invasive clover?

Asked June 23, 2020, 9:29 AM EDT

it looks like clover. last summer it took over our yard in the mulched areas. Sprayed it with round up and it cleared it up last year but this year its coming back full force. Don't want to use round up. Suggestions?

Montgomery County Maryland

1 Response

This is not clover, but it does look like you might have two different weed species between your photos (the second photo isn't clear enough). Glyphosate (Roundup) is a systemic chemical, but only absorbed by what foliage it touches. These are seedlings rather that sucker sprouts of last year's weeds, hence why that herbicide application has had no effect on them.

These plants are a bit young to have enough distinguishing features for ID. They resemble Pokeweed (Phytolacca americana) as well as an Amaranth-family weed like Redroot Pigweed (Amaranthus retroflexus). The former is native and a perennial; the latter is non-native and an annual.

The simplest solution is to kill them with disturbance (hoeing) or smothering to block light and moisture until their reserves are exhausted and they die. You could also use a weed-burner tool, though certainly use caution to avoid setting mulch on fire or damaging any nearby desirable plants. Disturbance could potentially bring up a new batch of weed seeds to the surface, so adding fresh mulch afterwards (to a depth of up to 3") will help discourage germination. There are pre-emergent herbicides safe for use around (most) established perennials, shrubs, and trees, but you would have to see what product options you have and what weeds they are labeled for.

Their successful germination in this current mulch layer may mean that it is in need of refreshing to increase its depth a bit. (Keep mulch off of desirable plant bases, however.) It also may indicate a consistent supply of moisture is available, which tends not to happen in surface soil unless it is regularly irrigated. (Rains have been patchy in the area so far this summer, so perhaps you've had enough rainfall.) If you are irrigating, be sure to only do so when the soil has dried enough several inches below the surface. Getting new lawn or wildflower seed bed established is the only scenario when frequent, light waterings are beneficial.

Miri