Aeonium arboreum 'Zwartkop', commonly called Black Rose, is an ornamental succulent grown for its purplish-black foliage, which is arranged in a rosette shape. It grows outdoors in U.S. Department of Agriculture plant hardiness zones 9 through 11, where it adds year-round visual interest to garden beds. Although typically problem-free, Black Rose plants may sometimes drop leaves. Most causes are temporary or avoidable, although some may indicate a serious issue that must be addressed to save the plant's life.
Black Rose plants grow actively in spring and early summer and from fall into early winter. They enter dormancy as summer temperatures climb, dropping their foliage rosettes to direct energy toward their stems, or growing tips, and roots. Fall rain revives the plants until colder temperatures set in and prompt a second, less profound dormancy period in winter. Leaf loss from seasonal dormancy is temporary and natural and is not accompanied by other worrying symptoms such as wilting, discoloration or stem dieback. You don't need to do anything except wait and water the plant occasionally so the stem doesn't dry out.
Cultural problems can cause massive damage to Black Rose plants, including leaf loss. Soggy soil and over-watering are perhaps the most common and serious cultural issues for Black Rose plants because too much water will drown the roots and may lead to root rot, particularly during cold weather. Temperatures below 20 degrees Fahrenheit will also badly damage the leaf tips and may cause foliage loss. Conversely, direct sun exposure and temperatures above 100 F will also cause foliage loss and damage, particularly if the soil is too dry. Growing Black Rose plants in a fast-draining bed with light afternoon shade in hot, dry inland areas will help limit stress-related leaf loss, as will providing cover during cold or frosty weather.
Root rot strikes when Black Rose plants are in cold, wet soil. It causes mushy, blackened stems and a general decline in the plant's appearance and vigor, as well as leaf drop. Little can be done to help Black Rose plants afflicted with root rot, so prevention is key. Plant them in a bed or pot with gritty, fast-draining soil and provide adequate sun exposure to help keep the soil warm and dry. If symptoms of root rot appear, such as soft spots on the stem or minor leaf loss, stop all watering for several weeks to see if the problem will correct itself. If the symptoms persist and worsen, the plant may need to be replaced.
Serious infestations of mealybugs and spider mites may cause foliage loss in Black Rose plants, although it is rare in healthy, unstressed plants. Accompanying symptoms include discolored leaves, stem dieback and sticky or cottony reside between the leaves. Infestations of either type of pest can be treated with a liberal application of ready-to-use insecticidal soap applied to the tops and undersides of the leaves at seven- to 10-day intervals. Proper care will help prevent serious pest infestations in Black Rose plants, as will planting them in a bug-free site away from areas where infestations have previously occurred.
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