by Margie Siegal
Mulch can be a lot of different things, from straw to high tech plastics, but basically, it is anything you put on top of the soil your plants are growing in to help them along. There are almost as many reasons to mulch as there are kinds of mulch.
Your aim in going through the work (and sometimes expense) of putting down a layer of mulch depends on what climate you live in. If you are in northern Minnesota, a layer of air trapping straw can extend your growing season long enough to actually harvest something. Here in Zone 9 Alameda, we don’t have to worry about frosts (or moose trampling the strawberry patch) but we do need to worry about drought, tenacious weeds, and keeping the soil warm despite the fog rolling in at 6 PM. Mulches will help with all these problems.
Alameda Gardener’s Reasons to Mulch
Conserving water: The first, second and third reason Alameda gardeners want to put down mulch is to make the most of scarce and expensive water. Many of us are gardening on sand dunes. Water goes right through the soil, making it difficult for thirsty plants to grab enough to thrive. If in addition the afternoon sun evaporates what is left, either plant survival will be in doubt or you will be watering all the time. Putting down mulch will keep the soil moist without fear of sternly worded letters from East Bay MUD.
Discouraging weeds: Unlike the plants that you are trying to grow, weeds thrive in the Alameda climate and sandy soil. Cutting off light to most weeds will keep them from out competing your veggies. However, there are some weeds, such as Bermuda grass, which will simply grow underground until they find a light source. Despite what the promotional literature says, don’t expect miracles.
Warming the soil: Mark Twain did NOT say, “The coldest winter I ever spent was summer in San Francisco,” but he should have. Unless you have a favorable micro-climate, peppers, tomatoes, eggplant and melons need help. A mulch can absorb heat and serve as a blanket for the roots of heat loving vegetables.
Kinds of Mulch
There are a lot of different kinds of mulch, and the following list contains just the more popular items people use. Basically, there are two types of mulch: the kind you rake (bark chips, chopped straw or hay, compost, and similar items) and the kind you unroll (various proprietary types of paper or plastic) Each type has pros and cons.
Bark chips or shreds: Bark is usually used around shrubs and landscape plants, and can really dress up a yard. It is also good for marking paths. Experts suggest putting down 2-4 inches of bark.
Bark will keep the ground moist and has the potential for sticking around for several years, cutting expense and work. On the other hand, if you put bark in the same area as your trees, make sure you keep the mulch at least six inches away from the trunk. Mulch against a tree trunk invites rot and un-beneficial insects. Bark will only slow down the tough weeds of Alameda, most of which will grow right through it, so don’t expect bark to keep you from weeding.
Compost: Finished compost looks like soil, is dark brown and has a pleasant, mild odor. It will provide some nutrients and add organic matter to your soil, as well as keeping the soil from drying out. Just add an inch or two around your plants.
Hay and straw: Both are available from feed stores. Hay is horse and goat feed, straw is coarser and is used for bedding for your sheep, pony or unicorn. An inch and a half of either, chopped roughly, over your garden bed will slow water evaporation and warm the soil. CAVEAT: As hay or straw decomposes, it will pull nitrogen from the soil, so if you decide to use straw, spread a high nitrogen fertilizer, such as fish fertilizer, first. Both hay and straw may harbor weed seeds – be forewarned.
Newspaper: Newspaper may be unsightly, but it is free, and it works. I have found that the only way I can get carrots started is to put down a row of carrot seed, cover with an eighth inch of soil, wet the soil, put down two or three sheets of newspaper and soak the newspaper. The newspaper keeps the soil moist and can be removed after the carrots sprout.
Paper mulch: Rolls of paper mulch are sold under various trade names. I use Weed Guard Plus, which guards against evaporation and warms the soil a few degrees – enough to raise melons in Alameda. I run a drip irrigation system under the paper. The stuff is listed for organic cultivation and biodegrades slowly. Despite the name, it does not guard against tenacious Alameda weeds, which just grow around it and poke through the holes I cut for my transplants.
Plastic mulch: Plastic mulch is often used by commercial farmers. Most types do not biodegrade (check the label, some do), and can be rolled up at the end of the season and reused. Plastic mulch comes in black (used to warm up soil and deter both evaporation and weeds), red (proven to increase tomato yields) and clear (best soil warmer, but does not deter weeds).
Don’t Mulch with These:
Anything that might be contaminated with pesticides or herbicides: Unfortunately this includes municipal compost. There is no way to find out what is in it.
Anything that might be contaminated with plant disease causing organisms You don’t want your plants to get sick. Don’t put diseased plants in your compost pile – put them in the green bin.
Plastic flamingos or garden gnomes: They won’t help your plants at all.
How to Mulch
Prep the soil: Weed and break up the surface (a hula hoe will do both jobs at once if you have one). Water well. Add nitrogen rich fertilizer if you are going to be mulching with un-composted organic matter.
Mark off where you want to mulch: The kind of mulch you rake should be kept six inches from tree trunks and only used as a side dressing for young plants. Once the veggies are established, you can move the mulch closer. Plastic and paper mulch can be laid down and holes cut for transplants.
Get your wheelbarrow and start laying down mulch. There really isn’t much more to it. Plastic and paper mulch should be in contact with the soil to have the most impact. Hold down with soil, pieces of brick, stones, broken pots or staples specially made for the application
For more information in a handy pocket size volume: How to Mulch (Storey Publication, 2015) by Stu Campbell and Jennifer Kujawski.