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Ask the Master Gardener: How much mulch is too much mulch?

An example of an incorrect way to mulch a tree. Photo by Jennifer Knutson

Dear Master Gardener: When protecting trees from rodents, what is hardware cloth and how far out from the tree trunk should it be? Can I use plastic tree guards instead? Also, how much mulch should I put around my trees this spring?

Answer: Hardware cloth is a type of garden fencing that has ¼ or ½-inch squares and is made of galvanized steel. The U of M recommends placing a ring of hardware cloth around the tree about six inches from the trunk. This can be kept on year-round. When putting the hardware cloth in place, make sure there are no gaps between the bottom of the mesh cylinder and the ground where animals could crawl under the fencing. Plastic guards are also effective for small trees, but make sure to take them off in late spring because the plastic could cause the trunk of the tree to stay moist. Diseases such as fungal canker diseases (rots), bacterial attacks or virus diseases can more readily penetrate to the interior of the plant when the bark remains continually moist.

It is extremely important to keep mulch away from the trunks of trees. Sometimes you see volcanoes of mulch around tree trunks. This can have an adverse effect on trees. Wood-boring insects living in the mulch can tunnel through to the softened, partially decomposing bark and introduce disease. If tree trunks are not protected with a physical barrier, mice and voles can tunnel through the mulch and chew through the outer bark to reach the delicious living inner bark, which will cut off the flow of water up from the roots and nutrients down from the leaves, causing the tree to die. Roots searching for oxygen tend to migrate up toward the top of the mulch layer, then dry out when summer drought sets in. A thick volcano of mulch can prevent rainfall or irrigation water from reaching the root system, causing plant stress.

Instead of making a volcano of mulch, make a donut. Using an organic mulch, make a ring about three to four inches deep, going two to three feet out from the trunk or to the canopy's drip line. Leave two to three inches from the trunk to the mulch. This ring of organic mulch will help maintain tree health by aiding in water retention, inhibiting weed development, protecting from lawn mowing equipment, offering a layer of insulation during cold weather and adding organic matter to the soil. It is important not to have mulch up against the trunk of a tree!

Dear Master Gardener: What apple trees grow best in Crow Wing County?

Answer: The Agricultural Experiment Station, near the Minnesota Landscape Arboretum, was created in 1887 with the goal of developing apple trees that could survive our cold, harsh climate. The University of Minnesota has developed some outstanding cold hardy apples, with the Honeycrisp being the most famous. Honeycrisp apple trees have a USDA Zone 4 rating. The majority of Crow Wing County is in Zone 3b (cold hardiness to -35 F.), but there is a little section of the southwest part of the county that lies in Zone 4a (cold hardiness to -30 F.). This past winter we saw temperatures dip to -40 F., which would mean plants need to have cold tolerance to Zone 3a.

You need to have at least two different cultivars, or a crabapple tree, within 100 feet of each other in order to get fruit. All trees listed below are hardy to USDA Zone 3.

• Zestar trees were developed by the U of M and released in 1999. The tree is vigorous, upright and very susceptible to apple scab. The fruit ripens in late August to early September. The most outstanding feature of a Zestar apple is its sweet-tart taste with a hint of brown sugar. It is juicy with a light, crisp texture and maintains its great taste and crunch for two months in refrigeration.

• Haralson was introduced in 1922 and is a tree of low vigor. The fruit has a firm texture with a complex tart flavor that is good for both eating and baking. It is a late season apple and the fruit will store for four to five months. It has a tendency to be biennial, bearing every other year, and the fruit is prone to russeting (a brown, corky tissue on the surface of the apple).

• Haralred is extremely hardy and fire blight resistant. The dark red fruit is juicy, tart, firm and keeps well. The fruit ripens in September to early October.

• State Fair, introduced in 1977, ripens mid to late August. It has striped, red, juicy, moderately tart fruit good for eating and cooking. The fruit will store for two to four weeks. The tree is susceptible to fire blight and can be prone to biennial bearing.

• Sweet Sixteen was introduced in 1977. The tree is very vigorous, but the fruit can be subject to premature drops, which makes it a somewhat finicky tree to grow. It is worth growing because if you can get the fruit to peak ripeness, it has an amazing, unique flavor. The fruit is crisp and juicy with a very sweet flavor that tastes like sugar cane or cherry candy. The fruit ripens mid to late September and stores for five to eight weeks.

• Fireside was introduced in 1943. It is a vigorous tree that has large fruit with a sweet flavor. It is an old-fashioned dessert apple.

• Frostbite is a noncommercial variety that is extremely cold hardy. Grafting began in 2008 and the trees were ready for sale to homeowners in 2009. It is a grandparent of Honeycrisp and parent of Sweet 16. If you want a unique eating experience, it has an unusual flavor that tastes like concentrated fruit punch. Biting into a Frostbite apple is like biting into a piece of sugarcane. It is a late season variety that is quite small in size, about 2-1/2 inches in diameter. It is excellent for cider and those with a sweet tooth.

Dear Master Gardener: My neighbor recommends a natural weed killer using Dawn dishwashing detergent, vinegar, and Epsom salts. Good idea or not?

Answer: Not! There is nothing natural about it—look at the ingredients list for Dawn! Vinegar and Epsom salts are both chemicals and neither one is good for soil health. Vinegar will kill the leaves of weeds, and anything else it lands on including beneficial insects and amphibians, but doesn't kill the roots, so most of the weeds will be back in about a week. Concoctions that have not been tested and labeled as herbicides are technically illegal and should not be used. Fully tested commercial herbicides, used in the correct amounts and with proper application, are actually cheaper, more effective, and safer for you and the environment.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.