Here are some tips for the care of your succulents.
All plants need water in order to survive. Too little water, and the roots will dry out and the plant may eventually die; too much water, and fungal diseases may appear. So it is important to know how much water each species needs. If in doubt, hold back on watering.
In the summer
Contrary to popular belief, succulent plants need quite a bit of water in summer, because that is their period of active growth. They need to be watered deeply, and the soil should be allowed to dry out almost completely between waterings. Plants grown outdoors in summer will require more water than those kept indoors. Never place a saucer under the pot of a plant grown outdoors, for water will pool in the saucer.
During fall and winter
In late summer and early fall, gradually cut back on watering. In late fall and in winter, it is best to allow the plants to go dormant by keeping them dry and cool. Plants kept at temperatures below 12°C in winter should not be watered at all. After a period of dry rest, resume watering gradually.
Most succulent plants require bright light. This is why it is best to grow them outdoors in summer. With a few exceptions, mature plants require full sun. A few genera, including Gasteria, Haworthia and Sansevieria, require bright but indirect light. Young plants should be protected from full sun when grown outdoors.
Plants should be placed in the brightest windows in your home—a south- or west-facing window is best. The light may be too strong for some plants in spring (March-April) and summer, however, causing the foliage to become discoloured or scorched. An east-facing window is best at those times.
Succulent plants overwintered at temperatures below 10°C require very little light. Some, like Cereus, can even be stored in the dark all winter long at low temperatures (8-10°C). Some plants with a winter growing period that are native to the southern hemisphere, like lithops, require bright light and lots of warmth for part of the winter. Artificial lighting should be used to supplement natural daylight in this case.
During the summer, optimal growing temperatures are 25 to 35°C, and about 10°C lower at night. Most succulent plants tolerate both very high (over 40°C) and low (under 10°C) temperatures. Some can withstand light frost, while others, like Opuntia humifusa, will tolerate heavier frost.
In late fall, most succulent plants enter dormancy (in the northern hemisphere, at least). To encourage dormancy and the initiation of flower buds, cacti and agaves should be kept cool, between 6 and 12°C, while other succulents require 10 to 15°C temperatures. Dormant plants must be kept dry, in a spot with little relative humidity, because the combination of cold and damp is conducive to rot.
When to fertilize?
Succulent plants require nutrients, but in smaller amounts than most indoor plants. Fertilizer should be applied only in spring and summer, the active growing period, at two- to four-week intervals, at approximately one-quarter to one-half the dosage recommended on the label. No fertilizer is required from mid-September to March.
Which fertilizer to use?
You can use organic or synthetic fertilizer. Leafy succulent plants, including Crassula and Aloes, require either a 20-20-20 type all-purpose fertilizer or a seaweed-based organic fertilizer (e.g. 3-7-5) alternating with fish emulsion (e.g. 5-2-2) or seaweed- and fish-based fertilizer. Fertilizers used for plants with needles or spines should be low in nitrogen but high in phosphorus and potassium.
There are fertilizers specially designed for succulents (2-7-7), but formulations like 15-15-30 (tomato food) and 15-30-15 are fine, too. Seaweed-based fertilizer is also appropriate for this type of plant. You may wish to occasionally amend the soil with calcium sulphate (gypsum) to help keep the needles and spines firm.