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Garden Guru: What weeds are telling you

Photo by JOHN PORTER
Spiky, light-green nutsedge is a weed, and it sticks up through many lawns, including the Garden Guru’s.

By John Porter

CHARLESTON, W.Va. — Sometimes it seems like there is just this one weed that has to ruin everything.

It grows out of control, ruining the aesthetic of your lawn, landscape or garden. It outcompetes the things you actually want to grow. It looks horrible and grows way too fast to keep under control.

I know that some people don’t mind weeds, or even appreciate them (many are tasty — perhaps that’s a topic for a different day), but for many gardeners, weeds can be a full-time control job.

While weeds do happen to the best of gardeners, there could be some very specific reasons why you can’t control certain weeds. Conditions could exist with the lawn, landscape and garden that make weeds thrive and thus harder to control.

Your weeds could be telling you just what the problem is, if you would just take the time to sit down and pay attention.

What the weeds are saying

Any number of causes can be increasing the likelihood of weeds in your lawn or garden. To get to the root of the issue, let’s examine some common problems and discuss which weeds those problems can lead to. By knowing which problem causes which weeds, it can be possible to reduce or eliminate weeds and reduce the use of herbicides to control them.

Soil compaction happens when the top layer of soil where the majority of roots reside becomes compressed. This is very common in heavy soils such as clay and loam, but can happen to the best of soils under certain circumstances such as heavy traffic, overtilling (yes, tilling causes compaction), working the soil when it is too wet, and amending with too much sand.

We often think of soil as just the mineral and organic components that we see, but it also contains a significant amount of air and water. Compaction results in less air space in the soil and often leads to a reduced oxygen level in the soil. It can also significantly reduce drainage, allowing water to sit in the soil and displace more air.

Roots need oxygen to live, so when oxygen is reduced it makes it difficult for most plants to grow. Some weeds, though, have adapted to growing in low-oxygen environments and thrive when the rest of the plants you want to grow are suffocating.

These are often weeds that you may find in the bottom of roadside ditches, where poor soil and water reduce oxygen levels. Weeds that thrive in compacted soil include thistle, dandelion, crabgrass, Queen Anne’s Lace and nutsedge.

This last one, the sedge, is one that I’m getting more and more complaints about and suffer from myself in the landscape. It looks like grass, but grows much faster, forming bright green spikes through the yard that, if left unmowed, will produce a spiky head.

It is not easy to control. I think its recent explosion has been caused by our development of a “rainy season” over the last few years. Most of last summer and a majority of the early part of this summer had excessive rainfall, which could make soils wet enough long enough to cause the problem.

So how do you correct compacted soils? In the lawn, you will need to use an aerator. This is a little piece of equipment that you can buy, but can also usually rent from hardware places or equipment rental places. It pulls little plugs up out of the soil, allowing the soil to expand and relax.

To help reduce the cost to you, it could be effective to work with some friends and neighbors to rent the aerator for a day and share it. If you see ads for spikes you put on the bottoms of your shoes, or if someone tells you to wear a pair of cleated shoes and walk over the lawn, just ignore them. Those practices actually increase compaction, not fix it.

Soil pH is an issue I’ve recently talked about, but knowing that it could lead to weed problems can encourage you to test and amend your soil even more. Both acidic (low) and alkaline (high) pH levels can contribute to their own specific set of weeds.

Acidic soils can lead to weed issues such as annual bluegrass, dandelions, stinging nettle, purslane, lamb’s quarters, sorrel and clover (though I don’t consider clover a weed that needs to be controlled). Alkaline soils can lead to issues with weeds like chickweed, Queen Anne’s lace and spurge.

Lack of competition for space and nutrients can also lead to weed problems, especially in the lawn.

Here’s where I pull out my old drum of mowing height. Cutting grass too short reduces its vigor and makes room for weeds to poke their heads through. A proper mowing height of 2½ inches or more will help alleviate a lot of lawn weed problems. Leaving the clippings on, instead of removing them, will also increase fertility, organic matter and lawn health. Some weeds, such as crabgrass, will thrive in low fertility when the grasses you want to grow do not.

This week in the garden

n Sow fall carrots.

n Seed spinach.

n Seed lettuce for fall crop.

n Dig late potatoes.

n Seed lettuce for a fall crop.

n Seed fall turnips and radishes.

n Dig late potatoes.

n Order/buy spring bulbs.

n Plant crocus bulbs.

n Aerate lawn.

n Renovate lawn or reseed bare spots.

n Divide peonies.

n Build a cold frame.

John Porter is the WVU Extension Service agent for agriculture and natural resources in Kanawha County. Follow him on Facebook, Twitter at @WVgardenguru and online at wvgardenguru.com. Contact him at john.porter@mail.wvu.edu or 304-720-9573.


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