Garden Plot: How to deal with moles and grubs in your backyard

Editor’s note: Mike McGrath is on vacation; this week’s Garden Plot was first published on Sept. 7, 2018.

Miserable moles

Valerie in Howard County writes: “Any advice about moles? We have them in the backyard. And my next-door neighbor is also hosting them. I’ve signed on with a professional exterminator who has begun trapping them. The neighbor is still getting estimates and advice on how to proceed. Do we need to talk to our other adjacent neighbors? We’ve lived in our home for 25 years and never had this issue.”

In my experience, moles often arrive unannounced, Val. Unlike voles (which are sighted and have a shew-like appearance), moles are blind, look really weird, live their life underground and don’t eat plants.

They do, however, make an ungodly mess of lawns with their close to the surface tunnels. Unfortunately, traps are often the response that at least temporarily solves the problem.

Get rid of your grubs

Does Valerie in Howard County have other options?

Yes. Moles are the underground equivalent of teenage boys; they live in the dark and eat no vegetables. Moles thrive on a diet of earthworms, grubs and cicada larvae.

You can’t — or shouldn’t — get rid of your earthworms, but you can eliminate the grubs with milky spore, beneficial nematodes and/or “BTG” the newest strain of Bt. All are “specific”, meaning they pose no harm to you, your pets, bees, butterflies, toads — the whole nine yards.

And this is the time of year to try one or more of them, as the grubs are close to the soil surface, feeding on the roots of your lawn and in their least protected position.


  • “Milky Spore” is widely available in powdered form. Its technically a “disease” but one that only affects the grubs of Japanese beetles. If there are enough grubs in your lawn when you use it, it should stay effective for many years. Only works when applied in late summer.
  • Beneficial nematodes are microscopic predators; millions of them are packaged into sponges that are no bigger than a pack of gum. You drop the sponge into a watering can and then water the nematodes into your lawn where they attack and kill grubs of all species. Widely available via mail order and some hipper garden centers, nematodes are also effective after the soil warms up in the spring.
  • BTG is the newest form of “Bt”, a family of naturally-occurring soil organisms, some of which have pest-controlling powers. This Bt comes in two forms: a spray that kills adult beetles that munch on sprayed plants and a powder that kills grubs feeding in the soil. The mail-order firm Gardens Alive sells the latter version as “Grubhalt“; and it may be available at some retail locations. (It only came on the market this year.)

Note: Getting rid of grubs greatly reduces a mole’s food supply (and helps your lawn and roses) but it’s no guarantee that the moles will then move on. Sometimes they do, sometimes they don’t.

Stink ‘em out!

Does Valerie in Howard County have other mole control options? Yes — castor oil preparations.

Sold under wonderful names like “Mole-a-tov-cocktail”, concentrated castor oil smells real bad. Apply it to the mole-affected lawn in liquid or granular form and it will impart its distinctive scent underground, where it will annoy the heck out of subterranean troublemakers like moles, voles, gophers and groundhogs.

Find the product with the highest concentration of active ingredient, apply it heavily now — and especially in the spring — and the moles may choose to move next door. Have the neighbors’ chip in on a pallet and Howard County might become a mole-free zone!

You need thatch to dethatch

Bill in Fairfax Station writes: “Should a lawn be dethatched? I have heard both views — Yes and no.”

We then asked Bill if he had a lot of thatch. He replies: “I do not have a lot of thatch that I can see. The last time I dethatched was about 10 years ago. I always feed and overseed the lawn in the fall. This year I want to core aerate as well as apply lime. The latter hasn’t been done in at least 15 years. Trying to get all this done by late September.”

OK; now you never want to dethatch and core aerate in the same year. Although both have long term benefits, they are stressful to the turf, and since you don’t see thatch, there’s no need to remove what isn’t there. Stick with the core aeration — always a good idea — and stop looking for trouble!

Lawn care for bill

Bill in Fairfax Station wants to dethatch, feed and overseed his lawn, core aerate and apply lime.

This is a sure sign that Bill has too much time on his hands — especially since he can’t see any thatch! (This is what happens when the Nats stop being fun to watch.)

Anyway, Bill should have a core aeration performed to reduce soil compaction, which can work wonders for a tired turf. He mentions that his lawn is fescue, which makes the overseeding an excellent idea, as fescue lawns do best when they get some fresh seed in the fall — which is also the right time for a feeding.

But lime is never a “necessity.” Lime is recommended when the soil becomes acidic, but can cause problems if the soil if fine. Always have a soil test performed and only add lime if the Ph is low.

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 Garden Editor for WTOP since 1999. Send him your garden or pest control questions at

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