Have you noticed that occasionally some of your plants will get swollen blister like areas on their leaves or fleshy stems? I went through a period of that with one of my Christmas Cactus’ for two years straight. I’m happy to report that it’s not happening this year though.

Sometimes the spots are tan at first or they become dark brown and become wart like. Corky bumps occur most often on the underside of the leaves of succulent plants such as jade plant and peperomia. Of course they could occur these bumps could occur on other plant parts, and on other types of plants as well such as Swedish ivy, schefflera, croton, geranium or begonia.

It this were to continue the leaves will turn yellow and droop, and then fall from the plants. Plants can become spindly and cease to grow as result of this condition which is called edema. It is often found on indoor plants in winter. It’s caused by environmental factors – a build up of water pressure in the leaf tissues will result in dostortion and busting of cells.

Overwatering, high humidity, and low light intensities favor the development of edema. Faulty watering practices, such as allowing plants to dry out completely and then drowning them, encourages it. Avoid overwatering susceptible plants, especially during the winter months when they should be kept slightly on the dry side.

Differences in potting medium, environment, and the individual plant type influence water needs. If the soil feels or looks damp in a pot, don’t water. Allow the soil to dry out somewhat, then water deeply until water drains out of the hole in the pot’s base. This insures that all of the plant’s roots receive water and it leaches out excess minerals accumulated in the soil. Make sure to empty water out of the saucer beneath the plant so the roots do not sit in water.

If edema occurs, keep the relative humidity below 70% in the vicinity of the plants. Improving air flow over the leaves by spacing plants further apart and increasing ventilation will help reduce humidity. Inexpensive humidity meters which can help you monitor the plants’ environment can be bought at garden centers or through catalogs. Moving the plants to a sunny location or adding supplemental artificial lighting is also beneficial.

Leaves showing symptoms of edema will not recover, but you can halt the decline of a plant by improving light and watering less often. Repotting to improve soil drainage may also help. Affected plants often recover from oedema with the return of more favorable growing conditions in spring and early summer, especially if they are placed outside as soon as weather permits.