Containers are pots or planter boxes with drainage holes in the bottom. They should be as large as possible and of as fine a quality as possible because every garden needs containers if only to fill in empty spaces in borders during the dog days of summer. However, used badly they just clutter up the joint and look awful. If in doubt, use one huge container as a focal point -- get a very modern metal or fibreglass one that will withstand freezing -- and change the planting with every season.

Containers should relate to the style of the garden, the house and each other. You can plant them with annuals that will provide instant bloom or with perennials that take a couple of years to show their stuff. You can design a whole garden with containers, of course, but experiment with them in clever ways so they add height, bulk or a jolt of surprise. For example, try setting a bunch of pots on a step ladder or plinth in a border to create a layered effect. No matter what you do, when designing with containers remember the following tips.

1. Use containers in transitional areas (porches, doorways, entry courtyards) to continue colours from house to garden.

2. Move large containers around while they are empty to get them in the right spot. Once filled, these things weigh a ton.

3. Make sure any container is raised off the ground on bricks or chocks to aid drainage and to keep them from freezing and cracking in winter.

4. Put poolside containers on casters so they can be easily moved out of the sun -- the heat reflection from the water can be brutal -- or out of the way at pool-party time.

5. To make a garden appear longer, place large containers in the foreground and set increasingly smaller ones behind.

6. Avoid using silly, little containers. Buy larger ones than you think you'll need; little pots doted about look haphazard and uncomfortable.

7. Match the pot to the plant's ultimate size. Don't place a small plant in a huge container or vice versa.

8. Never put big containers on pedestals. It is unsafe and unnecessary.

9. Make sure containers sit absolutely level. It is visually insulting to see containers listing sideways.

10. Use a gravel mulch in containers to hold in moisture and discourage squirrels.

Click here to discover Marjorie's 10 essential plants.

Marjorie Harris is the national gardening columnist for the Globe and Mail and the editor-at-large of Gardening Life magazine. She is the author of several gardening books, including The Canadian Gardener and Botanica North America. She lives in Toronto, where she gardens seriously and for the amusement of her husband, writer Jack Batten. To learn more go to Marjorie's website at www.marjorieharris.com.

Excerpted from How to Make a Garden: The 7 Essential Steps for the Canadian Gardener by Marjorie Harris. Copyright 2006 by Marjorie Harris. Excerpted with permission from Random House Canada. All rights reserved. No part of this excerpt may be reproduced except with permission in writing from the publisher.