Mulch from cypress trees (Cupressus spp.) is an attractive, moisture-conserving cover for your flowerbeds and other areas of the garden. Although cypress is generally a benign, nontoxic substance, mulches can sometimes be dangerous in other ways. Vet them carefully, especially when using in a vegetable garden.
Cypress trees' U.S. Department of Agriculture plant hardiness zone ranges depend on species, but they are generally adapted to warm climates. Italian cypress (Cupressus sempervirens) and Arizona cypress (Cupressus arizonica), for instance, do well in USDA zones 7 through 9, while Kashmir cypress (Cupressus cashmeriana) does best in USDA zones 9 and 10. They are evergreen conifers that appreciate full sun well-drained soil. Their reddish bark and wood makes for good-looking mulch.
The wood from cypress trees is generally not harmful to small animals. Because cypress heartwood can be repellent or even harmful to termites that consume it, a small possibility exists that it may be harmful to other, more beneficial insects. However, no problems have been reported from the use of cypress mulch. No reports exist of it killing small mammals, such as rabbits or squirrels.
Large Animals and Humans
Cypress is non-toxic to larger animals as well, including humans, but you should be aware of a few exceptions. Fireweed (Bassia scoparia f. trichophylla or Kochia scoparia), also known as summer cypress, is an annual shrub that may prove toxic to horses. While it is not a true cypress and does not possess the woody parts required to make mulch, you should not assume it is nontoxic simply because it is sometimes labeled a cypress.
Even though mulch is a beneficial, usually safe addition to the garden, it can turn bad in some instances. Usually this is more dangerous to the plants than to you, such as when mulch sours, producing a build-up of acidic acid, which can burn plants, causing them to wilt and die. If your mulch smells like vinegar, ammonia, alcohol or sulfur, do not use it on the garden. Always make sure before you spread mulch made from fresh wood on a vegetable garden, rather than recycled and dyed wood products. These can sometimes contain harmful additives, which might be bad for people and animals. Mulch can also harbor molds or fungus, which may damage plants.
Putting down mulch is one of the best ways to conserve moisture in the garden. It also discourages the growth of weeds, reducing the amount of work you need to do to keep it attractive and weed-free. Because cypress mulch holds so much water, you should wet it thoroughly before placing it on the garden. Otherwise you run the risk of placing a thick water barrier between the soil and the water you will administer as dry mulch will simply soak the water up.