Tubs and containers can be attractive in themselves but with the right plants, they can be real garden features. Plumbers use old toilet cisterns, mechanics make plant in tyres and housewives frequently use old tins, jars and bottles from the kitchen. All sorts of things can be used as a container to grow plants in and in this day and age, the range of pots, tubs, hanging baskets and planter boxes available in our nurseries seem to be never ending. So the search goes on for something unique and appealing which will set your garden apart from those of your friends and neighbours.
Why Grow in Containers
People grow plants in containers for a whole range of reasons, but the following are the most common:
Containers can be moved but a plant in the ground cannot. When the weather is too hot, dry, cold or windy, it can be moved away from these extremes. When a plant is in flower it can be moved to where you can see it. When it is unattractive, it can be moved away. “Outdoor plants” can even be used indoors for short periods if you want to “dress up” the inside of the house when entertaining.
If your soil is poor, it may be easier to grow plants in pots than to try to improve a very bad soil. Soils can take a long time to build up, often years, and in the interim, plants in a quality potting soil might give faster, healthier and more attractive growth than is possible in the soil.
Container plants can be set at any level such as on a table, bench, or as a hanging basket. Good quality, lightweight potting mixes are easier to plant in and easier to weed. For the elderly or physically handicapped, container gardening is often possible where garden beds are just too difficult to use.
Drainage is sometimes just not good enough to allow us to grow our favourite plants. Containers generally drain better than soil because they are raised above soil level. As such, container gardening is particularly suited to plants which demand perfect drainage, or in areas where too much water can be a problem.
Containers in themselves can be a feature. Decorative containers add a character to a garden and this can vary depending on what material the container is made from; its colour, how it is shaped and of course the plants chosen to grow in it. The natural tones of wood and terracotta suit natural gardens, while the polished and colourful surface characteristics of plastics and glazed ceramics suit more formal or modern garden styles.
To Control Plant Size
Plant growth is restricted and consequently slower in a container. A Christmas tree might last for many years in a pot, but grow to a large tree, very quickly in the ground. The same principal is used with bonsai.
To Reduce the Competition
In the ground, plants need to compete for water and nutrition. Usually the more vigorous plants thrive and the weaker, but sometimes prettier plants suffer. In containers, each plant has its own soil and doesn’t need to compete with others.
PROBLEMS WITH CONTAINERS
Plants grown in containers often develop problems, but if you look out for and overcome these, you are well on the way to success with container growing.
For example, when pots continually fall over, it is often a result of either wind, being too top heavy or simply being knocked. If wind is the problem, a simple solution is to move the pot to another position. If the pot is top heavy, sit it inside a planter box. And, if it is being knocked all the time, try a heavier potting mix or use a larger, heavier pot.
Soil drying out is a common problem with pot plants. When wind or sun is the cause, move the pot to a sheltered position. If the plant is pot-bound however, you need to re-pot it, remembering to trim some roots and foliage at the same time. Of course the plant could be too well-drained in which case you should paint the side of unglazed pots or unsealed timber tubs. Mulching the surface with sphagnum moss or pine bark is a good idea.
Where poor drainage is the problem, possible solutions are to move the pot to an airy or drier part of the garden, provide more drainage holes, use better draining potting mix or even sit the pot on top of bricks or pavers.
Nutrient deficiencies are usually the result of poor potting soil (you should pot up), the soil being too wet or too dry (regulate your watering), the wrong pH (use a pH test kit and adjust the pH if found to be wrong).
When algae, moss or liverworts grow on the soil surface, it is often a result of the plant receiving too much light, water or nutrients or a combination of these factors.
HOW TO MAINTAIN PLANTS IN POTS
Re-pot container plants regularly. Fast growing plants need re-potting at least annually. Slow growing plants need re-potting every three years. If you want to keep a plant at the same size, remove 10-30% of the roots and old soil, and the same amount of foliage when you re-pot. If you want a plant to grow bigger, re-pot it up into the next size pot.
If you are uncertain as to whether there are sufficient drainage holes, cut some more. Holes can be cut in plastic with a knife or secateurs. Wood or ceramic pots can be drilled.
Plants such as palms, bulbs or numerous indoor plants are susceptible to root rots and will benefit from large stones, charcoal chunks or broken terracotta pot fragments placed as a layer at the bottom of the pot, under the potting mix.
Use a potting mix which has an even texture. Avoid large lumps of soil or organic material. If one side of the pot has larger chunks of organic material, then it is likely to hold more water than the other side. Price and brand names do not guarantee a quality potting mix. Compare mixes and use those which have an even, consistent texture. What you see at the top of the bag should be the same as what you see at the bottom.
Containers drain more freely than a garden bed, consequently nutrients tend to be washed through and lost. As such, regular feeding of container plants is critical. Either use a slow release fertilizer like Osmocote or Dynamic Lifter which releases nutrients slowly into the soil or use smaller quantities of faster acting fertilizers such as Maxicrop, Nitrosol or Seasol more often.
Add Zeolite to potting mixes. This helps the mix retain nutrients, counteracting the leaching caused by continual watering. It is available in nurseries.
Pots must be watered regularly since they will dry out faster than garden shrubs. Watering must be done when needed, not according to time periods! It is a big mistake to water once a day or once a week – the timing will vary throughout the year.
Pots which are in full sunlight or standing on pavers or concrete should be watered more often. Also, plants with a large amount of foliage in proportion to the pot size need more frequent watering.
Pot plants kept in air-conditioned or heated buildings need more frequent watering, as do plants which are growing fast.
Hanging baskets in well-ventilated places have a high water requirement, while containers kept closer to the ground, or away from wind and heat use less water.
Often, if a container plant becomes too dry, it is hard to get it wet again. If water rolls off the surface and down the sides of the pot without soaking in, it may need some special treatment. Fill the laundry tub or a bucket with water and sit the pot immersed for five minutes. Once wet, treat with a Soil Wetter (from a garden centre). This will lessen the chance of this problem recurring.
If you want to make watering pot plants easier, a drip irrigation system can be installed with individual drippers to each pot. The only problem is that if an outlet becomes blocked, one pot might be missing its watering for a while before you notice. If drippers are checked every week or two, there should not be a problem.
Ventilation and Light
Plants need fresh air and light around them. Pot plants which are too close together can suffer with growth becoming lopsided and general health deteriorating.
Pot plants put indoors frequently suffer from a lack of light. Unless they are a shade-loving plant, keep your indoor plants near a window. Air-conditioning, gas stoves and gas heaters can also affect indoor plants. If the weather outside is good, the plant will do best in a room with open windows.
Plant roots heat up faster in a container than in the ground. Potting soils which contain plenty or organic material such as bark or peat moss, are less of a problem but can still suffer from overheating.
In very hot weather, containers sitting on concrete or any other hot surface must be watched carefully.
In hot conditions, heat is reflected off surfaces such as brick walls, metal sheds and concrete. This reflected heat can burn foliage and heat the pots. In extreme situations, the container might need to be moved.
Water hot surfaces around pots and keeping the soil moist will help beat hot days, but be aware that the combination of water and hot sun on the foliage will burn many types of plants.
TYPES OF POTS
Deeper pots have less air spaces between the soil particles since the weight of the soil on top squashes the soil underneath. Deeper pots therefore need a more open soil mix.
Wider containers are more stable (less likely to tip over).
A pot needs to have a sufficient number of large drainage holes to allow water to drain quickly away from the bottom.
Roots tend to coil more in a round pot than a square pot. Root coiling at the bottom of a pot is reduced if the base is more tapered.
Roots tend to grow through the bottom of pots when there is moist soil, compost or mulch under the pot. It’s therefore better to stand pots on top of a dry paved surface.
Sprinkling a layer of coarse sand over the pot surface will reduce weed problems and control the growth of moss.
Plastic pots are clean, don’t dry out as fast as terracotta or wood, are lightweight and are available in a great variety of colours. Some types of plastic deteriorate in U.V. sunlight and crack after a couple of years, so don’t expect too much from the cheaper varieties.
Fibreglass is clean, durable and lasts much longer than plastic, but it will eventually discolour.
Unglazed pottery absorbs water from the potting mix. For this reason, plants in terracotta need to be watered more often in hot weather, perhaps twice daily. Plants which prefer a drier or well-drained soil, will often prefer a terracotta pot. If the pots are too wet, they can show unsightly white salt marks or grow green algae on the sides. Glazing puts an impermeable layer over an otherwise water permeable pot. This reduces the rate at which they dry out and can lead to drainage problems if there are inadequate holes in the bottom. Pottery is heavier to move and more likely to break than other materials, but it is also very often the most attractive.
Wooden tubs and pots look good and create a very different effect to other pots. However, if untreated they can rot after a year or two. Wood is often painted on the inside with bituminous paint to waterproof it; and painted on the outside with a timber preservative. Creosote treatment can also be used, but this adversely affects some plants.
WHERE TO PLACE POTS
Pots are always easier to maintain if they are kept together in the one part of the garden, but that doesn’t necessarily make the best aesthetic use of your container plants.
Two large tubs are ideal either side of an entrance. At the beginning of a path, they make a visual statement, telling people this is where the path begins! They have a similar effect at the top and/or bottom of stairs, either side of a doorway or either side of a garden arch.
Hanging baskets or tubs can be used beside a bare wall to soften the harshness of brick or metal. Baskets can be used to give height in a new garden where most plants are still below eye level.
A veranda or patio can be made more attractive with container plants, without needing to dig up the paving or timber decking.
If you have a bad back, try putting your pots on a raised bench to save bending. A simple bench can be made by placing a railway sleeper between or on top of two stacks of bricks.
If you bring pots indoors, carefully consider where you put them. Plants need time to adjust to new environments. They shouldn’t be taken from cold to hot or sunny to dark places overnight.
PLANTS FOR POTS
Virtually anything can be grown as a container plant, however due to the unique problems associated with container growing such as pots tipping over, soil drying out, nutrient deficiencies and so on, it is easier to grow plants in pots which can withstand these sorts of problems.
Cacti and succulents withstand dry periods and many Australian natives and other plants from semi-arid climates will also withstand dryness.
Low-growing shrubs and creeping plants are less likely to become top heavy, while plants which can be pruned regularly and hard, can be kept from becoming top heavy.
Plants with more open foliage are less likely to blow over than those with very dense foliage.
Container plants also need to look good. You need to consider the balance between the aesthetics of the pot and the plant If the plant looks spectacular, it will take away from the pot. If the pot is very colourful and the plant is not, people will only see the pot.
Hanging baskets need creeping or spreading plants which hang down.
Tall plants are more stable if the container has a wider base.
Formal plant shapes suit formal pots. A formal topiary is best in a perfectly shaped tub such as a glazed ceramic, perfectly round container, or painted square timber planter box. Informal plants go with informal pots. A sprawling native bush is best in a pot with natural and perhaps uneven colour and texture such as a timber tub or rough terracotta pot.
Match the colour of the plant and container. Consider colour changes which will occur with weathering of the pot and seasonal changes which will occur with the plant.
Flowers in Pots
Bulbs and many annual flowers grow well in pots, if for no other reason than the fact that drainage can be better managed. Petunias, marigolds, alyssum, lobelia, primulas and so on are all good candidates for a 3-6 month stint in a pot or tub. Bulbs such as daffodils, hyacinth, crocus, hippeastrum and lily of the valley are also suitable subjects.
Container Plants for Cold Climates
Azalea, Acer palmatum, Buxus (Box), Chamaecyparis, Cupressus, Juniperus, Leptospermum scoparium, Epacris longifolia, Correa reflexa, Lonicera nitida
Container Plants for Mild Climates
Asparagus fern, Aspidestra, Begonia, Bromeliads, Brachycome multifida, Azalea, Camelia, Cordyline, Fuchsia, Geranium or Pelargonium, Palms, Cymbidium and Dendrobium, Orchids, Strelitzia, Melaleuca incana, Lonicera nitida, Nandina domestica.
Container Plants for Hot, Dry Climates
Agave, Cacti, Cordyline, Brachycome iberidifolia, Helichrysum bracteatum, Clianthus formosus (Sturt Desert Pea), Philodendron selloum.
Container Plants for Hot, Wet Climates
Black bamboo, Bromeliads, Bougainvillea, Palms, Orchids, Strelitzia, Lonicera nitida, Philodendron selloum, Spathiphyllum “Clevelandii”, Nandina domestica, Gardenia jasminoides.
Best Fruits for Containers
Citrus, Pepino, Peach and Nectarine (dwarf varieties), Pomegranate (dwarf type), Strawberry.
Best Vegetables for Containers
Capsicum, Eggplant, Lettuce, Tomato, Zucchini.