As Summer Winds Down

Friday, August 19, 2011

We’re still having hot days, but the nights are longer and cooler, refreshing plants as well as people.  It’s still a bit early for lawn renovation and installing new plantings; those tasks are better done in September and October.

You may notice insect damage on your ornamentals now. Don’t reach for the sprayer first! First, ask if the damage really matters to the health of the plant, or is it just cosmetic — or is it too late to do much anyway? By now the leaves on the plants have done most of their work for the season. If they get a little chewed it’s not going to harm the plant’s health much.

Of course, cosmetic damage is real damage too, because it gets in the way of enjoying your garden. The remedy is to prune out branches of shrubs that have been made unsightly.  (Delay real pruning until dormancy in November or later.)  Cut back perennials whose leaves are fading anyway.  In my garden, I’ve cut back some daylilies whose leaves were drying out from the drought. They will come roaring back in the spring.

If you have irises that are getting crowded, now is the time to dig and divide them. Enrich the soil with compost, and replant the healthiest young rhizomes (the thick horizontal roots), giving them some room to spread and watering to establish them.  Plant the rhizomes so that their tops show just above the surface of the soil; don’t bury them. If some of the rhizomes are mushy they’ve probably been damaged by iris borers and should be destroyed. Cut back the leaves to about 3” high.  Those old leaves have done their job and the plant will soon make new ones. Don’t mulch your irises, but do remove dead leaves and trash from around the plants.  Iris borers are the worst pest of irises, and depriving them of places to hide and lay their eggs is the best form of control. Sprays don’t help because the borers spend most of their lives inside the plant.

When deciding where to plant your irises, make sure there’s plenty of sun for good bloom, and that it’s not a wet spot — they like good drainage. Then remember that their time of peak beauty is a few weeks to a month. After that you have the blue-green sword-shaped leaves for the rest of the summer. These can be very decorative when played off against plants with different leaf shapes. And if the iris leaves get beat up in late summer don’t be fearful about cutting them back to a few inches high.

By guest blogger, Jessica Milstead

Jessica has been a Charles County Master Gardener since 2002 and is certified to evaluate gardens and landscapes for their adherence to Bay-Wise principles.

Photo courtesy of Craig Renner