How to help your yard when the weather can’t make up its mind

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Mike will appear at the Calvert County Home Show at the Fairgrounds in Prince Frederick on Saturday, April 28. Find more details here.

When to use corn gluten in inconsistent weather

Dave in Rockville writes: “My forsythia is blooming, but the soil temperature is nowhere near 55 degrees. When should I put down corn gluten?”

Dave is referring to the finding that applying 20 pounds of corn gluten meal per 1,000 square feet of turf at the exact right time in the spring can both feed the lawn and inhibit the germination of dormant weed seeds like crab grass.

Sad Fact #1: Legal limits apply to natural lawn products

Alas, the recently implemented lawn care laws in both Maryland and Virginia make no distinction between a slow-release natural fertilizer like corn gluten and the cheap, fast-release chemical salts that are actually the cause of the environmental damage the laws are meant to deter.

Although exemptions should be considered for ultra-slow-release, non-salt-based nitrogen-rich fertilizers like “CGM,” there currently are no such common-sense exemptions.

The Bottom Line: Whether it’s right or wrong, applying that much corn gluten in one feeding is technically illegal.

Sad Fact #2: You can’t rely on forsythia no more

Dave in Rockville notes that his “forsythia are blooming, but the soil temperature is nowhere near 55 degrees!” Dave is referring to the timing of products like corn gluten meal that are designed to prevent dormant weed seeds from sprouting.

In the past, we have often tied this timing to the blooming of local forsythia, which typically occurs when the soil temperature (as measured 4 inches deep) hovers around the magic number of 55 degrees Fahrenheit.

But most people’s giant yellow shrubs were blooming in full force long before the most recent snowstorm — and my forsythia bloomed in November! So that once fabled formula is clearly now fakakta.

That leaves the actual soil temperature as our guide. Dave is correct that it is not anywhere near 55 degrees now — but the D.C.-area soil probe we use as our guide did reach the magic number of 55 degrees for several days last month. It has since dropped back into the 40s, and no one knows for sure if weed seeds broke dormancy during that warm spell, or if it wasn’t quite long enough for them to “wake up.”

My Magic 8-Ball says “punt.”

Luckily, ‘CGM’ is still the perfect lawn food

Dave in Rockville wants to time the application of corn gluten meal so that it has a chance to prevent the germination of at least some of his dormant crab grass seeds. Normally, that would mean applying the all-natural pre-emergent when forsythia are blooming and/or the soil temperature reaches 55 degrees.

Unfortunately, area forsythia have decided to bloom whenever the heck they feel like it. And soil temps this season have surpassed basic roller coaster swings so much that we are now riding The Wild Mouse. (Watch that sharp corner! Lean in!)

My advice is to wait until the snow melts and the soil is visible again, and spread your corn gluten. It may or may not prevent weed seed germination (that herbicidal property lasts for six weeks after application), but it will absolutely give your lawn a perfect feeding of natural slow-release nitrogen — the food that fuels healthy lawns.

Defeat Japanese beetles by beating their grubs

Amy in Springfield writes: “Thanks for the advice last spring to use beneficial nematodes around my roses to control a ‘holey’ problem in their leaves. I am getting ready to order more nematodes for this year’s application.”

Amy is talking about using beneficial nematodes to control Japanese beetle grubs in the soil before those grubs can emerge as armored adult rose ravagers. Great choice, Amy, as beneficial nematodes are currently the only natural way to kill beetle grubs in the spring.

Be sure to wait until the soil temp is warm enough (follow package directions), and then simply water the millions of microscopic nematodes into your lawn. These amazing little beneficials will seek out and destroy the grubs, which attack both lawn roots (as grubs) and roses (as The Beetles).

Oh, and nematodes don’t harm earthworms or anything else — just nasty grubs.

Killing beetle grubs spring and fall

Amy in Springfield is getting ready to use beneficial nematodes to protect her roses from Japanese beetles. Excellent choice, Amy!

Japanese beetles are very difficult to control in their adult form, but their soft-bodied grub stage is vulnerable to attack by beneficial nematodes — microscopic creatures you purchase by the millions (online and at hipper garden centers) and water into your lawn, where they will seek out and destroy nasty grubs.

As long as the soil is warm and wet enough, the nematodes will be on the attack.

If Japanese (or other “scarab”) beetles are still a problem this summer, be ready to apply more nematodes — or “milky spore disease” powder to your lawn in late July.

“Milky spore disease” — a natural organism originally isolated from Japanese soils — controls grub problems by infecting the individual grubs with a fatal disease that is precisely specific to grubs. The dead grubs then breed more of the disease, giving one application the potential to protect your lawn for years to come.

Important note: Beneficial nematodes work in warm soils of spring and fall, but “milky spore disease” powder only works in the late summer and early fall. (Yes, stores stock it and sell it now, but it won’t work now.)


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