By Dr Ann Marks
For hundreds of years camellias have been successfully grown in containers. In China tree sized plants are still to be seen growing in tubs in the courtyards of early Buddhist Temples. In Japan where ground space is at a premium container culture is extensively practiced and societies are devoted to the growing of bonsai camellias.
Modern living conditions often mean little or no garden space, soil quality may be quite unsuitable or the camellia enthusiast may wish to grow ‘just one more’ all these problems may be solved by container culture. Some-times a trial period is of value in deciding the best permanent position for a plant or evaluating its various qualities and, again, growing it in a pot may be the answer.
In some ways container culture makes camellia care easier but it also means your plant is totally dependent on you for its welfare. Resist the temptation to have more plants than you can care for.
Choice of Plant
It is wise to consider the normal growth habit of any plant for which long-term container culture is planned. Pruning will limit the size and shape of your plant but it is easier to work with nature rather than fight against it – the plant will be the loser!
Camellias with slow, compact and bushy growth are best suited to tubs and the choice such plants is wide. The new ground cover sasanquas such as ‘Marge Miller’ and ‘Classique’ may be grown but, in general, this group is naturally rapidly growing. Many japonicas, hybrids and species make splendid container plants. Do seek advice about any plant you may wish to grow and consider those varieties with multiple small flowers. Reticulatas are not recommended for long term container culture due to their rapid, open growth.
Choice of Container
Containers come in a range of shapes, sizes and materials including wood, porous terracotta or earthenware, impervious plastic or glazed ceramics, concrete or metal. Choice is a matter of individual taste but it should be remembered that really good drainage is essential whilst the container should be so shaped that re-potting is readily accomplished—the pot should taper towards the bottom.
The weight of the container is important—a large plant in a terracotta pot is not readily moved. Plastic pots offer the advantages of good drainage, shape, lightweight and, by no means least, economy. Be aware, though, that plastic does absorb heat and protection from hot sun is needed. A simple method of ensuring this is double potting of vulnerable plants. Different materials create differing conditions so it simplifies matters if a collection of plants is housed in similar containers.
The key requirements are that the mix be free draining yet able to retain sufficient moisture to enable the plant roots to find water and nutrients. It must also act as an anchor for the plant by providing support for the roots.
Aeration is important as most oxygen is supplied via the plant roots. Water logged potting mix will result in a lack of oxygen as spaces in the potting mix fill with water and thus lead to poor or retarded root growth and possible death of the plant.
A mixture suitable for tub culture can be easily made from a ‘premium’ potting mix, available commercially, mixed with one part peat moss or coir peat. Such a mixture drains well whilst the added peat keeps the roots cool and moist. Any mixture breaks down over time with increase in acidity. Ideally a pH of 5.5-6.5 should be aimed for with 6.5 preferable initially as pH level tends to fall with the use of acidic fertilizers.
Premium quality potting mixes usually contain fine pine bark and include a slow release fertilizer and water saving granules. Any mix should contain plenty of organic matter, material that will hold moisture and help create an open mix allowing space for air around the roots.
A number of growers prefer to make their own potting mix and though many different combinations are preferred they all follow the basic fundamental principles. A good mix should provide good drainage, moisture retention and adequate aeration and at the same time anchor the plant and provide nutrients to the roots.
Ingredients used in making a mix include bark, untreated sawdust, compost, peat, sand, pumice and perlite. All organic material should be well composted and the addition of a slow release fertilizer is beneficial. Where the mix has a high percentage of compost and bark the addition of dolomite lime improves the pH and makes magnesium more readily available to the plant.
It is recommended that all container grown plants have the same potting mix as this greatly simplifies watering and feeding.
Planting in a Container
It is important not to plant a camellia in too large a pot as the plant will only absorb the moisture it needs and the excess wet mixture in a large container could encourage root rot. However, as the plant grows progressively bigger pots are needed to enable root growth sufficient to sustain the developing plant.
Potting mix, no matter how good, does not last indefinitely and after a period the developing plant will have extracted the available nutrients. It is far better to anticipate your plant’s requirements rather than wait until its health is impaired. There are no firm rules as to when to re-pot. The container needs to be large enough to allow the root ball to develop and the plant to flourish and it should relate to the size of the plant so the plant does not fall over in the wind. Many growers re-pot each plant they add to their collection to ensure all plants are grown in their preferred potting mix.
In general re-potting should be considered every two or three years. Rapidly growing plants and those in small pots will need more frequent re-potting than those with a slow growth rate or in larger sized containers. If in doubt as to the need to re-pot carefully knock the plant out of its container and examine the root system. If there are numerous roots visible on the surface of the potting mix and other roots extending to the base of the container and even growing through the drainage holes the plant is clearly outgrowing its home.
Potting or re-potting may be done at any time but is best carried out in late autumn or winter when the plant is dormant although it may be in flower. Should potting be required at some other time select a cool day, give the plant a thorough watering and choose a shady location in which to work.
It may be necessary to bare-root a camellia. Do this by placing it in a container of water to remove the old potting mix. Prepare the pot by placing drainage material in the bottom or fine mesh over the drainage holes [to prevent the mix washing out] then put some mix in the bottom of the pot and place the bare-rooted plant in the centre of the container and whilst retaining hold of the plant add more potting mix until the plant is secure. Firm around the roots with your fingers, taking care not to damage the root structure. Tamp around the perimeter, making sure that the plant is no deeper than it was before. Allow plenty of space between the top of the pot and the mix to allow for deep watering.
Once you are happy with the size and shape of your plant only general maintenance is required from year to year. This may involve root pruning and/or top pruning. Root pruning involves taking the plant from its pot and with a sharp knife removing 4-5 cm all around and under the root ball. The plant is then returned to the pot and fresh mix added. To compensate for the root loss the plant should be pruned back to about two thirds of its size.
Before disturbing a plant it should always be well watered and afterwards given an application of root stimulant such as “Plant Starter”. Follow this with a little extra care to allow it to re-establish itself.
Every camellia grower has a favourite fertilizing programme. A general rule applies when using liquid fertilizers, use at half the recommended strength as fertilizer burn may occur because of the restricted root ball.
Suggested programmes are:
A nitrogen rich fertilizer such as fish emulsion in August before the on-set of new growth repeated at monthly intervals until November. A fertilizer high in potassium, to promote bud development, until March follows this.
A regular monthly feeding starting in August at half strength of a soluble complete fertilizer. Slow release fertilizers such as 8-9 month Osmocote. Some pellets are placed under the root ball at re-potting and mixed in and some pellets are sprinkled on top and lightly covered. Other slow release fertilizers such as cow manure and blood and bone may be used initially and then incorporated in mulch in subsequent years
Care should be taken when watering containers. There is a temptation to water too often; on the other hand they should not be allowed to dry out. As with most other plants one or two good soakings a week is better than light, patchy applications. On hot days camellias enjoy a cool shower at the end of the day but never water the foliage while the sun is shining on it or leaf scorch will result.
Overhead watering of containers is not efficient, as the foliage tends to act as an umbrella, with the water, more often than not, falling to the ground. A watering wand attachment on a hose allows containers to be filled to the brim so that the entire potting mix is soaked from top to bottom. This flushing will help to rid the mix of any salt build-up, also encouraging the roots to use the entire container and not remain just below the surface.
The location of the containers will affect the frequency of watering. Those exposed to sun/wind will demand more frequent attention.
Mulching is to be recommended especially during time of drought. Not only does it help in water conservation but the plant derives the added benefit of valuable nutrients released during the gradual breakdown of the mulch.