by John Richmond
Once you have the structure of a garden - the paths, beds, borders, hard surfacing, trees and shrubs - then you need the furnishings. Decorative containers offer interesting ways to grow a wide variety of plants. In a container you can control the soil, vary the watering regime, adjust the amount of sun or shade, group plants for impact - and ungroup them if the idea doesn't work. With decorative containers you can make a sculptural statement in the garden. With plain containers you can build banks of colour and foliage that hide the outlines of the pots - or any other area you want hidden. Some gardens wouldn't even be possible without containers.
People have the urge to garden no matter how unpromising the site. I regularly walk past plots of land where there is little soil or space. A set of steps going down to a town basement? Put pots along the side of the steps. A balcony? Use pots brimming with plants to hide the edge. A concrete or paved courtyard? Disguise the walls with pot grown shrubs and climbers. A thin strip of road frontage? Colourful annuals in pots will make the approach more interesting. The possibilities are endless as long as some basic rules are followed.
Rule 1. It's your garden. Use any container you want or can find. Attractive glazed pottery is readily and fairly cheaply available. Last winter I bought a collection of three fairly large, blue glazed oriental pots for less than £12 (about $18 US) and used them for cannas and lilies this summer. Clay and terracotta pots look good anywhere. There is nothing to stop you from using whatever comes to hand. Plastic pots, half barrels, old water tanks, oil drums, large tin cans, old boots, polystyrene fish boxes - if they hold container soil you can adapt them. Just make sure the container is large enough to hold a good volume of soil (the bigger the better) and has a drainage hole or holes so that excess water can escape.
Rule 2. There few plants that cannot be grown in a suitable size container. This includes trees and shrubs, climbers, perennials, ferns and bulbs as well as the more commonly grown annuals and tender perennials. Don't limit yourself to a few common annuals. Experiment. If all you have is a shady spot then use containers full of shade lovers. Ferns, hostas, camellias, pieris, heucheras and many others can provide foliage interest, while flowering interest can come from fuchsias, lilies and impatiens. If your container garden is sunny but windswept use plants that thrive in these conditions. Hebes, cistus, cordyline, pittosporum and many others will all add decoration and provide a shelterbelt behind which more delicate plants can grow. If you need height try climbers. Small flowered clematis, morning glory, the less vigorous climbing roses, nasturtiums and many others grow well in containers. If your container area is really warm and sheltered then try tender plants. Sub-tropical plants like bougainvillea, brugmannsia, oleander, tibouchina and hibiscus will thrive outside in warm summer areas - although they will need winter protection in all but the most favoured sites.
Rule 3. Once you decide to grow plants in containers you must never neglect them. Their roots can't escape and seek food or moisture, and the top growth can't travel long distances to seek light. This means that you must give them the right conditions in the first place and continue to provide these throughout the life of the pot.
Let's start with container soil. Good container soil should be free draining but also hold moisture. It should also suit the pH requirements of the plants. Rhododendrons, most heathers, camellias, pieris, skimmia, citrus and many others must have acid soil. You can buy this at the local garden centre. Others benefit from acid soils. Hydrangeas will never be blue unless the soil pH is below 6. They will grow happily in more alkaline conditions but will only come pink or red.
I use a variety of container soils depending on the requirements of my plants. For most I use a 50:50 mix of soil based and organic potting soil. The soil provides weight, a reservoir of trace minerals, and an environment in which beneficial soil organisms flourish. The organic component provides water-holding materials and also improves the drainage. For acid requiring plants I use a similar mix in acid container soils. For plants that need free drainage I add very coarse sand or fine gravel. To all of these I add drainage material - broken clay pots, stones or coarse gravel, or polystyrene chunks in the bottom of the pot, and a mulch of gravel on the top. What all of this means is that the plants never sit in water, but have water constantly available unless the pot dries out. If it does the soil part makes re-wetting far easier.
If all you grow is annuals or tender perennials started afresh each year you can completely renew the container soil each spring. Don't throw the old soil out. It makes good mulch for the garden. For more permanent plants renew the top 2 inches / 5cm of the soil with fresh material as growth starts in spring. Scrape off the gravel mulch and replace the soil with fresh mixture.
Regular feeding is a must. I now use slow release fertiliser added to the container soil when planting. This feeds the plants for a season but there is nothing to stop you using any soluble organic fertiliser and adding to the water once or twice a fortnight. Don't forget, the acid loving plants will need their own type of fertiliser.
Which brings me to watering. Never underestimate how much water most container plants need. A large container - 18in / 45 cm diameter or above - will need at least a gallon / 4.5 litres of water per session. In hot weather this can be twice a day. A gravel mulch helps to conserve moisture, and grouping the pots reduces evaporation, but container plants get through a lot of water. If this is a problem investing in an automatic watering system which will keep the plants constantly moist. Alternatively, grow plants that will stand some drought. I have a lovely pot of Aloe aristata, a succulent just about hardy with me. It will take days without water. Agaves, pelargoniums, yuccas, sedum, sempervivum, cacti - if they can survive your winters or you have a light frost-free place to overwinter them - all are suitable.
John Richmond is a keen gardener who lives and works in the South West of England. He has a scientific background as a professional ecologist. He has written occasional articles for gardening and other magazines in Britain since 1984, specializing in garden wildlife issues and hardy plants.