Cactus Cultivation: Watering Cacti, Taking Cuttings and Raising from Seed
Watering the plant presents the most important part of cactus culture. More plants are lost through overwatering than from any other cause. As has been stated before, cacti will not grow without water but if they get too much they can soon die. Newly potted cacti should not need watering for about a week. The pottingshould have been crumbly moist at the time of moving the plant. If it is too wet or too or it cannot be firmed in the correct manner. The whole secret of watering can be described in one sentence. Never water a plant if the soil is still damp. It is not easy to tell when a cactus needs watering. Ordinary plants soon show by drooping leaves when water is required, but cacti cannot show their needs in this way. The condition of the top of the soil will indicate when water is needed. After a hot day the soil may appear dry, but this may only be the top inch. If pots are inspected in the mornings the soil should be of a uniform dampness throughout.
Rain water is better than tap water but if rain water is not available let some tap water stand in the open for a day or two before it is used. Water may be given from a can with a small spout so that it can be directed into any pot. Do not water by immersion except for the first watering after the winter. If plants are watered this way often, all the nourishing matter will soon be washed out of the pot. Cacti may be sprayed in the evening of a hot day. No water need be given from the end of September to early March. Then water when the soil has dried out, not before. The Christmas cactus, Zygocactus truncatus, may be watered during the winter as long as the temperature is not below 50 °F (10°C). Other cacti may be left at 40°F (4°C), so that they get a winter’s rest.
Propagation is by cuttings, taking offsets or by seed raising. Cuttings taken from opuntias and epiphyllums are removed with a sharp knife and the cut part is allowed to dry in the sun. The cuttings are then rested on a mixture of equal parts of peat and sharp sand (not silver sand).
Cactus potting compost may be used to fill three quarters of the pot, with the rooting medium on top. Place in a sunny position and spray occasionally. Too much water must not be given until roots have formed. Tall cuttings will have to be supported by a stick, as they must not be pushed into the medium.
Grafting may be done to assist the growth of a small, slow-growing type. A tall type is used for the stock, such as Trichocereus spachianus. The top is cut from the stock where the growth is new and healthy. The scion is cut at the base so that it is about the size of the top of the stock. It is brought in contact with the freshly cut stock and kept in position with two small weights on a piece of string, pressing the scion clown firmly. Keep in the shade for a week or two and a firm joint will form.
Raising cacti from seed
Some cacti never make offsets and these have to be raised from seed. A small propagating frame can easily be made and heated with an electric cable or even an electric lamp. Half-pots of about 4 inches in diameter are very good for sowing small quantities of seed. They can even be divided with celluloid labels if more than one species is to be sown in the pot.
Use a good seed compost and sieve a small quantity through a perforated zinc sieve. Place the coarse material over the crock and then top up with ordinary compost, having an inch of the fine soil on top. Small seed must not be buried, but fairly large seeds can be just pushed into the soil. Water the first time by standing in containers of water so that the whole soil can be well moistened. Place in the frame with a piece of glass on top and then cover with dark paper. The best time to sow is in early spring, in a temperature of 70 °F (21°C); seeds will germinate at a lower temperature but will take longer to do so.
Once seedlings have appeared, the paper must be removed and the glass should be raised slightly. The seedlings must be kept from the direct sun for the first year but they must have plenty of light or they will become drawn. Do not allow the seed pots to dry out while germination is taking place; watering may be done with a fine spray.
Prick out when the cotyledon or food-bag has been absorbed. Before this the root is so tiny that it can be broken very easily, in which case the seedling would die. The seedlings may be placed 1 inch apart in the cactus compost as described above. Do not pot up too soon into small pots as these dry out very quickly. Boxes made of concrete or plastic are better for the seedlings until they are ready to go into 2 inch pots.