If anyone has ever told you that cacti and succulents don't ever need much water be assured that they are dead wrong. It is a widely believed myth that cacti and succulents need very little water, if any, and that cacti in particular can go forever without it. It is usually assumed that cacti in the desert never receive any water and if that's the case they should be kept dry when we grow them in pots. That is not correct. In the desert a small plant may have roots spreading far around it (not confined as they are in plant pots) and when there is no rain for long periods, these wide spreading roots make good use of heavy dew (or in some areas sea mists). In pots the plants do not have access to this natural moisture unless we supply it.
Assuming your plants are getting the proper light they require, (some need full sun, some filtered sun and some no sun at all but still bright light) and assuming that your potting soil is very well draining with added grit or coarse sand .. this is how your succulents should be watered.
Succulents should never be given just 'dribbles' of water .. or watered when the owner thinks the plant hasn't been watered for a while and feels guilty for neglecting it .. or watered on a weekly or monthly schedule. The plants need to be thoroughly watered when they need it. By thoroughly watered I mean watered until the water runs out the bottom of the pot. The water needs to reach all the roots in the pot otherwise some of those roots will dry up and die. Repeated die-off of the roots from lack of water (drying up) or too much water (rotting off) will stress the plant and set it back from growing normally and could also affect whether or not the plant flowers. If this happens over and over again you sooner than later have a very weak plant which will eventually die or be open to all sorts of disease and pest problems.
After thorough watering, excess water in the pot saucer should then be discarded. When the plant needs to be watered the next time is only when the soil has almost but not entirely dried out. You can either use a pH meter to test the moisture in the soil or as I have suggested many times before, find a flat stone and put it on the surface of the soil. When you lift it, if there is moisture under it, it is not time to water again. If the area is dry it is time to water agai
Most cacti and other succulents have their growing period in Spring and Summer. Spring is the time to begin full watering providing the weather is warm both day and night. Rules also sometimes have to be mixed with a little common sense. If it happens the weather is still chilly outside but you see signs of life and new growth on a plant that's the time to begin watering it.
What about spraying your plants? Most cacti and succulents do not appreciate a humid atmosphere. There are exceptions but even these do not like prolonged humidity in the air. You can give your plants a very occasional light spraying with warm water on a warm day and preferably in the early morning to give the plants time to dry off by night time. I do this twice a year. Once in spring when the plants are going to wake up and I feel a light misting helps get rid of any dust that may have settled on them over winter. Again at the end of summer for the same reason. Just to clean them off a little.
Spring and Summer growing plants will tend to want a rest after their growing season. As days grow shorter in the fall, begin to reduce watering as the plants, at rest, will not be taking it up as they did when in full growth. A little water in winter to help avoid roots dying off is all that is needed if the plants are grown in a warm house or heated greenhouse. If they are in a cold greenhouse even less water is needed and in some cases none at all. One must research the needs of each plant to know if your plants will enjoy a cold greenhouse in winter and how much if any water is needed at that time.
Some cacti will tolerate and even prefer a very cold greenhouse say down to about 40F to 45F. They are best not watered while at that temperature because that degree of cold combined with wet invites rot. This seems to contradict what I said about not letting the roots dry out and die. The problem is that if the plants are in a very cold greenhouse - cold and wet promotes rot. These plants may lose some of their roots but will quickly produce them again when watering begins in Spring. Where the trouble enters, as I explained before, is when plants are repeatedly watered (or not) incorrectly, roots are repeatedly killed off by either lack of water or too much of it.
A few succulents grow in fall and winter. Many Aloes are winter growers for example. The watering schedule for winter growing plants begins in Fall instead of Spring and is slowed down in Spring and Summer. And because they are winter growers they need warmth during those cold months of the year. Once again common sense prevails. I have a winter growing plant which suddenly decided to come to life in August. That was my signal to begin watering again.
There are of course exceptions to every rule. Some succulents are very succulent and extra extra care not to over water must be exercised. Some may need a different soil mix which gives even more drainage than the average succulent needs. And epiphytic cacti like Orchid Cactus and Christmas Cactus should never be allowed to totally dry out.
Finally .. Never water any cactus or succulent plant on a dull, overcast or rainy day.
Never water a sick plant.
Major requirements for cacti and other succulents:
Plants must be grown in sufficient light. A dark place in the house is no good. Sometimes a bright window is fine but that again depends on the plant. Some must have full sun (not just on one side of the plant) all day long all year long. If you don't give your plants the light they need they will not do well and most likely will not flower.
Soil must be really well draining so water can soak through, the excess comes out the bottom of the pot and the soil left moist but not soaking wet. But what is soaking wet and what is moist? Think of a sponge filled with water - that is soaking wet. A sponge wrung out is left moist.
Once you have your soil mix ready, take up a handful and squeeze it. If it stays together it needs more gritty material to loosen it up. If it falls apart in your hand, you've got it right!
Never use soil from your garden!! Never use soil that is more peat than soil as many houseplant mixes are sold today. Too much peat makes the soil far too acid for most succulents with the exception of Orchid cacti and Christmas cacti and even these do not want more peat than soil in the potting medium.
Lots of warmth during the months the plants are in growth. Warmth in winter for those that need warmth year round .. or a cooler temperature in winter for those which prefer cooler conditions when they are resting.
Proper watering as already explained.
Plenty of fresh air should be available to all plants. In winter ventilate once in a while by opening a window (put a sweater on if you have to) but don't sit the plants in a draft. If you would be uncomfortable in the same situation, so will the plants.
Plants need food
Nutrients in the soil are taken up and used by the plant and when these are gone, if you don't feed the plants they will starve. Succulents do not like a high nitrogen fertilizer which make them grow lush and flabby. Use any good houseplant fertilizer (with trace elements) and dilute to 1/4 strength recommended on the label. Feed at least once a month during spring and summer. For large, vigorous growing plants such as tall columnar cacti, a stronger mix of fertilizer should be given. Some say full strength but to be on the safe side I use half strength and feed with every watering. Every watering for large plants is about once a month because it takes that long sometimes for the soil to almost dry out after a thorough watering. This stronger feed also applies to many caudiciform plants.
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