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Published June 28, 2009, 12:00 AM

DARREL KOEHLER: Mulch can be a gardener’s best friend

Warm summer weather finally has arrived which means it’s time to mulch our gardens. Summer mulch, which can range from well-rotted compost to a wide variety of other plant materials, is said to be the gardener’s best friend. We agree.

By: Darrel Koehler, Grand Forks Herald

Warm summer weather finally has arrived which means it’s time to mulch our gardens.

Summer mulch, which can range from well-rotted compost to a wide variety of other plant materials, is said to be the gardener’s best friend. We agree.

Some of the reasons include: Mulch reduces plant stress by cooling the soil. It help keeps the soil moist so you don’t have to water so much. Mulch keeps the weeds at bay by depriving them of the light they need to germinate.

Growing up on a farm in Minnesota’s Otter Tail County, we had lots of mulch materials. Sawdust and wood shavings were readily available and worked especially well in strawberry beds and raspberry patches. There was lots of well-rotted manure as well as straw. And, of course, mounds of well-rotted leaves and garden debris.


Now, the choices are more limited. Well-rotted compost — a favorite — works well as mulch for a season. It then can be turned back into the soil as an organic fertilizer. Gardeners have been composting for centuries to increase organic matter in their soils as well as to provide essential nutrients for plant growth.

Aeration, moisture, particle size and fertilizer are the four main requirements needed f or proper composting. Your pile should be loose and well-mixed. If adequate rainfall becomes a problem, a few minutes with a garden hose will solve the problem. Small pieces will decompose faster, so keep a hand pruner at hand. Grass clippings are generally high in nitrogen and will aid in composting.

Clean straw works well for strawberries or raspberries. If you use lots of straw in your strawberry bed, you can crawl on your knees when picking with out getting dirty. Well-rotted straw works well for summer mulch, too. You can purchase bark, wood chips and cocoa bean hulls. However, if you have dogs, skip the cocoa bean hull mulch which can prove fatal if ingested

Gravel, pebbles, lava rock, field stone or crushed rock are a more permanent form of mulch. It is best to apply a heavy landscape barrier before placing the material. This will keep down the weed problem. Plants may require extra watering as the barrier will limit rain from penetrating. There also can be heat buildup with stone. Leaves and other debris can be difficult to remove from between rocks. Weeds can sprout from decomposed debris, too.

Garden tour

Tickets for the 25th annual Grand Forks Horticulture Society garden tour, July 18-19, are on sale. Outlets are All Seasons Garden Center and Floral, Tim Shea’s Nursery Inc., both in Grand Forks, Wagner’s Landscaping Inc., Fisher, Minn., Hardware Hank, East Grand Forks, and Roger’s Garden Korner in Warren, Minn. Tickets are $10 and are good both days as well as the plant sale and gardener’s garage sale at the Myra Museum in Grand Forks. Proceeds go toward a variety of group-sponsored garden projects.

Anne Smith, spokeswoman for the group, says six gardens have been tentatively signed up for the event. Three are in Grand Forks, two are in East Grand Forks and one is in Warren. The gardens selected are both new and ones that drew attention in previous tours. Questions may be sent to

Tomato tips

Despite the weather woes, especially below-average temperatures readings, tomatoes are making good progress. Mulch tomato beds to reduce problems with early blight, a fungal disease that causes lower leaves to develop yellow spots that expand. On diseased plants, remove afflicted leaves and spray with a fungicide approved for use on edible plants. By applying something as simple as grass clippings, you can prevent disease-laden soil from splashing onto tomato foliage.

Another frequent tomato query is what causes the deep cracks and fissures that form on the t ops of tomatoes. These are actually growth cracks and are associated with abundant moisture — rain or irrigation — after a dry period. Abundant water causes the tomato to grow more rapidly than its skin can expand, so it splits or cracks. Keep tomato plants evenly water and you will prevent this problem.

Terrain change

A frequent question from gardeners is if they can change the contour of their yard by adding soil and placing it over the drip area of shade trees. This is a particular serious problem if you plan to do so with an oak. For the sake of the tree, you should never pile soil over the existing tree roots, most of which can be found in the top 12 to 18 inches of soil. By adding soil over the root zone, you are reducing the amount of oxygen that reaches the roots. Even a few inches of soil can have a damaging effect on tree species that are especially sensitive to changes in their environment.

Spruce problem

Another common woe is what to do with the ground area around the base of large evergreen trees, such as spruce. While ground covers may be one answer, you will have to select several different kinds of shade tolerant plants as well as proving supplemental water and occasional fertilizer. An easier way to deal with this common problem is to get rid of the turf grass in a circular swath directly around the tree. Then apply a 3- to 4-inch deep layer of organic mulch such as wood chips or ground tree bark. This will help keep the root zone moist and prevent the grass from competing for water and nutrients. It’s also a good to prevent mechanical damage to the trunk by lawn mowers or weed whackers.

First frost

With the late spring, many gardeners are concerned if garden vegetables will mature in time to beat the first frost, which normally occurs in late September. This is a special concern if they have been forced to reseed. While we are running 10 to 14 days behind normal, warm, sunny weather should reduce this time lag. According to folklore, the first frost comes six months after the spring’s first thunderstorm.

While we have had few severe thunderstorms, there were some thunder boomers in late March or early April, so we are about on track for a September frost. Early maturing veggies, such as snap beans, peas, lettuce, Swiss chard and beets can be safely planted yet as well as carrots, kohlrabi and greens. However, time is getting short for melons, sweet corn and winter squash. But if we have a late frost, they should make it, too.

Kudzu invasion

A Grand Forks gardener who traveled through the South recently has a query about those vines found everywhere. It’s the dreaded kudzu vine, originally brought to this country from Japan a century ago. A member of the pea family, it was intended for either soil stabilization or livestock forage. Instead, it has become a terrible problem and is known as the vine that took over the South. It can grow up to 60 feet a year and is an out-of-control nuisance. Fortunately, it won’t tolerate our severe winters.

Koehler is the Herald’s garden columnist. His column is published every Sunday in this section during the growing season. Send garden questions to him in care of the Grand Forks Herald, Box 6008, Grand Forks ND 58206-6008. Tune in the weekly gardening show airing at 4:10 p.m. Thursdays on KNOX Radio 1310 (AM).