Brown Spots on Outdoor Bamboo Plants
At the meditation center I help run, the leaves of three of our large, potted, outdoor bamboo plants are covered in brown spots. I'm thinking this isn't good, but my attempts to search on the web have come up empty. Could you provide any information on cause and, if it's a problem, the remedy??
Multnomah County Oregon
Your bamboo is probably pot-bound, especially if it has been in the pot for more than a couple of years. Bamboo should be divided and repotted every 3-5 years as the plant grows. The soil needs to be replaced and the roots given more space. Bamboo are generally vigorous plants, but require a little more care if in pots. Bamboo in pots are more sensitive to heat, especially if in a black pot. Bamboo in pots need to be watered 3-5 times per week, more in hot, dry weather. This is because the roots are limited to just the soil of the pot. It's also important to be sure the pot is draining correctly so water comes out the bottom when you water. To function properly plant roots require aeration. If pores in the soil are full of water, air cannot get to the roots.
The primary cause of yellowing leaves is the normal leaf drop of older leaves. Bamboo are perennial plants that shed their leaves gradually over the year with the oldest leaves turning yellow and dropping. If the cause is normal leaf shedding most of the leaves on the bamboo should be green and healthy looking. Often bamboo will shed leaves more heavily in the spring. Other causes for leaf yellowing and brown areas include overwatering or poor drainage resulting in water-logged soil that doesn't "breathe" or allow oxygen down into the roots. The solution is either to water less frequently, giving the soil a chance to drain, opening spaces for air to infiltrate. This article had good information on Growing and Maintaining Bamboo http://bamboogarden.com/care.htm, including a discussion of bamboo in pots.Most species of bamboo prefer full sun, though some varieties prefer dappled shade. Bamboo also prefer fertile, well-drained soil that is kept moist, but not wet. Leaving shed leaves over the root system, even in pots provides a natural mulch system. Adding additional 2-4 inches of wood chip, shredded bark or compost mulch helps keep soil moisture consistent by decreasing soil evaporation. Mulch also helps moderate soil temperatures and keeps down the weeds that compete for water and nutrients. Over time mulch will add organic matter to the soil as it breaks do