Monthly Article by Cate White,
San Joaquin County Master Gardener
Now that spring has arrived with warmer temperatures and longer daylight hours, plants are growing like weeds. Including, of course, the weeds themselves. Now is the time to dispatch them.
To reduce the number of weeds in your yard over time, it’s important to remove them before they bloom and set seed. Once they have released their seeds, you will be dealing with them for years to come. So 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, so it is not recommended for annual or short-lived perennial beds. 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 to discourage rot. An additional advantage of mulch is that it helps to conserve moisture in the soil. Remove weeds as described above.
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, and only after identifying your lawn turf-grass species and the specific weeds that are a problem, so you know the appropriate chemicals to use.
A few weeds common to our area are pictured. Weeds will always be a fact of life for gardeners, but using some basic cultural strategies can help to minimize them.
Information for this column was taken from the University of California Agriculture and Natural Resources division Publications “Weed Management in Landscapes”, #7441, and “Weed Management in Lawns”, #74113. Links to these publications can be found on the UC IPM web site.
April Garden Checklist
- Warning for Cat Owners: Lilies are highly toxic to cats. This includes Easter Lilies, Asiatic Lilies, Star-gazer Lilies, Day Lilies and more. All parts of the plant are toxic, causing kidney failure. Even licking lily pollen that has rubbed onto their fur or drinking water from a vase containing lilies can be fatal for cats. Cat owners should avoid bringing Easter Lilies into their homes. If you think your cat has come into contact with a lily plant, seek immediate veterinary care.
- Start planting frost sensitive plants now, including citrus, tomatoes, eggplants, peppers and basil
- Control aphids by spraying plants with a strong stream of water or applying insecticidal soaps or oils. Monitor citrus for Asian Citrus Psyllid.
- Fertilize citrus, deciduous fruit trees and flowering shrubs with a slow release fertilized if not done in March
- Adjust irrigation according to the weather and be sure plants are properly mulched
- Prune winter flowering shrubs like viburnums and camellias
- Keep up with weeds by pulling or cultivating