Succulents are plants with leaves or stems that store water. They usually have thickened leaves and may or may not have spines. Cactus are succulents as are plants like the common aloe and sedum. Most are frost tender and require bright sun and warm temperatures. Succulents are commonly grown in pots with a variety of the plants. Most problems arise in succulents with improper care or siting but there are also many diseases and pests that trouble succulents.
Succulents need to be in a bright sunny area to thrive. While we usually think of succulents as desert dwellers that need little water, this is not always the case. What they do need is well drained soil with a gritty composition. Any container grown plants need a pot with holes to encourage drainage. Over watered plants can get Succulents grow in low nutrient areas and rarely need fertilizing until they have their first spring growth. Over fertilizing will cause the plants to get yellow foliage and leaf or spine drop. Fertilizer carries sodium which is toxic to plants in high doses. In cases of fertilizer burn the roots can become damaged which results in foliage drop or drooping. During the fertilizing season water until the pot leaches moisture to help prevent sodium build up. Then allow the pot to dry out before you irrigate again. Temperature can also cause damage to the plant. Succulents that experience freezing temperatures will often thaw out but become mushy and finally the foliage will darken and probably die.
Succulents should be in full sun but searing pinpoint light can cause sun scorch or scald. This causes discolored leaves that turn silver or white or the entire plant may bleach or turn orange. In extremely hot climates a succulent should have dappled light during the high heat of the day. Succulents grown in southern facing windows will benefit from some shelter at the time of day the sun is highest. The light becomes like a magnifying glass focused on an ant and will burn the tender plants. A succulent that receives too little light will get leggy as it stretches for sun.
Mealy bugs, scale, fungus gnats and spider mites are the primary pests of succulents. Fungus gnats are annoying but really don't cause damage. They are best controlled by using dry cactus soils and not over watering. Spider mites leave tiny webbing on the plant and cause yellow spots on the foliage which darkens to rusty brown. Scale are sucking insects that reduce the general vigor of the plant and excrete honeydew, which is a sticky substance that builds up on leaves and may turn into sooty mold. Mealy bugs abound on cactus and may attack foliage, stems or roots. The plant will look generally sick and may even rot away if infestation is severe. Other pests such as leaf miners leave trails in the leaves or stems.
Fungal diseases are the most common problems in succulents. Fungus blooms in warm, moist conditions and can take numerous forms and cause a variety of damage. Boytris and Phytophtora are usual culprits. They cause the stem to soften and eventually collapse. Sooty mold can make leaves fall off and a disease called Basal Stem Rot will see the entire stem turn black or red and rot at the soil level. Aloe rust affects a few succulents such as aloe where the foliage gets black spots. This is caused by overhead watering and while unsightly, will do no permanent damage.