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Gardening in Minnesota is challenging. We get the itch to plant early in the season while the ground is still cold and the temperatures vary from frost to hot. As I write this it's only a month since our average last frost date. Already summer's here with long warm days that are becoming downright hot. Our vegetables and flowers are growing fast and so are the weeds.

We've been hoeing and pulling weeds all through May and June. Most of us don't have the space to use a tiller for weed control and so we hoe, hoe, hoe. Then one day it's just too hot to hoe! The solution? Mulch the vegetable garden and the flower beds, too.

Mulch is defined as any substance used to cover the soil. Mulching does several good things. It reduces water evaporation, so plants don't dry out as fast. That means a steadier moisture supply to the plants with less watering. Mulching also prevents weeds from germinating by blocking the sun's rays from reaching the ever-present weed seeds. That means less weeding.

Mulching can also increase biological activity in the soil, especially mulches that can be tilled in at the end of the season. Reduced soil erosion is another benefit as the mulch holds the topsoil in place.

In summer mulching shades the soil keeping the root zone cool and causing less stress to plants on hot days. Mulch can also be used to temper the effects of winter's cold, but that's a subject for another season.

So what do we use to mulch the garden? There's a wide variety of organic materials as well as inorganics like plastic.

Black plastic blocks light and suppresses weeds while raising the soil temps 3 to 6 degrees. Clear plastic can raise the soil temps much higher and is used in the spring to warm the soil for earlier planting. However clear plastic doesn't block out the sunlight and so weeds can become a problem if it's left in place. In recent years some research has showed some benefit to mulching tomatoes with red plastic. Supposedly it increases yields. That's one I haven't tried.

Bark and wood chip mulches work well for permanent mulch around shrubs and trees and perennial beds. Used around the base of trees they must be several inches thick but kept away from contact with the trunk. A landscape fabric of woven plastic can be used underneath to block weeds while permitting water to flow through.

More commonly used garden mulches are organic materials that can break down over time on the soil surface or are tilled in at the end of the season and add fertility to the soil. Leaves, especially chopped, are excellent, whether with newspaper underneath or not. Finished compost and well-composted manures add nutrients while they mulch. Sawdust, or other fine materials like lawn clippings, work well for tiny plants. Cocoa bean hulls are known to repel deer from susceptible plants like hostas but must be refreshed often. Even radish tops or freshly pulled weeds that have not gone to seed can be placed on the ground for mulch. Straw, old hay, peat moss all can be used as mulch.

Grass clippings are readily available to most of us, but there are some cautions if you are going to mulch with them. They must be free from chemicals such as weed killers. Also avoid clippings with abundant weed seeds. Spread thinly; more than a few inches can cause matting and fermentation, which produces odors and prevents oxygen from getting down into the soil. That smelly fermentation, however, may also repel deer.

In my garden tiny things like baby onions are mulched with sawdust from my husband's workshop. We've also used ground corncobs, which are hard to come by these days. Bigger row crops are mulched with overlapping 2 or 3 sheets of newspaper (only black and white, no color) covered with a few inches of leaves. The asparagus gets leaves without the paper underneath so that new spears can grow through.

One thing I don't mulch is squash and pumpkins since they put down new roots as they grow and mulching would interfere. We mulch everything else, even potatoes. "What, you mulch potatoes?" asks my friend. I do. I've found newsprint under leaves does several things. It keeps the developing potatoes protected from sunlight, so they don't turn green, and ensures a steady supply of moisture while keeping the roots cool, which potatoes like. And I never have potato beetles to worry about.

Mulched tomatoes are healthier, too. Protecting the plants from backsplash from rain or watering prevents blight caused by soil-borne fungi. Ensuring an even supply of moisture keeps my tomatoes free from blossom-end rot and prevents cracked fruit, too.

We mulch for all the above reasons plus one more. Once the garden is mulched all we have to do is watch the garden grow, pick the vegetables and the raspberries, and enjoy the flowers. And that's what I like best about mulch.

Master Gardeners will again be at the Historical Society Log Cabin during the Chisago County Fair in Rush City, July 16-20 doing demonstrations and answering questions.

For more information on the U of M Extension Service web page go to www.extension.umn.edu and search. Or, you may call our Yard and Garden Line anytime and leave a message at (612) 624-4771. A Master Gardener will return your call. The Master Gardeners also staff the Extension Office on Monday from 4:30 to 8 p.m. Call (651) 674-4417 or drop in with your samples and gardening questions.

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