Mulch provides many benefits to plants and soil: insulation, shade, moisture retention, weed reduction, and soil building. But when mulch is applied at the wrong time or in the wrong form, it can do more harm than good. Use the following guidelines to get the greatest benefit from your mulching effort.

First, make the most of your garden space, moisture, and organic matter (including mulch) by planting wide rows - a width that you can comfortably reach across, rather the width of a single plant. Wide row planting reduces the number of paths needed through your garden, and keeps more of the soil surface covered. This results in fewer weeds and better moisture retention, so your mulch can be applied where it is really needed.

~~Finished Compost Mulch~~

There is no bad time to add finished compost to the soil, but for maximum value from this black gold the best time is shortly after spring shoots and seedlings have gotten established and have their true leaves. Apply a layer of finished compost mulch. Often called a top dressing, this layer will merge with the topsoil quickly, but try to keep the compost from touching the plant stems anyway.

How thickly you layer the finished compost mulch depends on how much you have available and how much ground you have to cover. Even a thin layer is beneficial; it provides nutrients that gradually work their way down, and gives some protection against weeds, temperature extremes, hard rain, and so forth.

~~Partially Composted Material~~

Half-finished compost or compost that is noticeably fibrous is never good for mulching plants, or even for adding to the soil near growing plants. Separate additions of partially composted material from planting by at least two or three weeks. The best time to add this kind of compost is in October or November in ground that will be allowed to rest.

Soil bacteria will break down the material, but these organisms have to use nitrogen in order to do their work. Eventually, the microbes will release the nitrogen and make it available to plants again, but in the meantime, the half-finished compost has the effect of starving rather than feeding any growing plants.

~~Hay and Straw~~

Apply a layer of straw or hay once plants are beyond seedling stage. The timing also depends on soil temperature. Since this mulch forms an insulating layer, wait until the soil is warm; else the layer of mulch will insulate in the wrong way-preventing the soil from warming up.

In addition to the straw or hay forming an insulating layer and helping retain moisture, the mulch becomes a nice resting place for melons and squash.

Straw is more carbonaceous than hay, and will break down more slowly. Hay often has a moisture content, and will break down faster. Both are good mulches, but if slugs and snails are a problem, straw is better. Again, keep the mulch back from touching the plant stems.

~~Leaves and Grass Clippings~~

I prefer to compost leaves and grass rather than use them as mulch. Leaves are generally acidic, and affect the ph of the soil. However, some plants such as raspberries prefer slightly acidic soil, and for plants that don't like an acid ph, an amendment of lime could help neutralize the effect of the leaves.

Grass clippings can be very effective mulch - especially for moisture retention, but keep an eye on it. Grass packs down, preventing air circulation so that anaerobic decay occurs. Again, I prefer to compost grass; turning the compost keeps it aerated.