- Author: Christine Lai
"Sea of red... mulch, that is" by WSDOT is licensed under CC BY-NC-ND 2.0.
Benefits of Mulch
Mulch is one of the gardener's most useful tools: applied correctly, it suppresses weeds, improves water retention in soil, and keeps the soil temperature down. But does the kind of mulch matter? And do you tie up nitrogen when you use high carbon materials like wood chips as mulch?
Color matters
First of all, UC researcher Janet Hartin writes, don't use black dyed wood chips as mulch. Hartin, a resident of Coachella Valley, found that black dyed mulch, along with synthetic lawn and asphalt, can superheat surfaces up to 65 degrees hotter than the surfaces of plants in a study she conducted in the valley over the months May through August.
To till in or not?
Second, what about the carbon to nitrogen ratio of your mulch? This becomes an issue when mulch is tilled into the soil. Tilling in high carbon to nitrogen ratio materials like wood chips will tie up nitrogen in the soil leading to stunted plant growth. As the population and activity of the decomposers in the soil increase, they consume carbon and nitrogen, competing directly with garden plants for limited supplies of nitrogen. However, leaving mulch on top to slowly decay over time will not have this effect.
If you are tilling in your mulch, UC Riverside researchers (Pittenger 584) found that mixing in high nitrogen materials like grass clippings in with high carbon wood chips offset any temporary nitrogen tie up.
Tilling in green manures like alfalfa straw will supply nitrogen and has been found to be especially valuable to citrus trees.
Mulch and pests
Other things to consider when mulching are pests. UC Riverside researchers found that voles and gophers preferred trees with mulch. Pill bugs may find a home in leaf litter. Monitor plants and be sure to keep mulch away from stems.
A few notes on proper application
When applying mulch to trees, be sure to keep the mulch from touching the tree trunk and keep from piling too much on top of the root ball. Roots can grow up into the mulch and girdle the trunk. For other plants, keep mulch 4 to 6 inches away from stems. Apply 2 to 4 inches deep for maximum benefits.
Work Cited
Pittenger, Dennis R. California Master Gardener Handbook. Edited by Dennis R. Pittenger, University of California Division of Agriculture and Natural Resources, 2015.
- Author: Martin Saiz
- Author: Anna Judy de Torres
What is California's native milkweed and why should we plant it?
Native milkweeds are perennials with clusters of small (usually white or pink) flowers that grow in every eco-region of California. The native milkweeds are an important nectar source to a range of pollinators including bees, hummingbirds and butterflies. Native milkweeds go dormant during the winter and sprout anew during the spring.
Milkweed is especially well known for its importance to monarch butterflies, since they are the required host plant formonarch caterpillars. No milkweed means no monarchs. Land development and use of herbicides have dramatically reduced the presence of native milkweed by taking away the flatlands and meadow areas where the plant grows well. The monarch butterfly population has dramatically declined and the best way that gardeners can support the monarchs is by planting their necessary host plant - the milkweed - as well as other needed nectar plants and by avoiding the use of pesticides.
The Xerces Society lists 15 different native milkweeds to California but recommends that Narrowleaf Milkweed (Asclepias fascicularis) and Showy Milkweed (Asclepias speciosa) as the best species to plant due to their ability to grow in the widest range of conditions and the opportunity to buy them commercially.
Is native milkweed hard to grow?
Antonio Sanchez of the Rancho Sierra Vista native plant nursery says, “Of all the native milkweed species, Narrowleaf Milkweed is the easiest to grow. It is true that it is a little more difficult to grow than the very easy and showy tropical milkweed, but not by much. It is like the difference between growing spinach and watermelon, you just have to know where and when to plant it. If growing from seed, always start the seed in the warm months, from April to July. If
growing from live plants, always install from March-August. Water deeply and frequently the first year, once or twice a week. After the first year, plants normally thrive on twice a month waterings. Plants thrive in full sun, but tolerate part shade as well, and can be successfully grown in sandy or clay soils.”
Where can I buy it?
Unfortunately, buying native milkweeds is not as easy as a visit to your local outside box store. Many only sell tropical milkweed. You could certainly request it though! Ventura County has even taken the unprecedented step of banning the sale of tropical milkweed.
Most native plant nurseries and many independent nurseries will have narrowleaf milkweed for sale during its prime growing season, from March to August. You can search on the California Native Plant Society website Calscape.org to find nurseries in your area that carry one of the native milkweed species.
If I have tropical milkweed planted, what do you recommend?
Most experts agree that if you have tropical milkweed planted, you should cut it down to the ground as winter approaches in order to mimic the growth patterns of native milkweeds and allow a healthier regeneration of the plant in the Spring.
The controversy over tropical vs. native milkweed stays strong in some gardening circles but native plant nursery manager Antonio Sanchez recommends the following, “If you have tropical milkweed in your garden, keep it going as you get your native milkweed patch established. The first year, cut back your tropical milkweed to the ground around Thanksgiving, and to the ground again around Valentine's Day. After one or 2 years, your native milkweed patch should become established, and you can then completely remove your tropical milkweed plants.”
What are the Los Angeles Master Gardeners doing to support the monarchs?
Los Angeles UC Master Gardener Martin Saiz collaborated with the native plant nursery at Rancho Sierra Vista to successfully request a major grant from the National Fish and Wildlife Fund (NFWF). The purpose of the grant is to address population declines and ensure the survival of the monarch butterfly. Over the next two years, the grant will fund gathering native milkweed seed from across the Santa Monica Mountains, propagating thousands of milkweed plants at the nursery, planting milkweed in 150 nearby acres, and establishing a network of milkweed way stations in 300 community, school, senior, and shelter gardens across Los Angeles County.
