Gardening in Containers

There are, of course, many other reasons why the popularity of this form of gardening is growing. Garden centres now offer a much bigger range of attractive tubs, pots, troughs, hanging baskets, vertical garden kits and window boxes and an even greater variety of plants to grow in them.

Moreover, there are new, efficient potting mixtures these days which greatly reduce the chances of failure, and plant breeders have developed plants more suitable for tub culture. However, the two outstanding advantages of gardening in containers are that they are portable and that almost any plant can be grown in them – flowering annuals, bulbs, ferns, creepers, herbs, shrubs and trees. There are even specially bred compact forms of fruiting plants for confined space

To be a successful container gardener you must choose the right plant for your situation. Balconies are often windy, so anything you plant should be able to stand up to the breezes. The amount of sunlight is very important and will also influence your choice of plants. Sun-loving plants – which includes vegetables – need at least four to five hours of sunlight each day to grow successfully, so check the amount of sunshine before spending money on plants that may not be suitable. Containers must have free drainage, otherwise your plants will drown. Most pots and tubs have one or several drainage holes 1–2 cm in diameter.

Ordinary garden soil is usually unsuitable for pot culture because it does not drain well and tends to set hard. Proprietary potting mixtures, which are available from garden stores and nurseries, are open, porous mixes which are very satisfactory and have the added advantage of being free from weed seeds, soil pests and plant diseases. Special potting mixes like orchid compost, African violet mix, cactus mix and bulb mix are available too.

For the best quality potting mixtures look for those that meet the Australian Standard, usually shown as a ‘five ticks’ logo. This guarantees that the potting mix has been produced to the highest possible quality. Cheap potting mixtures are just that: cheap. They are rarely a bargain. When potting up most plants, don’t be tempted to put a small plant into a large pot with the idea of saving yourself some work. Plants do not thrive in over-large containers – some even prefer to be crowded. It is best to move a plant into a slightly larger pot when the previous one fills with roots.

Whatever you decide to grow in your pots, remember that container-grown plants have a restricted root system and cannot forage for moisture as they would do in the open garden. On hot summer days, daily watering may be needed – perhaps twice a day if the plants are in full sunlight. Always water thoroughly – not just a sprinkle. Use a water-breaker or a watering wand rather than a hose nozzle. A water-breaker delivers a large volume of water gently onto the potting mix and causes minimum disturbance. When potting, leave a margin between the soil level and the rim of the container. When watering, fill this space slowly with water until it weeps out of the drainage holes. A mulch of grass clippings, compost, coarse gravel, pebbles or pine bark helps to reduce evaporation and cools the surface soil. Good drainage and frequent watering also means loss of plant nutrients. Regular, small amounts of fertiliser are needed to keep plants growing strongly.

Always apply fertilisers to moist soil to avoid burning young roots. The water-soluble fertilisers, such as Thrive or Aquasol, are suitable for regular liquid feeds. Use at half-strength for tender plants. Slow acting and controlled-release fertilisers (such as Acticote) or organic pellets (such as Dynamic Lifter) are also suitable to provide nutrients over a long period. Whatever fertiliser you choose, always use it according to the manufacturer’s directions. Too much fertiliser for potted plants can be disastrous, especially if the mix becomes dry, and salty granular fertilisers are best avoided for potted plants.

Container-grown plants are not immune to attack by pests and diseases. Grubs, bugs, blights and mildews must always be guarded against. A few plants on a balcony can often be kept clear of caterpillars, snails and other leaf-eating pests by picking them off by hand or spraying with low-toxic insect sprays which are suitable for controlling pests of potted and indoor plants. Pyrethrum-based sprays such as Bug Gun or insecticidal soaps such as Yates Nature’s Way Citrus & Ornamental Spray are ideal. A few pellets of snail bait at the base of potted plants will control snails and slugs.

• Camellias and azaleas with all-year-round foliage and exquisite flowers in season make excellent tub specimens. They do best in partial shade or filtered sunlight. They prefer acidic potting mix, so proprietary mixes that are marked as being suitable for azaleas and camellias are the best choice for growing these plants successfully. Growing these acid loving plants in tubs is a good solution if your garden soil is alkaline, which it may well be in some districts.
• Hydrangeas make magnificent tub plants for shady situations, although they do look rather bare in winter. They give a wonderful flower display in summer and can be brought indoors when flowering. Flower colour depends on whether the mix is acid or alkaline – blue in acid soil, pink in alkaline. If you want your hydrangeas to be a particular colour, grow them in a tub and treat the mix accordingly.  
• Fuchsias – and there are dozens of varieties – are dependable flowering shrubs for tubs, pots or hanging baskets in cool and temperate climates. Flowers in white, pink, red and purple are produced over a long period.
• Gardenias, with handsome glossy leaves and waxy, white, fragrant flowers, make good tub specimens. Gardenias prefer full sun or half sun in a warm, sheltered spot. In the right position (especially in warm climates) some varieties of gardenias will flower from spring to autumn.
• Daphne is another neat, evergreen shrub with exquisitely perfumed pink, red or mauve flowers in late winter and spring. Plants need good drainage and are often more reliable in a large pot or tub than in the open garden. They prefer morning sun but shade for the rest of the day.
• Geraniums will provide a bright patch of colour on a sunny terrace or patio. Grow them in tubs, large pots or window boxes; with plenty of sun they will flower from early spring to late autumn. The ivy-leaf trailing varieties are ideal for hanging baskets.
• Bougainvillea is another sun-lover, especially for warm, northern climates, and dwarf varieties are now readily available. These are best for containers and give a magnificent, long-lasting display of flower bracts.
• Citrus trees are both ornamental and useful tub plants for outdoor living areas. The smaller citrus trees like cumquats and limes are easy to grow in tubs, but potted lemons, oranges and mandarins may need pruning to keep them within bounds. Choose citrus grafted onto dwarfing rootstocks.
• Japanese bamboo (Nandina), with its lacy foliage, makes a good container plant and can be kept in bounds by pruning. True bamboo, which belongs to the grass family, gives an oriental effect for tub culture but only dwarf varieties up to 2–3 m tall should be chosen.

Roses do well in tubs and pots and they are easy to grow, though obviously the miniature varieties and small floribundas will perform best. They are not fussy about climate and can withstand hot summers as well as freezing winters – provided you don’t let the container dry out. Full-sized roses need a pot at least 50 cm or more in diameter to allow room for the roots to develop properly. Fertilise with controlled-release fertiliser in early spring, as new growth begins, and again in early autumn.

Your display will last longer if you keep removing dead flower heads to encourage the formation of new buds. Never allow rose hips (fruits) to develop because they drain energy from the plant and inhibit the growth of more flowers. Here is a list of some roses suitable for container growing – and remember that roses generally look better massed than as single specimens. Try to group several pots together.

• Floribunda types: ‘Apricot Nectar’, ‘Confetti’, ‘Friesia’, ‘Iceberg’, ‘LovePotion’, ‘Marlena’, ‘Red Gold’, ‘Regensberg’, ‘Saratoga’ and ‘Sonoma’.
• Miniatures: ‘Amorette’, ‘Chameleon’, ‘Foxy Lady’, ‘Green Ice’, ‘Holy Toledo’, ‘Hopscotch’, ‘Guletta’, ‘Kaikoura’, ‘Ko’s Yellow’, ‘Lavender Lace’, ‘Little Red Devil’, ‘Magic Carrousel’, ‘Mary Marshall’, ‘Ocarina’, ‘Otago’, ‘Over the Rainbow’, ‘Petite Folie’, ‘Royal Salute’, ‘Snow Carpet’, ‘Starina’, ‘Sunspray’, ‘Wanaka’.

This information is from the Yates Garden Guide: fully revised & updated 44th edition, HarperCollins, $39.99. You can have this information and so much more at your fingertips by purchasing the Yates Garden Guide, available at all leading bookstores and Bunnings stores.