Container gardening is presently very fashionable but it is nothing new; it has a history stretching back to Classical times and the earliest days of horticulture. It still offers a very versatile way of growing plants, for almost any type can be grown in a container if the correct planting medium is used. On the one hand, containers may constitute almost the entire garden for those with very confined space, and on the other, they can be used instantly to change the appearance of a much larger area. Nonetheless, the choice, handling and indeed the limitations of containers are the same. Plant roots are restricted to the moisture and nutrients they can obtain from the small volume of, so more care in watering and feeding is needed.
And as container gardening involves more work, it is usually reserved for plants that have particular merit – unusual foliage or a very long flowering season, for instance.
Some of the principles of container gardening are also applicable to small, table beds and peat beds.
Size and shape of containers
A visit to any garden centre will reveal a huge array of containers, varying in size and shape, and manufactured from a wide range of materials including terracotta, wood, concrete, reconstituted stone and various types of plastic. Aesthetic considerations and cost will play a major part in dictating your choice although, in general, plastic is the cheapest, least attractive and functionally has perhaps the greatest drawbacks.
There are certain features that are important when containers are being used. First, therefore, I shall consider free-standing containers and will suggest some of the aspects that you should take into account when making your choice.
A cubic metre (cubic yard) of potting compost weighs approximately 1 tonne (1 ton). If you plan to move full containers, therefore, the size of the container and the volume of compost it will contain become very important considerations. I find that a terracotta tub about 40cm (16in) tall and 36cm (14-1/4in) in diameter is the maximum that I can move comfortably. Concrete containers of the same size will, of course, be proportionately heavier. Conversely, many containers, although superficially attractive, are too small or shaped such that they contain too small a volume of compost to be functionally effective. They fail partly because they require watering unrealistically often and also because there is insufficient space for the roots of a plant with large enough leaf and flower growth to be attractive. Some concrete containers, for instance, appear fairly large externally but have very thick walls and a limited internal space. Some of the containers sold for attaching to walls also contain very small volumes of compost and flat-backed wall pots are, in my experience, particularly troublesome. In general, I would advise against choosing any container that had an internal volume less than that of a conventional plant pot, 20cm (8in) in diameter.
Stability of free-standing pots is another important consideration and is a function of several features: height, the ratio of height to diameter, volume of compost, type of compost (a-based compost is very much heavier than the equivalent volume or a soilless one), size of plant and relative exposure and windiness of the site. Again, I can only advise on the results of my own experience and suggest that the most important feature when choosing a stable container is to avoid those that taper sharply downwards and have a basal diameter less than about two thirds that of the top; the taller the container, the more important this ratio becomes.
I would never, for preference, choose a plastic container; they will always look like plastic containers and thus inferior, they are easily damaged if moved when full, many types discolour and become more brittle with age and they suffer from the important drawback of being impermeable to water and air. Any plants grown in them are likely to suffer from water logging and consequent root damage. They do, of course, have the advantage of being relatively cheap, so you can certainly buy a large number and so immediately colour a new garden at a time when there will certainly be more pressing demands on your funds. I suggest, therefore, that if you must begin your container gardening life with plastic pots (or even with really make-do vessels such as old paint cans), you should gradually replace them, one or two per year, with more attractive and traditional types.
Unglazed earthenware called terracotta has been used to make plant containers for centuries and is undeniably lovely, if expensive. But choose carefully; there are some very attractive pots imported from warm countries that cannot tolerate even a slight degree of frost without flaking or cracking. These must, therefore, be taken under cover in the winter. The frost tolerance of terracotta depends on the nature of the clay used and the way that it is fired. Some manufacturers are now so confident of their materials that they offer a 10-year guarantee of frost resistance so their pots can safely be planted with perennials and left outdoors permanently. Use your non-hardy terracotta pots for plants, such as specimen, that must themselves be taken into the protection of greenhouse or conservatory in the winter.
Troughs or other containers hewn from natural stone are beautiful but now extremely scarce and prohibitively expensive. Their place has been taken by moulded concrete and reconstituted stone vessels, some of which are very difficult to distinguish from the real thing. Check that these containers too are frost tolerant and that they don’t contain a chemical setting or hardening agent that is toxic to plants until they are well weathered. The easiest way to encourage the growth of lichen and algae, and so simulate more closely a genuine old stone container, is occasionally to paint the concrete with milk or liquid cow manure.
Wooden half-barrels offer easily the cheapest way of obtaining really large containers but should be painted inside and out with a nontoxic preservative before use. Also, remember to drill several drainage holes in the barrel before they are filled with compost. It is very difficult to move a half barrel full of compost but, if it must be done, try using three rollers cut from lengths of old scaffolding pipe.
And so to types of container other than those free-standing in the garden. Window boxes are a special delight in inner city gardens (provided they are out of reach of vandals) and for apartment dwellers. Much the best system is to invest in wooden boxes – which may have to be specially made — of the exact size and shape of your window ledge and with drainage holes. These should be treated with non-toxic preservative inside and lined with plastic sheet also pierced with drainage holes. Within this wooden frame, you may then place plasticand pots containing the plants. This arrangement allows you to plant up the containers (and even allow the plants to mature) before placing them on view and also gives you the flexibility of replacing individual pots or troughs during the summer.
Hanging baskets present special difficulties. Their weight when full and wet should be a major consideration and support brackets must be strongly anchored. For reasons of weight if none other, soilless compost is much to be preferred and drainage should be free but not so liberal that the whole requires watering more than once each day. Composts are now available that incorporate moisture-retaining gels in order to cut down still further the frequency of watering. Some restrictive liner is necessary in any hanging basket to prevent the compost from falling out, and, while the natural sponginess of sphagnum moss is ideal, it is now difficult or costly to obtain and the easiest method for the modern gardener is to buy wool or similar fibre-based alternatives. Many modern baskets are too shallow to be effective and the compost inevitably dries out very rapidly; a basket should be at least 30cm (12in) in diameter and at least 18cm (7in) deep.
The choice of compost for containers (apart from hanging baskets) is relatively straightforward. If the plants are to be grown at least semi-perennially, by which I mean for more than one season, use a soil-based potting compost such as John Innes No. 3, although for alpines, a more gritty mixture is preferable. If they are to be grown asfor one season only, use a soilless potting compost. But always remember that the nutrient reserves of a soilless compost are less than those of a soil-based type and that the liquid feeding which is essential for all plants in containers should begin for them after about 3 weeks, whereas a soil-based compost should be adequate for twice this long before a supplement is needed.
And once the plants are established, bear in mind that with no water reserves to tap at depth, watering at least once and preferably twice a week (with a once-a-week feed) is essential for tubs; and watering once a day with twice weekly feeding is the regime for hanging baskets.
Growing-bags are discussed again tinder the subject of vegetables but although popular to some extent for annual ornamentals, they have serious limitations. In a greenhouse, I much prefer the ring-culture system of raising tomatoes and similar plants and urge all greenhouse tomato growers to consider this very seriously. Growing-bags are useful, however, for tomatoes,and similar crops outdoors on paved areas where there is no access to bare soil and there are now several proprietary ways of overcoming the difficulty of providing staked support for plants raised in this way. Apart from this, the plastic growing-bag has for long had a major drawback in that watering is very hard to regulate. It is impossible to see if the compost is wet or dry and plants can easily suffer from both extremes.
Recently a number of ingenious ways have been devised to overcome the problem of watering. The most effective of those that I have tried entails using a small transparent water reservoir with a tube that is pushed into the side of the bag. It will keep the compost fairly uniformly moist for several days and it is easy to see when the reservoir itself needs replenishing.
Containers need drainage holes at the bottom, so you should place a few stones, or old crocks if you have them, over the top of the holes. Add the compost, breaking if up if it has become compressed in the bag. Water the plants in their original pot and leave them to drain before planting. After planting, press down the compost so the level is 3-4cm (1-1/4in) below the rim of the container, otherwise water will run off the compost. Large containers can be mulched. Small ‘feel’ for holding the pots off the ground are worthwhile when containers are on paved areas: they assist drainage, prevent staining of the underlying surface and help to discourage slugs and snails
Hanging baskets should be planted up as they are filled with compost. After lining the basket, place a small volume of compost in the base and feed any trailing plants carefully through the sides of the basket from within. You risk damaging the plants if you attempt to push them through from the outside. Gradually fill the container with more compost. Once the basket is about three quarters full, position the top plants starting with the central specimen and working outwards. Strawberry andpots are filled along much the same lines as hanging baskets, but as it is hard to water these evenly, do make sure that the roots are firmly in contact with the compost from the outset.
Winter container plants are becoming ever more popular, but it is important to remember that even hardy plants can suffer if their rootball is frozen over winter, something that can happen in the small volume of compost offered by a hanging basket. Plants grow very little during the winter months and small plants won’t fill out the basket as they will in summer, so use more mature plants; winter-flowering pansies, for example, should already be in flower when they are planted.
Once containers are planted, you will need to water and feed the plants regularly throughout the growing season. All annuals in containers should be watered at least twice a week and summer hanging baskets will need watering daily.
A spray lance attachment to a hose can make watering easier although an alternative, if you have several hanging baskets, is to install an automatic watering system. Long-term container plants will be in a bigger volume of compost and watering need not be so frequent, although a mulch in early spring can also help reduce watering.
Short-term plants like bedding and tender perennials grow rapidly and should be led with a liquid feed around six weeks after planting and this should then continue every week until growth slows down. Slow-release tablets or granules that are inserted in the compost at planting time are popular for container plants but extra feeding with liquid fertilizer is often still needed later in the season. For flowering plants, a fertilizer with a high potash content, like a tomato feed, is suitable.
Summer vegetables grown for their leaves may be fed with a balanced liquid fertilizer, like liquid Growmore, although fruiting crops need a special tomato feed. Again, once a week should be sufficient at first, increasing to twice a week when growth is very rapid. For permanent plants in larger containers of soil-based compost, it should be sufficient to replace the top few centimetres of compost. And always remember that every plant in a container must look its best when on display, so regular dead-heading and removing of faded foliage is important.
Using containers in the garden
The really big advantage of growing plants in containers is the degree of control that you can exercise over them and their environment. Whereas a poor soil takes many years to improve, you can plant up containers with good quality compost and obtain fine and rewarding results within a season. Dull corners can be brightened even where there may be no soil as in a balcony garden or a courtyard. You can position plants where the conditions are ideal for them: those that suffer from exposure can be given, while those that prefer dappled shade can also be accommodated, and so on. Plants can be brought on show when they are at their peak and moved out of the way when they fade.
Gardening with containers allows you to grow and enjoy plants that are wholly unsuited to the type of soil occurring naturally in your garden. By selecting an appropriate compost, you may have acid-loving plants in an alkaline garden or plants that need a free-draining, sandy loam even if your garden soil is wet, heavy clay. And, as you can control the soil or compost within the container, soil-borneare not usually a problem although temporary plants should be planted in fresh compost in clean pots each year.
To integrate them into your overall garden, choose containers that will work harmoniously with your garden style. Rustic or informal containers will enhance a cottage garden but not a formal area. If in doubt, choose a selection of plain terracotta pots, the largest you can afford, which will suit most gardens and planting schemes. A group of containers can be used to sol ten hard surfaces, such as an area of gravel, paving or concrete and a climber in a container can break the bleakness so often found where a wall meets a horizontal hard surface.
While a container can provide much-needed vertical elements in flat gardens, you need to be bold with both your choice of pot size and plants to make an impression. For example, use a collection of small pots with the same repeated planting to create an impact. Small pots, each planted with a bright red, positioned one on each of a flight of steps produces a band of colour and also invites the visitor to walk up the steps to explore the rest of the garden.
In a formal garden, try a container-grown specimen of topiary to provide year-round structure. Grow a fruit tree on a dwarfing root-stock in a large tub in order to obtain fruit from a courtyard garden: use tubs for growing bulbs, (either, as with in the form of a permanent planting or as with and , to provide colour before summer annuals take over); and plant a small selection of pots with herbs to be positioned close to the kitchen. Use tubs or hanging baskets to brighten up your front door; again choose subjects that will work in harmony with your style of entrance. A pair of trimmed container-grown evergreens on either side of the front door can look very stylish and they are easy to maintain.
A tree in a container is a long-term feature that will act as a focal point in the garden, so it is important to choose carefully. It should be-slow growing and have something to offer throughout the year.
You are unlikely to become self-sufficient by relying on vegetables from containers, but it is often useful to have crops close at hand on the patio or by the front door if most of your vegetables are grown on an allotment. I would not trouble with most brassicas,or globe artichokes; the plants are too big for their yield. Potatoes in dustbins in an unheated greenhouse can provide clean, early crops but if you want your containers to be attractive as well as productive, use vegetables like carrots and that have attractive foliage. Tomatoes are a well tried crop for containers and miniature, small-fruited bush varieties like ‘Tumbler’ can be grown in a hanging basket with basil. Peppers look attractive in large pots on the patio but they need staking. Lettuces are quick-growing and work well, especially where they can be grown alongside herbs.
Using containers to conceal unsightly features can be very effective, but if used to disguise a drain or man-hole cover, it makes sense to support the tub or other vessel on wooden battens placed either side of the offending object. It will then be easier to move and will not damage the cover.
Finally, a word of caution for those who container garden in high-rise city apartments. Do ascertain the weight restrictions imposed on your floor; remember that statistic of 1 cubic metre of compost weighing 1 tonne (1 ton).