Common mallow (Malva neglecta) is a broad-leafed, bushy weed. They can grow all year, though I usually see them in the spring and summer. They are deep-rooted and hard to pull once they’ve grown, so it’s best to pull when they’re young. Mallow reproduces by seed, which can lay dormant in the soil till the shell is nicked enough that water can get in – essentially, when the core gets enough moisture to begin growing. “If allowed to mature to the point of producing seed, the amount of seed in the soil will cause increasing problems in future years.” (per UC Davis)
The most widespread of the weedy mallows in California are Malva neglecta (common mallow or cheeseweed), and M. parviflora (little mallow, which is also called cheeseweed). These two varieties look very similar. The easiest way to tell them apart is by the flower and fruit, which looks like a wheel of cheese, hence the name.
Mallow causes problems with farming equipment, houses pests and diseases that are harmful to crops, it can accumulate nitrates in such high quantities that it is poisonous to livestock, and poultry that consume the leaves or seeds can lay low quality eggs.
According to UC Davis, “There are no chemical controls available for home use that are effective for controlling mallows.”
Some mallow plants are grown with a purpose – these include cotton, hibiscus, and okra.
Sunset Western Garden Book
UC Davis Integrated Pest Management website:
An Hour to Garden