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Plants are prone to a number of complications, including pests and diseases, and these complications usually have particular symptoms. However, if your succulent is looking worse for wear with lumpy, spotty leaves, you may have something else on your hands: edema.
Formally spelled “oedema,” edema is a condition that affects many plants, including succulents. The condition isn’t caused by any type of bug or infection. Instead, edema is a symptom of abnormal water retention. Edema is most often characterized by small, papule-like spots on the leaves that are raised and either lighter or darker than the succulent’s typical leaf color. These welts form in small clusters when a succulent takes in too much water. The excess water causes cells in the leaf to rupture, and the signature welts are cells that have broken from oversaturation. Although the spots won’t spread and aren’t harmful to the plant, they can affect how your succulent looks and are a sure sign that your plant is getting too much water.
A succulent with too much water in its leaves is most likely suffering from overwatering or poor drainage. Succulents and cacti require well-draining soil, and it’s common for these plants to struggle with edema if their soil isn’t porous. Still, edema doesn’t always come with poor drainage. Scientifically, edema occurs when a succulent’s roots absorb water faster than the plant can use it.
Edema has several noteworthy symptoms that work in stages. Water-soaked spots will appear on your succulent’s leaves in the first stage. These spots will then rise from the leaf to create light, pimple-like growths on the succulent. These spots are harmless and won’t spread but will continue to appear as the plant becomes over-saturated with water.
Over time, these bumps will swell and rupture, and they may appear white and powdery or rust-colored. In succulents, rusty coloration around the ruptured cells is most common. These areas will then callous over and look similar to scab on the plant.
In succulents with woody stems, you may also spot uneven, corky ridges along the stem or swelling near the stem and leaves.
The best way to treat edema (and overwatering) is via prevention. While these tips aren’t a perfect guarantee to keeping your succulents safe from edema and symptoms of overwatering, they’ll still lower the risk of developing edema.
Prioritizing drainage is essential for succulents and cacti, so a good plant parent will always have the tools to optimize drainage when necessary. Cactus potting mixes are great store-bought alternatives to mixing your own soil, but if you can’t get your hands on a cactus-specific mix, you’ll need to modify a traditional potting mix.
Potting mixes are made by combining organic materials with inorganic materials. The organic matter provides nutrients, while inorganic parts improve drainage and alter the overall texture of the soil. We recommend using peat moss or compost as your organic material for succulents, and perlite, gravel, and a little sand as your inorganic material.
A pot with drainage holes will come in handy to further improve drainage. In addition, your pot material will also play a role in drainage. Pots made from porous materials like concrete, terracotta, or ceramic will retain less water than a glass or metal pot. If you’re a sucker for DIY metal pots and planters, don’t worry– use a drill to create drainage holes in your metal container.
An easy way to avoid overwatering your succulents is to monitor their soil’s moisture content daily and only water when your soil is completely dry. To do so, stick your finger or a moisture meter deep into the pot. When you pull out your finger, it should be dry. For a moisture meter, the meter should read between 1 and 3 to show your soil is dry.
To ensure your succulent is only drinking as much as it needs, consider bottom-watering your succulent. This method involves dipping your succulent into a tub of water and letting it drink for about ten minutes. Then, set the succulent out to dry and drain for a few hours before putting it back in its spot on your windowsill.
If your succulent has edema, there are still several things you can do to help it recover over time. First, let your plant drain if it isn’t. The tips above are excellent for treating edema as well as preventing it. Second, increase the amount of light your succulent receives; they’ll absorb and use water faster in bright, indirect sunlight.
A third way to help treat edema in your succulents is to check your plant’s nutrient levels. Minerals like potassium, magnesium, and calcium are essential for water retention and absorption during photosynthesis. If your succulents aren’t receiving enough nutrients, add some fertilizer or compost to their soil during the growing season to increase nutrient intake.