How to keep your outdoor plants healthy and strong

Once you've picked plants for your property, you'll want to keep them happy and healthy. Here's how:

• Most herbaceous perennials, such as aster, daylily and phlox, need regular division.
• That means digging them up every three to five years, literally dividing the roots into smaller clumps by cutting or by shaking them apart and replanting them.
• Division promotes profuse flowering and new, vigorous growth.
• Astilbes are a case in point: If left undivided, they tend to flower less and less over the years, as their roots get crowded and woody.
• The same clump, once divided, can explode with blossoms. But don't automatically divide everything. Some perennials simply don't need division, and a few downright detest it.
• Check a good reference book before dividing any perennial whose preferences you don't know.

• If you plant trees or perennials so close together that they shade one another as they grow, eventually one of them will have to make way for the other.
• Although it's hard to imagine a tiny seedling as a full-fledged plant, determine plant spacing according to the plant's mature size, not its size when you get it.
• This is even more critical for trees than for perennials, since they are tougher to move once established. Any good plant reference book will tell you a plant's size at maturity.

• Hardy plants are happy to go dormant and spend the winter outside, but some garden favourites, such as dahlias, cannas and gladioli, aren't tough enough to survive very cold winters.
• If you grow them outside their range, remember to dig them up in fall just when frost cuts down their leaves.
• If you forget to, plants that could have given you pleasure year after year will turn to mush when they freeze.
• These tender bulbs and tubers all have different needs for winter storage, so do an online search, consult a book or check with your local garden centre for more specific instructions.

• Spring bulbs are a joy — it's undeniable. That burst of colour when most other plants are still dormant is just the remedy for the winter blahs.
• But if your perennial garden is new, wait a season or two before planting bulbs.
• You want to make sure you're happy with the overall layout and won't be making big changes, because if you decide to move things around midseason, you may find yourself spearing bunches of brand-new bulbs with your spading fork.
• Rather than have to replace them, be patient and put bulbs in when you know everything else will stay put.

• What makes a groundcover beautiful is the visual mass of a large planting and its clear separation from the surrounding area.
• If you maintain a sharp boundary, you'll also increase the life of the planting by preventing grass or other plants from invading your groundcover.
• Create a line of demarcation with hardscaping products, such as brick or metal-strip edging, or by using a spade to cut a clean edge twice a season.

• People who design landscapes for a living say that planting two different groundcovers together or in adjacent areas is like trying to wear two outfits simultaneously. It just doesn't work.
• Groundcovers are supposed to spread, so eventually two different ones in the same area will grow together, look like a mess, and have to be torn out.
• Let each groundcover shine in its own dedicated space.