Cacti are easy-care plants because their feeding and watering needs are low. You can mostly ignore them, and they still thrive. But if you are a chronic overwaterer, cacti may be a source of endless frustration. When your cactus has been overwatered, do not fear; there is a chance you can save it. If no fungal or bacterial rot is present, a neighborhood change may be enough to get your cactus back on track.
Damage Assessment
If you suspect overwatering and damage, such as soft brown spots, are evident outside the cactus, unpot the plant by wrapping a few layers of newspaper around it and tipping it out. Carefully brush the soil from the roots and check them for brown or black areas. Extensive damage may be difficult to detect, but you are in good shape if most roots are white. Cut away the black and brown roots and leave the cactus out of its pot to dry. You must reroot the cactus if brown or black rot areas are extensive. A cactus that has only been occasionally overwatered will recover without further drama.
Encourage Drainage
When overwatering is a chronic problem, help the cactus shed as much water as quickly as possible. Select an unglazed clay pot only slightly bigger than the cactus and fill it with a commercial cactus potting mix. Pot the cactus gently in the mix so you do not upset its delicate roots. The clay pot will wick away more water from the root zone, while the loose cactus mix allows water to drain quickly and thoroughly. You should only plant very large landscape cacti directly in the ground because landscape plantings give you less control over drainage.
Rerooting
When roots or tissues are severely damaged by overwatering, use a sharp, clean knife to remove all cactus rot. Even a small portion of healthy tissue can regenerate a whole plant, but it may continue to spread if you leave the rot behind. Allow the cactus to dry on the counter for several days, until thick scabs form over the cut sections. Then, place the remaining cactus section in a clay pot filled with cactus soil and bury it about 1 inch (2.5 cm) deep, unless not much of the cactus remains. In that case, plant it about halfway. Do not water the cactus for the first week; only water sparingly after that until new growth appears.
Proper Watering
Correct watering is vital to prevent new problems once your cactus is repotted and ready for success. Water the cactus only when the top 1 to 2 inches (2.5 to 5 cm) of soil is completely dry. Do not water the plant from the bottom; never leave it in a saucer of water. The soil should be drier than wet. A good rule of thumb is to water about once every ten days.
Source: sfgate.com
Links
- Succupedia: Browse succulents by Scientific Name, Common Name, Genus, Family, USDA Hardiness Zone, Origin, or cacti by Genus