Plants grown indoors, or in glasshouses, will develop faster and have a better appearance but will be more sensitive to sunburn during the hot periods of midsummer. An excessive build-up of heat in glass covered areas can be avoided by shading and regular ventilation. The brown scarring of the surface tissue is caused by excessive sunlight and heat and, although this rarely damages older plants, it can make cacti less visually attractive.
Alternatively, insufficient light can cause cacti to display pale colouration and result in an elongation of the growing tip and poor flowering.
In their natural environment cacti experience a temperature range typical of cool, dry winters and warm springs. Spring rains are followed by hot summers and the growing cycle for most varieties reflects these conditions.
Plants kept indoors should also follow a similar temperature change during the year. Plants can be kept in a cooler part of the house during winter when the heating is on.
Moisture and Watering
Regular watering should be restricted to the months when there is visible, active growth of the plant. Watering to run-off point once or twice a week is better than watering daily. The soil should be allowed to dry between watering and the body of the cactus should be kept dry. Overwatering can result in poor growth and even death as the waterlogged roots will slowly die under these conditions.
Soil Mix and Fertilisers
Many growers prepare their own special soil mix and opinions vary as to which method is best. The more successful growers use a special mix of soil: well drained and coarse; warmed readily in the sun; allows for easy root penetration and repotting; contains low levels of nitrogen and has balanced levels of other nutrients. A suitable blend for all Mexican or American desert cacti of spherical shape would consist of coarse gravel or crushed brick (50%), peat (25%) and roughly sieved, mature compost (25%). A handful of granulated, slow release, inorganic fertiliser should be added to every 10 kg of soil mix and a small amount of paradichlor-benzene crystals will add protection against the mealy bug.
For many years clay pots have traditionally been used for cacti. More recently, lighter and cheaper plastic pots have been used for solitary plants or mini gardens. The advantages of non-porous pots include reduced moisture loss and even distribution of root systems throughout the soil.
Suitable cacti for your home can be found at most good nurseries. Some establishments have specialists on hand to help you select the most suitable species for your conditions. Your local library is also a good source of extra information and will allow you to identify growth habits and flowers. Cacti are great fun to grow and easy to look after. Why not give your child, relatives or friends a living present this Christmas?