagna gardening," also known as "sheet composting." This method involves layering organic matter (like kitchen scraps, yard waste and shredded leaves) into beds so it can decompose into compost and naturally enrich the soil. To complicate matters further, cardboard or newspapers are often put under the first layer. The “lasagna” is watered to hasten decay, and the resulting compost makes the soil easier to work, improves drainage and adds nutrients.

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