Cut back perennials, roses this month
Finish cutting back perennials and cleaning up garden debris this month. It is best to cut back perennials before they start growing to minimize damage to the new growth.
Many perennials have started growing by now, so be careful as you are working. It can be hard to see new growth on ornamental grasses, so be sure to cut them back before consistent warm weather sets in later in the month.
If the weather warms up and the grasses are growing, cut them at a few inches above the ground to avoid the new shoots. Be careful of any bulbs that have started growing.
Gently press back any perennials that have heaved out of the ground over winter. There is a greater chance of frost heaving in late March and early April. The freeze-thaw cycle in spring can push recently installed plants out of the ground if they were not mulched the previous year. Avoid walking in garden beds when soil conditions are wet to minimize soil compaction.
• Begin uncovering hybrid roses if you have not already done so by carefully removing mulch from the base. A bamboo stake works well for this task.
Leave a small amount of mulch at the base for protection in case of a late hard freeze.
Prune roses back to live growth, which in some years may leave only 1 to 2 inches of stem.
• It is time to begin spraying crabapples that are susceptible to apple scab (typically, this disease affects older varieties of crabapples) when the buds are starting to open. If your tree's leaves become covered with black spots and fall off in late summer, they can benefit from a protective spray program or should be replaced with a new, disease-resistant cultivar.
Begin spraying after the buds open and treat once every seven to ten days until the leaves are fully open (generally, three treatments suffice). Proper timing of the spray treatments is very important for them to be effective.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.