Perennial Plant Care

Perennial flowers are the way to go! They return year after year, bringing colour to the garden. Once established, they require little maintenance. Here are perennial plant care tips—from planting to dividing to winter care.

WHAT ARE PERENNIALS VERSUS ANNUALS

Perennials are plants that live in the ground for more than two years while annuals only grow for one season, produce seeds, and then die. There are also biennials which live for two growing seasons before setting seed. Perennials die back down to the ground every autumn, but their roots survive the winter, and plants re-sprout in the spring.

• Examples of perennials: black-eyed susans, purple coneflower, sedum, peony, beared iris, daylily, salvia, coreopsis, hosta, phlox, rubeckia, dahlias, aster, Russian sage, and crocosmia.
• Examples of annuals: zinnia, petunia, impatiens, marigold and sunflower.

Specifically, when we refer to perennials, we mean “herbaceous perennials,” not trees or shrubs. 

Once established, many perennials need minimal upkeep in the form of watering and fertilizing, since their roots are more far-ranging than annual plants’ roots.

Many perennials spread readily, filling out garden spaces, and providing more and more colour each year.

WHEN TO PLANT PERENNIALS

Perennial flowers, unlike annual flowers, are best planted in the spring or the autumn, but can be planted in summer too. When selecting perennials, be sure to consider your planting zone and whether your garden is shady or sunny. Also think about when the perennials bloom so that you can select plants that keep the colour blooming throughout the growing season. 

HOW TO PLANT PERENNIALS

When you buy perennial plants, it’s really the roots that you’re planting; this is what allows the plants to return year after year.

Container-grown perennials (a small plant already rooted in soil and growing): Dig a hole that’s a little wider (but no deeper) than the container. Add a handful of growmore fertiliser to the bottom of the hole. Gently loosen the roots before removing from soil. Backfill hole with soil and press around plant until firm. Water well.

Group together plants that have similar water requirements.

PERENNIAL PLANT CARE

• Water deeply, especially during the first growing season. If planting in the autumn, water perennials regularly until frost. 
• The soil should never be overly dry or wet. Avoid getting water on the foliage to avoid disease. Fertilize with low-nitrogen, high-phosphorus fertilizer to encourage more blooms and less foliage. Most perennials do not need heavy fertilization. A single application in spring (after the soil has warmed) is usually sufficient.
• Mulch around plants to keep weeds to a minimum and retain moisture.

• Create a neat, clean edge between your lawn and flower bed. Use an edging tool or install permanent edging.
• Remove spent flowers (deadhead) to prevent plants from using their energy on seed production and to stimulate reblooming. Coreopsis, phlox, veronica, and delphiniumare rebloomers.
• Put plant supports in place early in the season, before plants get too big, so as not to disturb their roots. Put supports close to the plant and gently tie the stem to the support. For clump-forming plants—like peonies use a hoop. 

WHEN TO DIVIDE PERENNIALS

• To keep perennials performing beautifully, divide the biggest plants every 3 to 4 years when they are not in bloom.
• You’ll know when it’s past time to divide perennials because the plant produces fewer flowers or the centre of the plant looks sickly while the margins thrive.
• Spring and autumn are the best times for most perennials. In cold regions, we would recommend early spring so the plant has plenty of time to get established before the next cold winter. On the other hand, in hot climates, fall may be a better time to divide, giving plants the mild winter to get established.
• While most perennials need dividing, this is not only the case. Some exceptions include: peonies, false indigo (Baptisia), monkshood, bleeding heart, lupine, and poppy.

HOW TO DIVIDE PERENNIALS

Below is garden equipment that would be helpful.

• Shovel
• Garden forks
• Pruner
• Sharp knife

Choose a cool cloudy day, ideally before a rain.  This will be less stressful for the plant and increase odds of a good recovery. If the ground is dry, soak the soil around the plant.

Trim back the leaves or stems to 6 to 8 inches to make handling easier.

Just gently dig up the root ball, divide into smaller clumps, and replant for more perennials! Some perennials have root sections that just naturally separate and others are all tangled together so you’ll need to gently pry apart with garden forks. Prune away dead and damaged tissue, and make sure each section has a portion of roots and leaves.

Plant divisions as soon as possible, setting the plants at the same depth they were in the original bed. Water the new divisions well, and keep them well watered throughout their first year.

WINTER CARE OF PERENNIALS

• If your ground freezes, cover all your perennials with a protective mulch of compost or dry peat moss.
• Leave mulch on your perennial beds while the ground is frozen until you have several nights in a row with above-freezing temperatures. As you remove the mulch, add it to your compost pile.

For regions where temperatures can dip especially low, here’s a technique that allows the tougher perennials, such as alpines, to overwinter right in their pots:

• Many gardeners cover the pots with material such as microfoam (a ½-inch-thick white foam blanket with plastic backing on both sides) .
• Then scatter a thick layer (about 6 inches [15 cm]) of loose peat moss onto the blanket and put another layer of fabric on top.

Most containers don’t have enough soil volume to insulate perennial roots from freezing when winter temperatures drop. Two or three weeks prior to freeze-up, transplant into the garden any perennials growing in all but large containers.