Finish pruning up your trees and shrubs this week

The cool days of late March and early April offer a great chance to finish pruning your trees and shrubs.

When pruning large limbs off trees, begin with an undercut first. This is a cut from the bottom up, about one-third of the way through the limb, 4 inches or so away from the main trunk. Make the next cut from the top, an inch or so outside of the undercut, to remove the limb. The undercut keeps the limb from splitting and breaking off, which could damage the trunk. Do not cut flush to the trunk, but just outside the branch collar at the base of the branch. Look for the point where the branch is enlarged close to the main trunk of the tree. It’s generally not recommended to paint the wound caused by pruning. For the best results, be sure to use a sharp saw.

Most evergreens will not respond well to being aggressively cut back. A good rule of thumb is to avoid cutting beyond green foliage. Yews, though, will respond to a more drastic cutback into old wood — but be patient, as they may take two to three years to completely fill in. The more aggressive the pruning, the longer it will take. Consider how long you’re willing to wait for the shrub to look full again, or do a more gradual reduction over a few years until you reach your goal. It’s best to finish pruning before the new growth begins in early spring.

Protect emerging tulips

Now is also a good time to protect emerging tulips from deer and rabbit damage by spraying with a repellent or covering with netting. Repellents will need to be reapplied after rain. Netting will need to be adjusted as bulbs grow and may need to be weighted down to keep from blowing away. Deer and rabbits typically do not eat daffodils and ornamental onions, so there’s no need to protect these plants. The Chicago Botanic Garden staff has used blood meal as a repellent with some success, but you may want to experiment with other repellents to find what works best for your garden.

Cool your heels on annuals

It’s been a long winter, and most gardeners are anxious for some color, but consider waiting to plant any annuals. I saw some pansies for sale a couple weeks ago — too early for planting them out in the garden. Monitor the longer-range weather forecast before planting; even pansies, one of the more cold-tolerant annuals, will be damaged when temperatures get to around 25 degrees Fahrenheit if they’re left uncovered.

If you want to have some things out early, keep them in a pot and bring them inside on very cold nights. The temperature threshold as to when to cover a plant or bring it in will depend on the type of plant, but as a general safety measure, cover most plants when temperatures are predicted to drop to 28 degrees Fahrenheit or lower. Some plants for sale in early spring will be more cold-sensitive and will need to be covered as temperatures drop to freezing.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.