Cacti should be watered thoroughly and then allowed to dry out completely before watering again. In the active growing season (spring and summer), this typically means watering every two to four weeks depending on pot size, compost type, temperature, and light level. In autumn and winter, most cacti should be watered very infrequently, if at all: once a month or less in winter is sufficient for most species, and some cacti benefit from being kept completely dry from October to March. The most common cause of cactus failure in UK homes is overwatering, particularly in winter.
Why Cacti Need to Dry Out Completely Between Waterings
Cacti evolved in environments where rainfall is infrequent but often intense, followed by extended dry periods. Their root systems are adapted to absorb water rapidly after rain and then tolerate complete dryness. Unlike most tropical houseplants, cacti do not have the root cell mechanisms to cope well with constant moisture. Roots in persistently damp compost develop rot rapidly and cactus root rot often kills the plant before any above-ground symptoms become obvious. The plant may appear normal on the surface, while the roots have already completely rotted.
Watering a cactus when the compost is still even slightly damp is the most common cause of cactus death. The compost must be genuinely dry throughout before the next watering. In a terracotta pot, pushing a wooden skewer into the compost and feeling whether it comes out dry provides a reliable indication. The pot should also feel noticeably lighter when the compost is dry compared to just after watering.
Watering Frequency by Season
In spring and summer (March to September in the UK), water thoroughly when the compost is dry. Depending on conditions, this is typically every two to four weeks, but check the compost rather than following a fixed calendar. In a warm, bright position, compost dries faster. In a cool or poorly lit position, drying takes longer. Water less frequently in these conditions to avoid overwatering.
In autumn (October to November), begin reducing watering frequency significantly. In winter (December to February), most desert cacti should be kept almost completely dry: one light watering per month at most, or none at all for the coldest months, is appropriate. A cool, dry winter rest encourages the production of flowers in spring for species that flower based on this seasonal cycle. Keeping cacti too warm and too wet in winter prevents flowering and weakens the plant over time.
How to Water a Cactus Correctly
Water deeply and thoroughly when you do water, ensuring water drains freely from the drainage holes. Water should wet the entire root zone rather than just the surface. Bottom watering (placing the pot in a shallow tray of water for twenty minutes and then allowing it to drain) ensures the compost is thoroughly wetted. Empty the saucer after twenty to thirty minutes: do not leave cacti sitting in standing water.
Use free-draining compost specifically formulated for cacti and succulents, like our Desert Mix.
Signs of Overwatering vs. Underwatering in Cacti
Overwatered cacti develop soft, mushy sections (particularly at the base), may turn yellow, brown, or translucent, and the base may become soft and collapsed. These symptoms often indicate root rot has already progressed significantly. Underwatered cacti become shrivelled and wrinkled, may lean or feel loose in their pot (dry roots contract), but otherwise retain their structure. An underwatered cactus recovers quickly with thorough watering; an overwatered cactus with root rot requires more intervention. If rot is detected, cut back to healthy tissue, dust cut surfaces with cinnamon or sulphur powder, allow the cut to callous for a few days, and then repot into dry, fresh compost.
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