We moved into a new house last spring, and there is an old clematis vine scrambling up and along a fence. It bloomed fairly well last year, but it looks to me like it needs some pruning – it has some pretty scraggly-looking sections in it. I don’t know what variety it is. How and when should I go about pruning it?

Clematis can be a confusing group of plants to prune, since they vary in flowering times, and therefore are not all pruned the same way. They are generally divided into three categories: clematis that flower in spring require little pruning (pruning group 1); those that flower in early summer require light pruning (pruning group 2); and those that flower from midsummer onward require hard pruning (pruning group 3). Without knowing which category your plant falls into, you may want to just do some renovation pruning this year, by removing most of the old, scraggly-looking growth, and retaining a few good long shoots. These may need fanning out and retraining, but your clematis should flower at some point during the summer, helping you to identify which group it belongs to.

Group 1 or spring-flowering clematis bloom in April and May from buds produced during the last growing season. Prune these plants immediately after blooming, but no later than the end of July in order to give the plant enough time to produce new buds for next year. Start by removing shoots that have bloomed; the only other pruning you will have to do is to remove any weak or damaged stems, or to control the size of the plant.

Group 2 clematis are the large-flowered hybrids which bloom in mid-June on stems from the previous season and often will bloom again in late summer on new growth. Remove dead or weak stems in late winter or early spring, leaving the best of last year’s buds. Once they finish blooming, deadhead all flowering stems or cut the plant back to 12 to 18 inches to force new growth for a second round of flowers.

Group 3 is made up of the late-flowering clematis, whose flowers are produced on the current season’s growth (these are the easiest to prune). In early spring, cut the plant back to 24 to 36 inches. Once the young shoots have grown to about 12 inches, prune half of them back to encourage more new shoots that will bear their flowers later than the first.

I have heard different opinions on how to treat iris foliage. Some say to cut it down after flowering, and others say to leave it. Which is correct?

Unlike most spring bulbs, bearded iris don’t require a period of cold to produce blossoms. They are also extremely drought tolerant – good for areas with little or no summer rains. Bearded irises are not actually bulbs, but rhizomes – a kind of thick brown root. The rhizomes need plenty of sun to bloom well and regularly. They do best in well-drained soil. To plant a rhizome, dig a large hole, fill the center with a mound of soil and set it on top. If planting in the fall when dormant, cut back existing roots to about three inches. Iris planted in the spring should have their roots fanned out around the sides of the mound. The rhizome itself should sit at about ground level. Growers differ as to whether it is best to cover the rhizome completely with a light layer of soil or to leave the tops a bit exposed.

Irises multiply out from the center, which gradually becomes dry and dead. Every three to four years, they need to be dug up, divided into new plants and replanted to provide the most flowers. Cut off dead blossoms and dead bloom stalks when the iris has stopped flowering, but don’t cut back the leaves until they begin to turn brown in the fall. The leaves are needed to produce next year’s blooms.

A common problem is the iris borer, one of the most destructive insect iris pests. Females lay their eggs on old iris leaves and other plant material in the fall. These eggs spend the winter on leaves and hatch in April or May. Cutting iris leaves back to a four-inch fan and removing other garden refuse during the fall can save iris plants from serious damage next season. Feed your irises a teaspoon of bone meal every fall and when you replant. You can feed again a month before they bloom if you like, but they are quite tolerant of just one feeding.

When can I plant cannas and dahlias out in the garden?

Since neither cannas nor dahlias are the least bit cold-hardy, planting outdoors for both of these beauties should be postponed until all danger of frost has passed. In order to get a head start on the growing season, you could start the canna’s rhizomes and the dahlia’s tuberous roots in containers that have a growing medium of one part potting soil, one part peat moss, and one part builder’s or horticultural sand. When it is safe to start planting your annuals (in southeastern Michigan that should be right around mid-May), then it will be safe to put your cannas and dahlias in the ground.