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Is your lawn growing onions? How to get rid of pesky weeds

WTOP's Garden Editor Mike McGrath gives advice on pesky onion grass growing in your yard. (Courtesy)

Meet Mike in Maryland

Mike will appear at 11 a.m., 1 p.m. and 3 p.m. on Saturday, April 28 at the Calvert County Home Show at the Fairgrounds in Prince Frederick. Find more details here.

Is onion grass a sign of alkalinity?

Mark in Fauquier County writes: “I have a large lawn that grows an abundance of onions. The lawn covers about an acre and a half so it’s not feasible to try and manually pull all the onions out. Research I’ve done says the presence of onions indicates the soil is too alkaline and I should add lime to the lawn. Do you agree?”

No, Mark, you or your source got it backward. Lime is used on acidic soil to increase alkalinity, not lower it.

But you can add lime — or preferably wood ash — to your lawn if a soil test reveals that the pH is lower than 6.5. Excessive rain can make soil more acidic in our region, and grass will always grow best in soil that’s just slightly acidic to neutral (a pH of 6.5 to 7). Adjusting an off pH will lead to healthier turf that’s better equipped to resist the invasion of weeds like onion grass.

Onion grass directions: Water, pull, repeat

Mark in Fauquier County feels that his acre and a half lawn is too big to try and manually pull out all of his onion grass. That’s probably true — but how much do you use or see the outskirts of this lawn? Removing the clumps nearest your home would probably supply you with the emotional turf relief you seek.

Now, onion grass is a tough weed once it gets established. Herbicides have little effect on it because the above ground growth that gets hit with any spray is tall and skinny, while most of the plant’s energy is underground, stored in and protected by a big onion bulb.

The plants grow new bulbs adjacent to the existing ones every year, resulting in large clumps that are easy to spot and pull in the Spring. Just soak the clump heavily with water, pull slowly at the base and all the bulbs in the clump should pop right out. If the roots don’t come out, you didn’t soak the area well enough and/or placed your hands too high.

Once a clump is removed, it will not grow back.

Again, start by clearing the areas near your home that are the most visible and heavily used. If you have to go searching for a weed, it’s not a real problem.

Better than Green Lantern’s power ring!

A very effective “secret weapon” will make the work of eradicating onion grass go faster.

“The Water Powered Weeder” from Lee Valley Tools is a long spikelike device you attach to your garden hose that allows you to deliver a super-concentrated burst of water to the root zone of offending plants with the pull of a trigger while you remain standing. It’s a comfortable 43 inches long when fully assembled.

Sometimes the laserlike blast of water loosens the roots enough for you to pull the plants out easily; and sometimes it pops them right out of the ground for you!

Note: The Water Weeder was originally designed with dandelions in mind and is just as effective at assisting with their removal.

Speaking of dandelions ….

In his original email, Mark in Fauquier County recounted that he also has lot of dandelions.

Well, those pretty yellow flowers are a sure sign of compacted soil. Assuming that Mark has a cool-season lawn (composed of bluegrass, rye, and/or fescue), he should plan to have his turf core-aerated this coming fall.

Pulling little plugs out of the soil to reduce the overall underground density can do wonders for the health of a lawn, but it must be done at the correct time of year: In the fall for cool-season lawns, spring for warm-season lawns of Bermuda or zoysia.

Relieving soil compaction allows the roots of your grass to grow deeper and stronger and naturally crowd out weeds.

Note: The soil should be bone dry for this procedure and then watered well afterward. Do not attempt to aerate a wet lawn.

Cut sharp, look sharp

The long-term answer to lawn weeds does not lie in herbicides or even in really cool gadgets like the Water Weeder, but with proper lawn care.

The photo Mark sent of his lawn actually looked pretty good, but it’s clear that the grass is being cut too short, and that’s an invitation for weeds to move in.

Get a new blade for your mower or get the old blade sharpened and raise the cutting height so that the grass is three inches high after cutting. And always return your clippings to the turf; they’re 10 percent Nitrogen — the perfect lawn food.

If you cut it at the right height with a sharp blade and don’t steal its food, your lawn will grow the kind of deep, strong roots that crowd out weeds naturally.

Note: In the photo the lawn looked good except for the tire tracks visible at the upper left. You should never drive on your lawn and never never never drive on it when the soil is wet — you can cause permanent damage.


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