Showy mountain ashes are sensitive to drought and heat. Therefore, it is important that they receive about an inch of water a week from rainfall or from a hose or drip irrigation system. Adequate moisture is especially important during the first few months after planting. Regular watering during hot summers is essential to cool the soil and provide sufficient moisture to maintain tree vigor. Run a sprinkler or drip system from to 30 minutes every week or 10 days during periods of high heat and sparse rainfall. Spread a layer of mulch under the tree to retard evaporation of moisture from the soil.
For more information see file on Caring for Trees.
Mountain ashes are not heavy feeders. They can survive nicely on minimal nutrition. However, it is a good idea to feed mountain ashes in the yard once a year. In the spring sprinkle a handful or two of a fertilizer on the soil under the tree out as far as the reach of its branches (the drip line). The rain will soak it in.
For more information see file on Choosing Fertilizers.
A 2 to 3 inch layer of some attractive organic material spread on the soil under mountain ash trees provides many benefits. Wood chips, chopped leaves, shredded bark or similar materials, laid directly on the soil or over landscape fabric spread on the soil first, will inhibit weeds and water evaporation from the soil. This mulch will also protect the tree trunk from damage from mechanical yard care equipment.
For more information see file on Using Mulch
Mountain ashes do not require routine pruning. Occasionally it may be necessary to cut out a damaged or diseased branch, or to shape the tree somewhat. Do any pruning while the tree is dormant, around February.
For more information see files on Pruning Trees and Choosing Pruning Tools