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Do you have some advice on how to control mallow weeds? This has been an ongoing problem that even the powerful herbicides can only contain for just a few weeks. They always come back and completely overrun my garden. Any advice?

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As you have discovered, a mature mallow weed is quite tolerant of most yard-and-garden herbicides, including Roundup and 2,4-D. The herbicides often cause mallow to go yellow, and some of the plants may die; but many eventually recover to become even tougher than they were before they were sprayed.

You probably also have found that pulling, hoeing or rototilling large mallow plants is difficult and only partially effective. Then, there is also the problem of mallow seeds in the soil. Mallow is a prolific seed producer, and its seeds can lay dormant in the soil for years before germinating. In a typical garden there are thousands and thousands of mallow seeds already in the soil just waiting for the right time and conditions to germinate. Whenever those conditions occur, a few new mallow seedlings will emerge; but the majority of the seeds remain dormant awaiting a future opportunity.

Each time it rains or whenever the garden is irrigated, a few more mallow seeds will germinate. So, even if you were successful in killing all of the emerged mallow plants with a single herbicide application, a new flush of seedlings would still appear after each watering or rainfall event for the next several years.

The best advice I can give is to be persistent, and to kill or remove mallow plants when they are small. The strategy is to deplete the soil of its mallow seed supply by eliminating all emerging mallow plants before they have a chance to make more seeds and replenish the supply in the soil. Pulling, hoeing or rototilling can be very effective against small mallow plants. Mallow is also much more sensitive to herbicides when in the seedling and early vegetative stages (before plants get more than two or three inches wide).

Whichever control method you choose, do it early in the development of the weeds. That's when they are easiest to control, and it's the only way to deplete the soil seed supply. It will probably take several years of weeding every couple of weeks before you see the results of reducing the number of dormant mallow seeds in the soil. But in the long run, I believe that's the only way to make real progress.

Posted on 26 Apr 2001

Steve Dewey
Extension Weed Specialist

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