Garden Plot: Outdoor ants are good for the soil

Roses want compost, not wood mulch

Laura in Glen Burnie, Maryland writes: “My elderly father’s house has shrubs planted all the way across the front; Japanese yew, azaleas and some Knock Out roses (which he mulched with wood chips that I will be raking away this weekend). Everything is growing ‘fine,’ but the soil is very sandy and has never really been fertilized. Should I try to improve the soil by putting down some Leaf Gro?”

Absolutely, Laura. Rake away that wood mulch — especially around those roses — and give everything — especially those roses — a nice mulch of Leaf Gro.

Made from fall leaves collected in the state of Maryland, Leaf Gro is great compost, and compost protects roses from dread diseases as it feeds them.

Use grass clippings wisely

Vicki in Oakton, Virginia writes: “I am trying to keep the weeds down in our vegetable garden. Our lawn service will not collect the clippings, so I’m looking for other “cover.”

Stop right there Vickster! If your lawn service treats your lawn with herbicides, the clippings are poison to non-grass plants. They are dangerous even when composted. Fully finished compost made with treated grass clippings as an ingredient has been shown to kill garden plants. They must be returned to the turf.

But even with herbicide residues, those clippings are still the perfect food for your lawn. Ten percent nitrogen by weight, clippings returned to the turf provide the perfect light snack in between regular feedings for lawns, and they help break down any thatch that’s built up at the soil surface.

If not clips, what to use as mulch?

We warned Vicki in Oakton not to use grass clippings from a treated lawn as a garden mulch; the persistent herbicides used by most services can kill non-grass plants.

The original herbicide packaging, which lawn care customers never see, warns specifically against using treated clippings as mulch.

The best mulches for a vegetable garden are compost, such as Maryland’s Leaf Gro product; pine straw and/or pine fines, which are available at many local independent garden centers; and shredded leaves saved from last fall. (Once they’re shredded, you can fit 12 to 20 bags of whole leaves into a single bag.)

But we have to stress that nothing will ever really prevent weeds in a flat-earth vegetable garden, especially if it gets tilled every spring.

Flat-earth gardens are always under attack by grasses that spread laterally. And tilling digs up and replants untold numbers of weed seeds that were previously safely interred.

Raised beds filled with clean compost and screened topsoil start out weed free and stay that way! The framed sides prevent grassy intrusion; and raised beds are always no-till because you never step in them and compress their soil.

He is got ants in his plants

Marc in North Potomac writes: “I have a raised bed that’s 4-foot-wide, 8-feet-long and 16 inches high. Everything grew well the first year, but last year (the second year), my peppermint and spearmint took over. I was told they are invasive, so pulled them out by the roots and ants came out like crazy! I was told they are feeding on the roots still below ground. I tried several applications of Garden Safe Diatomaceous Earth, but the ants still abound.

“Was the Diatomaceous Earth harmful to the soil or the plants? And should I till to try and get rid of the ants?

Yes, mints can easily take over a garden bed.

No, ants will not eat the roots of your plants.

Yes, diatomaceous earth (DE), a natural-mined product approved for use in organic agriculture, is safe to use; but its most effective against slugs and other soft-bodied pests.

And finally, outdoor ants are not a problem; in fact they benefit the gardener by aerating the soil and eating weed seeds.

Care and feeding of raised beds

Marc in North Potomac continues with question about raised bed care. He writes:

“Do I need to get rid of all of last year’s plant roots? Like with a tiller?”

Do not till a raised bed, Mark. Just soak the soil thoroughly and slowly pull up the old roots.

“What type of new soil should I top the beds off with? Or should I mix any new soil in?”

No mixing, Marc! New soil, specifically compost, should be added to the top.

“What do I use for fertilizer? Eggshells?”

Eggshells go down in the planting holes of tomatoes to prevent blossom end rot; the fresh compost on top of the beds will feed your plants.

Mike McGrath was editor-in-chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated public radio show “You Bet Your Garden” since 1998 and WTOP Garden Editor since 1999. Send him your garden or pest control questions at

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