by Mary
Sellers
Colorado State University Cooperative Extension
Master Gardener
Larimer County
Q. Everyone had nice lilacs this year except me. The bush in my yard is old; is that why it didn’t bloom?
A. There are many possibilities why your lilac didn’t bloom. Tender young buds could have been damaged by frost. Older lilacs benefit from being thinned (removing older, thicker branches). Make sure that you don’t remove more than one third of the shrub when you prune, as heavy pruning could stress the plant. If you trimmed your lilac in the fall you likely removed all the flower buds. The best time to trim lilacs is after they bloom in the spring.
Q. My iris look like one big clump, can I divide them now?
A. Iris needs to be divided every three to four years. You can divide iris any time after they have bloomed, but most people wait until the first part of August, when the leaves yellow. Waiting allows the rhizomes (underground stems) of iris to collect energy and nutrients from leaves from photosynthesis. When you dig iris, you will see the rhizomes form notched areas, a good place to break them apart. It is also common to see new leaves in these sections. The older sections of the rhizomes show age by being wrinkled or shriveled and can be discarded. Replant the newer sections in a large space. When you plant iris, leave the top one-third of the rhizome exposed above ground. Fertilize iris in the fall with bulb fertilizer.
Q. What are those big clumps of yellow and pink flowers that look like groundcover I see all over town?
A. This time of year, the yellow is most likely baskets of gold (Aurinia saxatilis). They pink clumps may be creeping phlox (Phlox subulata). There are many new varieties of spring-blooming groundcovers. See Fact Sheets #7.405 “Herbaceous Perennials” and #7.230 “Xeriscaping: Ground cover plants.”
Gardening and Insect Fact Sheets are available on-line by clicking HERE.
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