Replacing rock around tree, Overwintering new spruce trees
Q: I have a large maple tree surrounded by river rock. I put black plastic around the tree about 15 years ago before putting the rock down. It looked great until the last couple of years. The rocks have shifted and some of the plastic has worn down. It looks pretty shabby. I don’t want to take all that time and energy to remove the rock and the plastic just to put it in again, especially as it didn’t last as long as I thought it would. What’s another weed barrier I can use around my tree that will look nice?
A: River rock atop black weed barrier is a popular choice around trees, but how about bark mulch instead? Black weed barrier and river rock do not provide a healthy environment for trees.
Both materials absorb and trap heat in the summer, increasing heat stress for the tree and making it more susceptible to life-shortening tree health issues. Black plastic also impedes water flow to the tree roots.
Organic mulch, on the other hand, has a myriad of benefits for your tree and you: Not only does it reduce weed pressure and therefore keeps the mower and string trimmer away from injuring your tree’s trunk, but mulch conserves soil moisture and breaks down over time to improve the soil nutrient balance.
Your tree will do best with a mulch layer of 2-4 inches under the dripline of the tree (the ground area between the trunk and the outer edge of the lower branches), but don’t hug the trunk with the mulch. Leaving a gap of 1-2 inches between the trunk and the mulch ring reduces rodent damage in the winter and moisture injury to the root flares during wet seasons.
Many materials can be used as mulch, but bark mulch— with its coarse, dark wood chips—is an attractive landscape material that can rival the aesthetics of river rock.
Q: Last fall, I planted a windbreak of 90 Norwegian spruce trees. I staked them all, wrapped their trunks to protect against frost crack, and put a wire cage around each to protect against deer damage. None of them made it through the winter. In November, I have 90 replacements coming. What is the trick to getting them to survive through the winter?
A: November is a little late to plant new trees. The ideal time to plant trees in the fall is September and October so they have enough time for their roots to get established before going into dormancy and enduring a long, dry winter.
If you can, bump up the planting date for this year’s windbreak replacement. While staking can be helpful and protecting the trunks against winter wildlife damage is important, we need to keep in mind that the winter months are not only cold but dry.
Cold air is dry air, and winters with low precipitation amounts—as happened during last winter—are as bad of a drought for young trees as droughts that occur in hot, dry summers. Mulching can help conserve soil moisture around new trees, but it’s vital that your trees get enough water through the winter.
Aim to water your trees one inch of water one to two times monthly when the daytime temperature is at least 40 degrees Fahrenheit. Apply water slowly so that moisture reaches the tree’s roots. Water at midday and, when short on time, focus on the driest areas such as trees that catch a lot of wind or trees growing on a south-facing slope.
It’s important not only for your irrigation equipment but also your trees that the ground not be frozen when you’re watering; frozen ground doesn’t allow water to soak in, and tree roots cannot uptake water when there’s ice in the soil. Use an empty tuna fish can to measure water output; check to see how far into the soil profile that water is seeping by pushing a longshank screwdriver into the ground near the tree. Dry soil is hard soil; if you can push a screwdriver easily into the soil, adequate soil moisture is likely.
Some evergreens can be prone to winter desiccation, which means death by drying out. There are products called anti-desiccants, or anti-transpirants, that cover conifer needles with a waxy layer to trap in moisture and provide a barrier against moisture- wicking wind. While anti- desiccants can help, they do not replace planting not too late in the season, mulching, and regular watering through a dry winter.
Rita Brhel lives in Fairfield, has a Bachelor of Science in Agricultural Sciences and Natural Resources from the University of Nebraska- Lincoln, is a certified Master Gardener and Master Naturalist trainee, serves with AmeriCorps in environmental education, and coordinates the Horticulture Program at the Adams County UNL Extension office in Hastings.
Have a horticulture question? Contact your County Extension office to get connected with your local UNL Extension horticulturist.
