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Spring is better for hydrangea pruning

The best way to prune hydrangeas depends on the type, such as this Hydrangea arborescens type, left, or this Hydrangea paniculata type with pyramid-shaped flower clusters, right. Special to Forum News Service

Q: What's the best advice for pruning hydrangeas, as I have six very large plants. Can I trim them down this fall? — Sharon Dubois.

A: The pruning method of hydrangeas depends to which of the two well-adapted types they belong. Hydrangea arborescens types, like Annabelle with the large, round, white flower clusters, grow from near ground level each spring, so the dead above-ground branches are best pruned back to 6 inches or less each spring.

The Hydrangea paniculata types, with pyramid-shaped flower clusters like the popular Vanilla Strawberry, grow like "normal" shrubs, leafing out from the upper branch structure each spring, rather than dying back. Pruning consists of shaping and size control, rather than drastic cutback.

Pruning on both types of hydrangeas is better accomplished in spring before new growth begins, instead of fall. Will fall pruning kill a hydrangea? Certainly not, but if the upcoming winter is unusually cold with little protective snow, hydrangeas tend to winter better with branches left intact until spring.

Q: I planted a Purple Prince Crab on the south side of my house. This is the second or third season, but I've had almost no blossoms. Today I found a grand total of nine tiny normal-looking crab apples. What can I do to encourage this tree to bloom? — Les Hazlett, Fargo.

A: It's not unusual for an ornamental crab apple to take three to five years after planting to begin full bloom. The trees are often flowering in the pot if purchased in spring, but after planting, the tree switches to grow-mode and begins rooting out into the soil with a young-age growth spurt. Flowering is delayed during a few years of active youthful growth.

Ornamental crabs and "eating apples" are closely related, and it's not uncommon for their early youthful years to be foliage-only. Eating-type apples average three to seven years from planting until flowering and fruiting.

One thing that can be done to prevent flowering delay is to avoid lawn fertilizer over the tree's root zone. Lawn fertilizer is high in nitrogen, promoting green foliage growth at the expense of flowering and fruiting. Tree roots extend outward from the trunk at least as far as the tree is tall. For example, a young 8-foot-tall crab apple tree's roots extend outward at least 8 feet from the trunk in all directions, usually farther. If lawns are fertilized, this rootzone circle around the tree should be avoided.

Q: I have fruit fly-looking insects on my prayer plant. I sprayed the plant with soapy water and put it in a bag. They seem to be multiplying. Any suggestions? — Sue Uhlir, Fargo.

A: If the little black insects are flitting around, they're probably fungus gnats. A good solution is the product called Mosquito Bits, which might sound funny, but the label also indicates its use for fungus gnat control. The granules are spread on the soil following label directions. It's sold at national chains and some locally-owned garden centers.

Mosquito Bits contains a strain of the organic insect control Bacillus thuringiensis, which kills the fungus gnats in their small, larval stage as they live in the potting soil.