How to Prune Perennials

Question from Carla:
I have several perennials in my very small garden and I am not sure when or if I should cut them back. I live in Southern California. Some of my plants are Mexican heather, calibrachoa, and Marguerite daisy.

Answer from Pat:
People often ask landscape designers to design an easy-care garden full of perennials. It’s an oxymoron. Perennials aren’t easy, they are complicated, and many plants called perennial don’t live forever. Also, it’s often impossible to teach hired gardeners how to care for them since each one requires different care. It would help you a great deal to purchase a copy of my book and read the perennial section under “Flower Gardening” in every chapter as we reach that part of the year. Each perennial requires different soil, care, light, timing, and pruning. That said, this month, November is the time to cut back the entire perennial garden. Most perennials can take that treatment now. Some need to wait until spring or until 8 inches of new foliage called basal foliage emerges from the ground, usually in late winter. Then cut to that. Read my book to learn all these things.

Mexican heather (Cuphea hyssopifolia) is able to withstand drought if necessary but looks best with regular watering and what I call progressive pruning (in this case just a little clipping back year-round to keep it compact and stop it from spreading out and of course removing any dead when you see it. Do this right away to stop it from spreading. A good rule to follow is with plants that bloom year round, you can prune year round and feed throughout the growing season. Since it sounds as if you have not done any pruning, take any dead growth out now. Clip out a few inside branches here and there to let light into the center of the plant. Clean up the plant, clip back any wayward branches and shear in lightly into a rounded shape. After this just pinch branches back year round. Don’t let it spread way out. Mexican heather never gets very tall but it can spread. It’s easy to keep it at a foot tall, which is what you want. After pruning fertilize lightly with organics and renew mulch. It is best to fertilize lightly during the growing season. It’s a little late now but if the plant is starved fertilizer won’t hurt after pruning.

Million bells (Calibrachoa) is a short-lived perennial that needs good drainage and blooms just about year round. It needs little pruning since it tends to keep growing and blooming, popping a flower on each tip constantly during its short lifetime of one to three years. However cut anything dead out year round. Pinch back wayward branches as they appear. A little pinching back around the edges is usually all this plant needs year round. Many people grow it for one season only and then go out and buy another in spring but in a warm sunny spot this plant may keep right on blooming year round. If so pinch it back year round. Water after the soil dries out somewhat. If your plant has spread way out and looks messy and floppy now, you may be able to renew it this way: Just shear it all over lightly in November, removing all the flowers and a little tip growth and shaping the plant like a fat rounded cushion. Follow up with a little light organic fertilizer, cover the ground under the plant with a fresh layer of mulch, water and it should bounce back and start blooming again in a couple of weeks.

Marguerite daisies bloom mainly in spring. The correct pruning method for this plant is given in detail in the June chapter of my book. In June shear the plants all over taking off all the flowers and about 2 or 3 inches of the tip foliage. Follow up with fertilizer and water. If you didn’t do this in June, shear the plant lightly now and cut out any dead. Don’t ever cut it back into hard wood or it will die. Marguerites are short-lived flowering shrubs. They are not perennials. New ones are a little easier and more rugged than the old types and not so likely to die if pruned too hard, but please especially read up on this plant in Pat Welsh’s Southern California Organic Gardening on pages 243 and 244 and from now on with this plant follow this rule “With plants that have one main bloom season, prune after bloom!” . The other rule to remember is “With plants that bloom year round, prune year round.” There are exceptions to these rules but nine times out of ten these rules work.