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How to Mulch Your Garden

Pros and cons of straw, paper, ­plastic and reflective mulches

It is a big mistake to mulch your tomato plants when you plant them. When organic mulches such as straw are applied at planting time on cool soil, the cool will linger. This will retard growth, flowering and fruiting. Wait to mulch vegetable gardens until soil temperatures are between 70 and 75 degrees.
    Straw, the most common organic mulch, is generally weed-free and relatively inexpensive. Never use hay if you wish to avoid major weed problems in the future. Hay is often harvested after the seed heads are well developed, and some bales of hay may contain other plants.
    Newspapers are another common mulch, but some people fear that inks may contain heavy metals and glossy paper might contain chemicals. Nearly all black inks used are made of soy. I wish printers were still using zinc-based inks because many of our soils are deficient in zinc, an essential plant nutrient. The colored inks are also organic in nature. The gloss on some papers is the result of the paper being treated with special clay that is harmless.
    It takes 12 to 14 sheets of newsprint to provide adequate depth for weed control. To keep it from being lifted by wind, soak the paper with water immediately after laying it on the ground. Laying sticks across the papers or sprinkling on soil before wetting is also helpful.
    The best paper mulch is made of shredded paper. A five- to eight-inch-thick layer of shredded paper will quickly mat down to a one-quarter-inch layer that will easily stay in place after being saturated with water. By fall, the paper will have disintegrated, leaving little to no residue.
    Mulching-grade black plastic not only controls weeds but also conserves moisture. It is best applied soon after tilling the soil and before trans­planting. When transplanting, simply cut an X with a sharp knife for plants. Where seeds are to be planted, the black plastic mulch must be applied after the seedlings have emerged. Anchor the edges of the plastic with soil immediately after it is laid.
    Reflective mulches do a three-fold job: preventing weeds, reducing water loss by evaporation and repelling insects. Aluminized paper or plastic mulches are used primarily in growing squash, cucumbers and melons to repel the stripped cucumber beetle. The light reflected by the aluminum is polarized, confusing the insects as many navigate using light waves of different length. Reflective light also increases the amount of chlorophyll on the underside of leaves it reflects on. An early study with reflective mulches on tomato plants reported a one-third increase in chlorophyll in leaves, with most of the increase on the under side nearest the reflective light source. Several gardening catalogs advertise red mulch for under tomato plants.


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