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The Journal Gazette

Saturday, June 09, 2018 1:00 am

Weeds may give hints on soil type

Ricky Kemery

Question: I have heard that the weeds growing in a particular area can indicate what type of soils one might have. Is this true?

Answer: A weed is defined as a plant that does really well in a place where it isn't wanted. So one person's weed sometimes can be another person's wildflower. When I was researching how to establish prairie wildflowers as a part of my master's degree research project at Purdue University, I was intrigued to find several prairie wildflower species included in the weed plots at the Purdue Agronomy farm.

It is true that certain weeds prefer specific sites. I always look for moss growing near foundations when I perform site visits. The moss tells me the area is often poorly drained, even if it looks dry on the surface. Nikki Phipps, author of “The Bulb-o-licious Garden,” lists weeds that prefer specific areas in her article in Gardening Know How. Many weeds can occupy all areas, but if a particular weed occupies a specific area of your landscape, it can give an indication of soil type or drainage.

There are other common weeds that prefer wet soils.

Spotted spurge, a prostrate weed with milky sap, also prefers lawns that are mowed too short. Ground Ivy (Creeping Charlie) will often occupy moist shady areas in the landscape. I rarely see this mint family weed in dry areas in full sun. Ground Ivy is particularly nasty in the sense that it spreads by seed and underground rhizomes.

Purple and Yellow Nutsedge can be difficult because they have a storage bulb (a nutlet) that remains even when one tries to pull the weed. Violets also occupy moist shady areas. I sometimes wonder why people want to get rid of them because I think they are very pretty. I used to collect them and give them to my Mom on Mother's Day.

Many common weeds prefer the heavy compacted clay soils common in our area. Plantain prefers close-mowed lawns, so just raising the mower blades and core aerating can greatly reduce plantain populations. Quackgrass, a perennial grass with long fleshy rhizomes, prefers bare areas and is one of the most difficult grassy weeds to control.

Garlic mustard is a biennial weed that flourishes in partially shaded areas on the edge of the forest. This weed must be pulled and destroyed before it goes to seed. Otherwise it will take over these woodland edge areas.

The most difficult weed to control is Canadian Thistle. This perennial weed that spreads by underground rhizomes and seed often is found in fence rows or bare soil or thin turf – anywhere it can gain a foothold. This weed is found most often in sunny to part-sun areas. Efforts to control Canada Thistle by pulling or tilling, most herbicides, or shading are largely ineffective.

In my experience, only herbicides that contain the active ingredient clopyralid have any effect on this monster of a weed.

The Plant Medic, written by Ricky Kemery, appears every other Saturday. Kemery retired as the extension educator for horticulture at the Allen County branch of the Purdue Extension Service.