Hello Frances,

To control weeds that are sprouting from seed consider using a granular preemergence herbicide that has the active ingredient trifluralin in the early spring. Preen is one brand and there are other brands that contain trifluralin, too. Read the label for the “active  ingredients”, usually found  in small print on the front or back label.

Applying the preemergence herbicide on top of the mulch as directed on the label will help prevent new seed germination.

If you start seeing winter annual weeds a second application time around early-mid August may be recommended. Examples of winter annual weeds can be seen in this article: https://www.canr.msu.edu/news/spring-blooming-lawn-and-garden-weeds

Trifluralin will not control existing weeds or perennials that continue to grow from their roots.

If you can, update this question with a couple clear pictures of the weed you have. We may be able to identify it and give you the correct control options for it. Try pulling a couple with their roots and lay them out to take a picture so we can see the leaves, roots , and any seed pods or flowers.

To attach pictures:

Follow the link in your email into your Ask Ext. Question.

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Pictures in standard format of jpeg work. Each photo must be 8 megabytes or less in size.

As always please, read nd follow all directions on the label of any product you use. 

Attached are photos of two of the most prevalent weeds, with a close up of the one that looks like a clover leaf. This one has strong roots. 

Also, snap dragons have started to take over. They seed themselves or something.  

Thank You for your assistance.  

Best, Fran

The first picture is common chickweed, Stellaria spp. It sprouts from seed every year both in spring nd in fall.

The second two pictures are wood sorrel,  Oxalis stricta.

Using chemicals on weeds must be done with caution since the same weed killers that destroy the dicot weeds can harm trees , shrubs, and perennial garden plants, most of which are also dicots.

weed control in landscape- https://yardandgarden.extension.iastate.edu/how-to/weed-control-perennial-gardens-and-landscapes

Your best bet  is to hand weed out as much as you can each year before they set seed and put down a pre-emergent herbicide which controls seeds and seedlings. Pre-emergents will not harm healthy perennial plants already established when used according to the label. You may have some success using an organic pre-emergent such as corn gluten meal, but results have been mixed using this product.

By controlling the sprouted weeds before they set seed each year, you will eventually have fewer and fewer seeds sprouting in the bed.
Using a deep mulch in the bed 3 to 4 inches thick also helps control weed seeds. Many seeds need light in order to germinate and a deep mulch prevents sunlight from reaching them. Keep any mulches pulled three or 4 inches back from your perennial shrub and tree trunks.

Here are bulletins on both of the weeds in your pictures for more details.
https://extension.psu.edu/lawn-and-turfgrass-weeds-common-chickweed
https://www.k-state.edu/news/turf/articles/2018/09/yellow-woodsorrel-oxalis-stricta-control.html