CULTURE OF BEGONIAS
Where to grow them.
Begonias can be grown in the garden, in pots in a shade house or on a windowsill; they can be grown indoors under lights or in a terrarium. Different types of begonias have differing light requirements. In the garden, semperflorens or bedding begonias are quite happy in the full sun. Cane and shrub begonias need light shading; early morning or late afternoon sun is beneficial. Rhizomatous need slightly less light than the canes and shrubs. They can be grown in sheltered places under trees. The amount of light is important, if they get too much your plants will have small leaves, the edges will burn, and the colour will be bleached. Not enough light, the leaves will become large, the stems long and weak and the plants will not flower well.

Begonias are often grown in a shade house; these can vary depending on the budget and the type of begonia you are growing. I have been growing begonias in southeast Queensland for fifteen years or more in a variety of shelters and shade houses. I have found that a roof covering of clear solar weave plastic under shade cloth of 75% is suitable for canes, thick stems and rhizomatous over the winter and spring. In the summer, an extra covering of either 50% or 75% is needed. For the walls one layer of 75% shade cloth is satisfactory. The plastic on the roof can cause some design problems as to holding water but I find it easier to control the watering when there is no rain to worry about. In other areas of Australia different shading and walls may be needed, in Melbourne less shade is needed in Cairns more in Adelaide the walls may need to be of plastic to keep in the humidity.

POTTING MIXES
There are dozens of recipes for potting mixes, most growers have their favorite basic mix, it may be a commercial mix or made from whatever is available at home. You will probably have to buy a few ingredients such as peat moss or perlite. If you use a commercial mix buy a good quality one, these are usually based on peat or bark and will last longer. The cheaper mixes are often made from sawdust and woodchip, they will rot in the pot, and the drainage will become very poor. If you are using a commercial mix it will probably be adequate for semps or canes but for rhizomatous you will need to add 10-20% perlite to improve the drainage. If you are mixing your own mix a few things to remember, if you use a peat and sand mix, this can be hard to moisten if it has dried out, if this happens, stand the pot in a bucket of water for a while. If you are using compost make sure it is well rotted, if not it will continue to rot in the pot and upset the drainage, also you may have problems with weeds if it is not composted fast enough. Sphagnum moss can be used in some mixes; it can be cut up or rubbed through a sieve then added to the potting mix. You will have to adjust the pH of your mix with lime or dolomite to about 6.5.
The recipe for the mix I use is.
4 parts compost
2 parts peat moss
4 parts fine gravel 2-5 mm
1 part perlite
1part seedling orchid bark 3mm - 5mm
Lime to pH 6.5
This mix is suitable for rhizomatous begonias and will last at least 12 months before repotting. Sterilising the potting mix will save time weeding.

FERTILIZING
You will need to fertilize your plants, especially when you are growing them in pots. Most commercial potting mixes have enough fertilizer to last 2 or 3 months after that your plants will need regular feeding through the growing period. If you are using a compost based mix you will need less fertilizer. There are dozens of different fertilizers on the market, the most commonly used for begonias are slow release, soluble, and fish emulsion fertilizers. Always try a new fertilizer on one or two plants, leave them for a few days to see any adverse effects before using it on all your plants.

The slow release fertilizers are usually dug into the surface soil of the pot; they can also be added to the potting mix before the plant is potted up. They will last for 3 to 12 months depending on the type you buy, be careful with this type of fertilizer, some growers use too much too often, read the instructions on the packet.

There are dozens of different soluble fertilizers on the market, the best way to sort them out is to look for the N. P. K. number this will tell you the amount and ratio of nitrogen phosphorus and potash. Fertilizers high in nitrogen will give lush green growth; sometimes at the expense of the proper leaf colour, also the stems can become weak. A fertilizer high in phosphorus will give strong stems, a good root system, and good flowering. One high in potash will give good leaf colour and improve flowering. This type of fertilizer can be sprayed on the foliage and or the soil. Try using it at half strength every 2 or 3 weeks from spring when your plants start to put on new growth until autumn. Make sure you have watered your plants before you put on fertilizer as it can burn dry roots. If the leaves on your plants start to look limp or burn around the edges stop putting on the fertilizer for a few weeks.
Fish emulsion fertilizers are made from fish by products some have added chemicals e.g. urea other organically based fertilizers may have kelp {seaweed}in them, look for the N. P. K. number as a guide. Always try these on one or two plants first, as they can sometimes burn the leaves especially on some rex begonias.

WATERING
Proper watering is essential if you want healthy begonias; it is easy in the garden. I have set mini sprinklers on mine and water twice a week in the growing period and once a week in the winter. You can set them up on an automatic system without too much trouble. It is not that easy when your plants are in pots, I have yet to see an automatic system that will work with begonias in pots. To keep your begonias healthy the potting mix needs to dry slightly between watering. If you keep potted begonias constantly wet you will have trouble with soil borne fungus diseases, the roots will rot and your plants could die. Different plants need differing amounts of water depending on the size of the plant, the size of the pot, the type plant, the type of pot, if it needs repotting, if it is putting on new growth or dormant. I look at the potting soil of each plant and water accordingly; if I cannot see it I feel how wet it is with my finger. In the winter months I use a moisture meter, this metal probe measures the amount of water in the soil and registers it on a dial. It is hard to tell how wet the soil is at the bottom of the pot without it. I have regular watering days, in the summer it is every three days in the winter months every six. Some plants may not need watering for several weeks in the winter months or when conditions are very humid.

POTTING
Many people have trouble with this task especially when they have plants that should have been repotted several years ago. Repotting should not be done in the winter or when the plant is dormant or semi dormant, wait until it starts to grow in the spring. Young plants are usually easy to deal with, when they have filled the pot remove them from the pot and repot into the next size pot. If it is a cane type or thick stem, center your plant in the pot, and fill with fresh potting mix to the same height as before, if it is a rhizomatous type put the back end of the rhizome against the inside of the pot so that the front of the rhizome has room to grow. When the plants are bigger they can be divided, to do this remove the plant from the pot, shake off the soil, cane types can be cut up making sure there is several healthy new canes on each plant. With rhizomatous types you may have to remove the older leaves so you can see what you are doing, the rhizome can be cut into pieces so that they are easier to fit in the pot, dust the cut ends with a fungicide powder to prevent rotting. The front part of the rhizome will give you a better plant, keep some roots on the pieces of rhizome as bare ones take a long time to put on roots, make sure you do not bury the rhizomes when you repot, if you do the buried part will rot, they should be on the surface of the potting soil. Do not over pot your rhizomatous plants, most like to be a little crowded.

Begonia to be Repotted	Divided Rhizome	Repotted Plant

Older plants can be a problem; you will have to decide whether to go up a size, keep them in the same size pot, and replace the soil or to divide them up into smaller plants. Often older plants will have rot present, in cane types it will be in the root system and in rhizomatous the older parts of the rhizomes sometimes rot away. When this happens with cane types, you will need to remove the plant from the pot, shake off the soil, cut out the rotten parts, and repot in fresh potting mix. With rhizomatous types trim off the older leaves so you can see what you are doing, remove from the pot, and shake off the soil. The plant will probably fall apart if there is much rot present and you will be left with several pieces of rhizome. Cut off any rotted parts of the rhizome and dust with fungicide powder and trim off any dead roots then either pot up into smaller pots or arrange the rhizomes in a pot so that they have room to grow, you can place them around the pot or across it, arrange them so that the new growth at the front of the rhizome will cover the bare part of the rhizome next to it. Make sure the rhizome is on top of the soil; do not cover the rhizome with mulch as it can cause rot.

Repotting into the Next Size Pot	Repotting into the Next Size Pot	Repotted Plant	Water After Repotting

If you have trouble keeping it upright, stake it. I find that bamboo skewers are ideal for the job, push them into the soil and tie to the leaf stems with plastic twisties. Some begonias tend to grow with upright rhizomes these can be a problem, when you repot this type cut off the back part of the rhizome leaving some roots on the front section. Lie these down on top of the potting soil; the roots you have left on the rhizome will keep the plant going until the bare section of rhizome develops roots where it touches the soil. The rhizome will turn and grow upright but it will have good root system, this method of potting will keep it under control if you repot before the rhizome gets too tall. The old bare part of the rhizome can be potted also to make new plants. When you have finished potting, water your plant just enough to settle in the roots into the new potting mix, do not overdo it. Keep the potting soil just damp until the plant starts to put on new growth, then normal watering can start.

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