Gardener’s Corner

March 2023

Monthly Article by Cate White, San Joaquin County Master Gardener

Weeds versus Volunteers

A weed can be defined as any plant that grows where it is not wanted. Most plants that we think of as weeds grow prolifically, spread easily and are often hard to remove. There are many strategies for removing them, but it is best to use harsh chemical herbicides only as a last resort. This time of year, weeds are growing fast, especially since we had such abundant rainfall in the last few months, and now is the time to deal with them. To reduce the number of weeds in your yard over time, it’s important to remove them before they bloom and set seed.

What are the best strategies for keeping weeds under control? According to the University of California Agriculture and Natural Resources program, the best practice is to employ IPM, or Integrated Pest Management. This simply means using a variety of methods in a thoughtful, strategic way, starting with the ones that cause the least environmental harm.

One of the first lines of defense against weeds in planting beds is to use mulch. Bark, in chips up to 1½“ in size, is the preferred mulching material. Larger chips let in too much light to keep down weed growth. Rocks are poor mulching material since they can be too reflective (white rocks) or heat absorbing (dark colored rocks), causing damage to plants and their roots. Rocks are also difficult to weed around. When first laying down mulch, it may be helpful to put down an additional weed barrier, such as landscape cloth, or a pre-emergent herbicide. Black plastic is not recommended since it doesn’t allow the soil to breathe. Using landscape fabric is best in woody perennial beds that won’t be disturbed for about 4 years. Once you have installed the fabric and covered it with a layer of mulch about 1” deep, remove any weeds that appear when they are small by hand or with spot application of herbicidal spray. If you do not use landscape fabric as a weed barrier, add up to 4 inches of mulch, being careful to leave open space around the trunks of woody plants. An additional advantage of mulch is that it helps to conserve moisture in the soil. Herbicides can be used on stubborn perennial weeds.

In vegetable and annual beds, pulling weeds by hand and cultivating with hand tools are the best choices. Herbicides are definitely not recommended in vegetable beds. When planting annuals or short-lived perennials, try to plant close enough together to keep the ground shaded, discouraging weed growth.

Consistent mowing will keep down most broad-leaved weeds in lawns. For low-growing weeds, hand removal is best. Use herbicides as a last resort, after identifying your lawn turf-grass species and the specific weeds that are a problem, so you know the appropriate chemicals to use.

Occasionally, you will find a plant that has volunteered in your garden that is not generally thought of as a weed, but a cultivated plant. I often find small oaks sprouting in my yard where I do not want them; they are usually planted by jays. Since they have long taproots, they can be hard to pull out. Other plants I’ve found growing along with the weeds include lantana and nandina. If you dig these volunteers out when very young, you can easily transplant them to an appropriate place, and you’ve gotten a “bonus plant”. I also plant several plants that I know will reseed year after year, crowding out weeds in the process. These include violas like Johnny Jump-ups, flat-leaved parsley, calendulas, and feverfew, and nasturtiums. This is an effortless way to create attractive patches of flowers or herbs in your yard that return year after year.

A few weeds common to our area are pictured below. Weeds will always be a fact of life for gardeners, but using some basic cultural strategies can help to minimize them.

March Garden Checklist

Early March is still time to plant lettuce, parsley and chard seedlings. Flowering Spring annuals, such as pansies, sweet peas and ranunculus can also be planted now. Peas, carrots, beets and radishes can be planted from seed.

Plant summer bulbs such as gladiolas and dahlias.

Most plants, including lawns, will appreciate an application of an all-purpose fertilizer now.

Continue to control ants, slugs and snails using baits. Iron based snail and slug bates are the most environmentally sound and safest for use around pets.