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 People have grown plants in containers since ancient times and whether gardening on a patio, balcony, deck or rooftop, the possibilities today are almost endless. The selection of containers has never been greater no matter what the function or budget. The explosion in the popularity of gardening has produced a huge variety of plants to choose from, including many designed specifically for container growing because of the rapidity with which plants dry out in containers. Humber Nurseries Ltd. does not offer any guarantee in such situations. However, many people have great success with container growing and we urge you to follow these tips and experiment. The rewards are well worth it.
As a general rule, try to select plants, which are at least one climate zone hardier than the one in which you live. For Toronto (zone 6), for example, choose plants, which are hardy to zone 5 or lower. This will increase your chances of success.
TYPES OF CONTAINERS
When selecting containers consider weight (when planted), portability, durability, size, colour and design. Colour may be less important particularly if trailing plants are used to cover the outsides and create a more natural appearance. For this reason, widely available plastic pails make ideal and economical containers. Remember that weight and portability are important if the plants need to be moved aside for parties or for protection from adverse weather conditions. Containers may be constructed from wood, plastic, Styrofoam, wicker, wire, metal, clay or concrete. Remember, clay pots chip and break easily. They will also crack if the soil is not removed and the planter turned upside down for the winter. A relatively new concept is the ‘grow bag’ or ‘wall bag’ which are simply strong plastic bags filled with planting mix and fertilizer. Self-watering containers are also available or may be easily constructed and are valuable because of the additional moisture requirements of plants above ground.
Generally, the larger the container the better, particularly for plants which ‘over-winter’ outdoors. Minimum depth should be 30 cm (12”) and width ideally should be larger than depth. Window or balcony boxes are usually smaller but should still be at least 20 cm (8”) deep and 25 cm (10”) or more wide.
Adequate drainage is vital to the health of plants and most containers already have drainage holes. If not, consider drilling holes yourself or include a 2-3 cm layer of broken clay or gravel in the bottom of the container (together with a small amount of charcoal to prevent the soil from turning sour).
 PLANTING MIXES
The best alternatives are the ready-to-use packaged soil mixes such as ‘Humber 3-in-1 Mix”, or the professionally formulated and lightweight ‘Premier Pro-Mix’. We strongly recommend using ‘Premier Hanging Basket and Planter Mix’ which is lightweight and has the advantage of moisture-retentive crystals.
Soil in containers should be replenished on a regular basis. We suggest removing one-third of the previous year’s soil, replacing it with fresh mix and mixing the old and new thoroughly.
FERTILIZER
Container plants require supplementary feeding for healthy growth. Water soluble or liquid fertilizers are ideal for container gardens and easier and more effective than granular types. Provide adequate nutrition for your plants through regular and frequent feeding. Avoid fertilizing dry or wilted plants; water thoroughly to improve their condition, and then fertilize. Be careful not to mix more than the recommended amount of fertilizer with water. Best results are obtained by simply following the manufacturer’s instructions on the package.
WATERING AND MAINTENANCE
Water is the most critical requirement of plants in containers. Remember that drying out can occur very quickly in the heat of the summer sun and moisture must be replaced as required. Strive to keep the soil in your containers moderately moist (not wet) and consider the use of mulch to conserve precious moisture.
VEGETABLES, HERBS AND FRUITS
Fruits and vegetables can readily be grown in containers throughout the summer growing season and many herbs easily grow indoors all year. Do not use soils containing moisture-retentive crystals for fruits, vegetables or other edible plants.
Tomatoes are popular and easy to grow. Varieties, which are particularly suitable, include balcony tomato, cherry tomato, and dwarf varieties such as ‘Tiny Tim’, ‘Sweet 100’ or ‘Sweet Million’.
Other salad ingredients such as lettuce, radish, onion, cucumber, pepper and carrot are also easily grown in containers. Beets, beans and peas are also often grown in balcony gardens. In fact, you can be successful with almost any vegetable listed in seed catalogues.
Herbs such as anise, borage, chives, dill, fennel, rosemary, sage, basil, sweet marjoram, summer savory and tarragon can all be grown in small containers.
Apples, the hardiest of fruit trees, can be grown in large containers. Dwarf trees are readily available, but ideal for restricted spaces are the new ‘Colonnade’ varieties with narrow columnar habits. ‘combination’ fruit trees (several varieties grafted on one tree) ensure cross-pollination and eliminate the need for more than one tree.
 Pears and plums are also quite hardy and present good possibilities where space permits. Remember that fruit trees require regular spraying programs to combat insects and diseases.
Strawberries are ideal for containers and require relatively little space. A wide variety of strawberry jars and planters exist primarily for this purpose. Consider ever-bearing varieties such as ‘Fort Laramie’ or ‘Tribute’, which produce fruit throughout the growing season.
Blueberries need very acidic well-drained soil and are ideal for container growing.
ROOF TOP GARDENS
Green roof design is the practice where the roof is the planter. This practice originated in Europe and has been used successfully in Toronto. An EPDM rubber liner is used on the roof, followed by a drainage tile, a layer of Styrofoam for insulation and soil-less mix. Visit www.greenroofs.ca and be sure to consult a structural engineer before starting any roof top garden project. A good reference book is Planting Green Roofs and Living Walls by Noel Kingsbury and Nigel Dumett.
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ANNUALS
The bad news is that most will have to be replanted every spring, but the good news is that annuals will guarantee you a continuous display of beautiful (and often fragrant) flowers from the time you plant them until frost arrives. Even this can be delayed since plants in containers can be moved or otherwise protected much more easily than in a typical garden.
There is a large selection of superb annuals for sun, shade or both in a wide range of colours suitable for containers: impatiens, begonia (fibrous and tuberous), petunia including cascading varieties, marigold, sweet alyssum, portulaca, lobelia, celosia, nicotiana, ageratum, scaveola, snapdragon, verbena, zinnia, nasturtium and of course geranium, including many scented and balcony or cascading varieties.
For fragrance consider sweet alyssum, nicotiana, geranium (especially scented varieties), heliotrope and evening scented stocks. This is just a partial list of colourful annuals and don’t feel restricted by it. Experiment with the ever-increasing selection of lesser-known varieties. Don’t forget pansies, which can be planted in very early spring and give you a great show of colour before the gardening season even starts.
Foliage plants such as coleus and ivies are excellent additions to container gardens and should also be considered.
Fall mums are still a traditional favourite for spectacular shows of colour in autumn.
Annual vines are ideal for creating privacy screens and provide a lot of colour in a limited space. They also help create a real gardening ambience by covering walls and barriers. Think about morning glory, moonflower, cup and saucer vine, scarlet runner beans, sweet pea and climbing nasturtium.
 PERENNIALS
The bad new is that herbaceous perennials do not bloom continuously the way annuals do, but the good news is that they do NOT have to be replanted every spring. In addition, such plants as ferns and hostas have outstanding redeeming qualities such as beautiful or handsome foliage. Perennials are relatively new to the container garden scene but there is already an extensive list of hardy candidates: Achillea, Campanula, Gypsophila, Aegopodium, Cerastium, Artemesia, Astilbe, Iris, Oriental Poppy, Delphinium, Coreopsis, Stonecrop (especially ‘Autumn Joy’), Hosta, Hardy Ferns, Veronica and Michaelmas Daisy. Again, this is only a partial list and feel free to extend it with other hardy herbaceous perennials.
PERENNIAL VINES
Very hardy vines can be readily grown in containers. Flowering varieties include Clematis and Climbing Honeysuckles. Excellent for screening and brilliant fall colour are the self-clinging (no need for a trellis) Virginia Creeper or Boston Ivy. Climbing Hydrangeas are recommended for sunny or shady locations.
ROSES
The rose still stands supreme above all other flowers and yes you can grow roses in containers and enjoy beautiful and often fragrant blooms all season long. Again your chances of success are best with hardier varieties and there are now more than ever to choose from including climbers. Our favourites include ‘Iceberg’, ‘Champlain’, ‘Morden Blush’, ‘Henry Hudson’, ‘Sea Foam’, and ‘Martin Frobisher’.
Favourite climbing roses suitable for container gardening include ‘John Davis’, ‘New Dawn’, ‘Blaze Improved’ and ‘Captain Samuel Holland’.
Tree roses are particularly stunning accent plants and are available in a wide variety of colours but require winter protection. Two varieties, which do not require winter protection, are ‘Hansa’ and ‘Therese Budget’.
WATER GARDENS
Water in a container, fountain or cascading feature adds life, movement and a new dimension to any garden. Using a half-barrel together with plastic barrel liner will give you a modest start to which you can add aquatic plants and fish. A wide selection of plants is available including hardy varieties, which require no winter protection, and tender or tropical varieties, which must be wintered indoors.
And what would a water garden be without fish? Minnows, goldfish and fabulously coloured Japanese Koi are all available to give your garden that extra splash. Humber Nurseries carries a complete line of ponds, filters, fountains, accessories and virtually everything required to make your water garden a rousing success.
Please see Pond Green Thumb Guides GT 106, 107, 311, 322, 338 for more information.
OTHER FEATURES
Think about pergolas, arbours, walls, rockery or decorative stone, lighting, garden furniture, ornaments and statues. These ‘finishing touches’ may be all that’s required to make you container garden a masterpiece.
TREES, SHRUBS & EVERGREENS
Hardier evergreens can also survive in containers but should have soil depth of at least 40 cm (16”) and diameter at least 30 cm (12”) greater than the diameter
of the root ball. Extra peat moss and humus are highly recommended additions to the soil mix. Choose from Juniper, Spruce, Pine and Cedar including the many dwarf forms. Dwarf Alberta Spruce, is a traditional favourite for container gardens and thrives in sun or shade, but requires winter protection (use burlap) if facing south or west. Evergreens require plenty of water and it is particularly important that they be thoroughly watered prior to freeze-up.
Trees and shrubs can be successfully grown in containers but be sure to use bigger containers for larger growing varieties. Hardier trees include Birch, Lilac, Crabapple, Serviceberry, Aspen and Willow among others. The list of shrubs to choose from includes Caragana, Potentilla, Sandcherry, Sumac, Dogwood, Amur Maple, Ninebark,
Burning Bush, Forsythia, Honeysuckle, Lilac, Viburnum, Spirea and others.
FINAL THOUGHT
Please remember, all of these are guidelines and should not limit you in exploring various possibilities in container gardening. Why not let your imagination run wild and see where it takes you? Many good books exist in which the authors provide valuable tips and information. Some experimenting may be necessary to find what works for you in your specific location and under your conditions.
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