11 Tips for Container Gardening
Containers open up a whole world of possibilities to the gardener. Owners of small gardens — including rooftop gardens — can plant up pots that can be moved around as required to decorate every surface, including walls and steps.
You can grow almost anything in containers, from edible plants to water-loving ones. You can even grow trees, but obviously, they will never reach the size they would in an unrestricted situation, simply because you would not be able to provide a container large enough for the full root span. Choosing slow-growing trees and shrubs will mean less work, and likewise, selecting drought-tolerant plants will cut down on the chore of summer watering in warmer areas.
The Right Pot
Make sure the potting mix (potting compost) that you choose is suitable for the plants you want to grow, and of course choose waterproof containers for any water plants.
Your choice of container depends on the style of your garden as well as what you intend to grow.
These colourful pots are cheap, durable and light to move around; some even look convincingly like terracotta. As they are waterproof, they don’t dry out as fast as porous containers, so the plants require less frequent watering and feeding. On the downside, they don’t always look very good in your yard, especially if you have a wide mix of colours and styles. If you’re using a lot of plastic pots, stick to one colour.
Wooden pots usually look attractive, especially in rustic or natural-style gardens. Like plastic, they are waterproof and generally look best if you stick with the one style throughout the garden. The disadvantages of wood include its weight and the fact that it will eventually rot, although that does take a long time to happen. You’ll need to raise them off the ground to minimise rotting on the bottom.
Ceramic pots include unglazed terracotta and glazed earthenware or stoneware. Terracotta pots, the traditional containers for plants, look good in most settings, while glazed pots are more decorative. Glazed pots and unglazed stoneware containers are waterproof, but terracotta pots are porous, so they can dry out fast and plants always require more frequent watering than waterproof pots. More frequent watering means more frequent feeding, as watering will wash nutrients out of the soil with every application. The disadvantages of ceramic pots include their fragility, weight and cost.
Concrete pots are heavy and best placed in their permanent position. Some are big enough to accommodate quite large trees, and when sold with a matching pedestal can make an impressive focal point in the garden. Weight and cost (especially the cost of the bigger, more decorative pots) are the main disadvantages of concrete.
A workable planting scheme for a container garden requires a lot of forethought. The pots themselves will play a major role in the final appearance of the garden, so pay attention to container shape, texture and colour to ensure your chosen pots complement the textures, forms and colours of the plants. If you can create interesting contrasts or subtle harmonies, it will beautifully unite the display.
Look for plants with exciting forms — deeply coloured, interesting foliage, for example — and match these to plain or patterned containers in good-quality materials. You can also paint or decorate your containers to provide interest, but try to keep the patterns clean and simple.
Containers are wonderful for changing the mood or defining the style of a specific area of your garden.
▸ You could use metallic pots to achieve a minimalist look, or traditional wooden trugs to convey a cottage-garden atmosphere.
Why not use one or two really large specimens in containers to create a stunning focal point? Try architectural plants, such as agaves and phormiums, or even a cactus or succulent if your climate is suitable.
▸ Use a simple flower or pot colour that coordinates with your garden furniture to enhance a seating area.
▸ Introduce some fragrant plants — such as fragrant nicotianas and lavenders and sweet scented-leaved pelargoniums — to an area of the garden where you like to relax.
▸ A display of the one type of plant, such as red-flowering gernaiums in terracotta pots all the same size, can look fantastic lined up on a plant stand.
▸ The size of pots and other containers varies from huge half-barrels to tiny pots that are specially made to hang from either walls or brackets.
▸ The imaginative gardener can adapt all kinds of household relics, from cast-off old metal colanders to bread bins (boxes) and even old boots.
▸ If you’re planning to grow edible plants in containers, then the depth will be an important consideration, since plants that are eaten for their roots will need space in which to develop them.
▸ You can purchase some purpose-made containers for specific plants. For example, a strawberry planter is usually a terracotta container with a series of small planting pockets in the sides, which allows you to grow the maximum yield of strawberries in a relatively small space.
▸ Growing bags containing specially formulated potting mix (potting compost) for tomatoes and other nutrient-hungry plants are another option but, in a small garden where the container is clearly visible from the house, it might be more aesthetically pleasing to disguise these plastic bags with a wooden surround or something similar.
If your garden is on a balcony or roof terrace, then weight is an important consideration. Take into account the weight of the container as well as its contents, which will be particularly heavy when wet. So if you plan to grow small trees or large shrubs on a balcony or roof terrace, you should consult a structural engineer for advice first.
▸ If you have very little room to spare in your garden, you can use hanging baskets or wall pots, suspending them on heavy-duty brackets or hooks and pulleys. Remember, however, that these containers tend to dry out extremely quickly due to the large exposed surface area, so they will require watering twice a day in very hot weather.
Choosing Plants for Containers
Virtually any plant can be potted up in a container, as long as it’s well looked after. Some plants may require root pruning every few years (which is, in effect, ‘bonsaiing’), and some may need to have cores of the rootball removed each year. This can be an arduous task when heavy pots or moist potting mix (potting compost) is involved, and it’s better to choose dwarf or smaller-growing specimens. Here are some examples.
▸ Fruit trees — ‘Ballerina’ apples, cumquat, ‘Honey Murcott’ mandarin, ‘Nectazee’ (a miniature nectarine), flying dragon rootstock on citrus or smaller growers such as ‘Lisbon’ and ‘Meyer’ lemon.
▸ Screening trees — dwarf lillypillies, small pittosporums (‘Silver Pillar’ and ‘Tom Thumb’), smaller sasanqua camellias such as ‘Mine-no-yuki’ and ‘Yuletide’, yew
▸ Flowering shrubs — dwarf apricot oleander, dwarf duranta (‘Blue Boy’ or ‘Towards 2000’), Elfin series daisies, ‘Little Lianne’ and ‘Petite’ sasanqua camellias, Japanese barberry, Weigela florida
Edible container plants
Some edibles are easier to grow in containers than others. Avoid cauliflower, celery, corn, parsnip, pea and swede (rutabaga). Among the easiest are the many beans, beetroot, carrot, cucumber, lettuce, potato, radish, spring onion (green onion), silverbeet (Swiss chard), tomato and zucchini (courgette).
Capsicum (pepper), chilli and eggplant (aubergine) are not difficult but require warmer temperatures and more sun in order to ripen. Blueberries, raspberries and strawberries are among the easiest edibles to grow in a container. Tree fruit such as ‘multigraft’ apple trees, which have two or three varieties on one dwarf rootstock, are ideal.
▸ You can use groups of pots for greater impact or to conceal an unattractive feature — pots of different shapes and sizes can look better when grouped together, and they’re also easier to water.
▸ The arrangement and placement of plants is important in achieving an overall, pleasant effect. Pots should be uniform, all terracotta or all plastic, for example, not a mixture. Place them in some logical order, perhaps grouped around a feature plant in a large central pot.
▸ For added height, upturn an empty pot and use it as a pedestal for another.
▸ Raised pots look great when trailing plants are allowed to cascade from them — one beautiful, well-planted urn on its own can make a stunning focal point in your garden.
▸ For a classically formal look, position a matched pair of pots on either side of an entrance, pathway or stairway.
Add interest and beauty to a pergola by festooning it with hanging baskets bursting with flower and foliage.
▸ When choosing plants, take into account the conditions in your garden. A sunny, exposed site may be perfect for a Tuscan theme with Italian lavender in terracotta troughs.
▸ Window boxes or troughs are the ideal shape for those long narrow spaces in smaller gardens.
▸ To add height, grow potted standard bougainvilleas, which flower for months and love basking in the sun, as do potted gerberas.
▸ For a damp and shady position, try planting begonias, dwarf arum lilies, ferns and impatiens.
Deep containers are ideal for growing large bulbs, perennials, shrubs and small trees, while wide, shallow containers are useful for small-growing plants, such as alpines, annuals, slow-growing succulents and many small herbs.
Choosing a potting mix
With container-grown plants, a good-quality potting mix (potting compost) is essential for success. Modern potting mixes are clean and weed- and disease-free, designed to be fast-draining yet moisture-retentive; because they are relatively lightweight, they make it easier to move pots from place to place.
There are specially formulated mixes for plants with specific needs, such as African violets, cacti and orchids, and also mixes for specific uses, such as hanging baskets or terracotta pots — these are more moisture-retentive to suit their particular purposes.
Preparing potting mix (potting compost)
To keep them in good condition, container-grown plants benefit from a good, loam-based potting mix combined with a measured amount of base fertiliser. It’s easy to mix this up yourself.
1 Loam-based mixes consist of 7 parts sterilised loam, 3 parts medium-grade sphagnum moss peat, 2 parts grit or sharp sand, plus a base fertiliser.
2 Start by mixing the loam, peat and sand together until they form a uniform mixture. Then draw the resulting mix into a heap.
3 Sprinkle the base fertiliser over the heap and mix it in until there is no visible trace of the fertiliser.
Good-sized drainage holes in pots are vital, as even the best potting mix (potting compost) won’t drain if there is nowhere for the water to go. Avoid pots with drainage holes that seem too small for the volume of soil they will contain, unless you have the tools to drill more.
Never let pots stand in saucers of water. Small pots, in particular, easily become waterlogged from below. Raise the pot on bricks, stones or pot feet, which are available from nurseries. Raising the pot allows excess water to run away freely, minimises water damage to the bottom of the pot and the surface on which it is standing, and deprives critters of somewhere to live.
Potting a Plant
Always match the size of the pot to the size of the plants it will contain, bearing in mind that plants grow. If you’re planting annuals from seedlings that are 5–6 cm (2–2½ in) tall but will soon grow into flowers 40 cm (16 in) tall, choose a pot suitable for the mature size, not the seedlings. But if you’re planting a slower-growing shrub or tree, it’s better to pot it up progressively each year or two than to plant it into a very large pot at the outset. Small plants in big pots cannot use all the food and water available.
Potting mixes (potting composts) contain little or no plant foods, so blend some into the mix at planting time. The amount varies with the size of the pot and the type of fertiliser but in all cases it’s better to be stingy rather than generous, as too much fertiliser can kill plants. Not enough fertiliser just makes them grow slowly and is easily rectified. If you are unsure about this, read the directions on the fertiliser packet before buying. Choose a brand that explains how much to use in various sized pots. Slow-release fertilisers are a good choice for containers as long as you remember when to replenish them.
Pot plants so they are no deeper in the new potting mix than they were in the pot in which you bought them. To achieve this, partly fill the pot with potting mix, then sit the plant in it, adding or subtracting potting mix until the level is right. Unpot the plant and check that the roots are not spiralling around the base. If they are, gently tease them out. You can trim any that are overlong with sharp, very clean secateurs. Place the plant in the new pot and fill it with potting mix to within 2 cm (¾ in) of the rim. Gently firm the mix around the roots, but don’t compact it or there will be insufficient aeration. Water the plant in well.
Try to choose the right pot for the plant and keep everything in proportion. The best container size for any plant is one that is roughly 5 cm (2 in) larger than the diameter of the rootball, and roughly 10 cm (4 in) deeper. After a year or so, depending on the speed of growth, you will need to repot the plant into a larger container. Planting a small plant in a much larger pot is not a time-saving solution, as plants do best in pots only slightly larger than their rootball. Check regularly that the roots are not growing through the base of the pot. If they are, it is time to repot.
Don’t water potted plants according to a schedule. Instead, water when they need it. This will be much more often in summer than in winter, in sun than in shade, in porous than in waterproof pots, in smaller than in bigger pots, and in a windy than in a sheltered spot. To test whether water is needed, feel down into the top 3 cm (1¼ in) of soil. If it is quite moist, don’t water, but if it feels just damp, go ahead. You’ll soon get to know the watering needs of your different pots and won’t have to feel the soil. Generally speaking, don’t allow the potting mix (potting compost) to go completely dry, as it can then be quite difficult to re-wet.
Over time, potting mixes can become water repellent and no matter how much water you apply, most runs straight through to the bottom and the mix remains dry (although the surface looks wet). To test for this, water thoroughly and then, after the water has drained from the surface, scratch the soil in several places. If it is dry underneath, give it a good soak.
If you do allow a plant to dry out to the point of wilting, you can usually revive it by plunging the entire container into water. Hold it down so that the potting mix (potting compost) is beneath the water level, and keep it submerged until any air bubbles stop rising. Remove and allow to drain. The plant should then revive.
Only apply fertiliser during the growing season for that particular plant. Most plants grow more vigorously from spring to mid-autumn and do not need fertiliser from the end of summer until early spring, but they do need water. Some plants are dormant or at their least active during the hot months of the year and grow during autumn, winter and early spring. Feed these in autumn and in early winter.
Always apply fertiliser to moist potting mix (potting compost), never to dry, and always at the recommended rates — more fertiliser does not equal more growth; in fact, it makes the soil salty and toxic. Slow-release fertilisers can be very convenient, but you can also use complete plant food or soluble or liquid fertilisers. Its actually a good idea to alternate between types.
Remember, the more you water, the more fertiliser you will have to apply. The best way to give it is in frequent but very small doses — say, a quarter strength four times as often.
Fertiliser release rates
It’s useful to know the rate your fertiliser will release into the soil. Release rates are as follows: slow-release, 14–21 days; liquid feed, 5–7 days; quick-acting, 7–10 days; and foliar feed, 3–4 days.
Plants that have outgrown their containers should be potted on (or potted up), which is best done either in early spring or early autumn.
▸ Remove the plant from the pot and examine the roots. If you don’t water it for a few days beforehand, then the soil will shrink and it will be much easier to extract it. If you see much more white (roots) than black (soil), or roots protruding strongly from drainage holes, then it’s definitely time to pot on.
▸ Tease out any compacted or spiralling roots, and trim any that are overlong and looking unhealthy.
▸ Replant into fresh potting mix (potting compost), in a pot that is one size bigger than the existing pot.
▸ Water in well and place the plant in a bright but shady and sheltered spot for a week so it can recover before you move it to its new or original location.
If the plant in question is already in a large enough pot, then scrape a way about 3 cm (1¼ in) of potting mix from all around and replace the plant in its original container with fresh potting mix poured around the outside. This process is called repotting as it does not involve a bigger pot.
Supporting smaller container plants
Supports benefit not only potted climbers but also some weak-stemmed annuals and perennials. Perennials such as daisies and pelargoniums will benefit from some form of ring staking and the plants will eventually bush out, disguising the ring support. Other useful staking devices are twiggy bits of brushwood inserted around the perimeter of a container, or metal-linked stakes that fit together to provide a containing girdle for your plants.