An ornamental tree that produces sweet, edible fruits, the white mulberry (Morus alba) also tolerates heat and drought well once established and attracts many types of birds. Native to China, this tree generally grows in U.S. Department of Agriculture plant hardiness zones 4 through 8, with slight variation among cultivars. Also suited to growing in a large container, the mulberry thrives in full sun and needs only some basic care and occasional fertilizing to grow well and produce a heavy crop.
The Best Location and Soil
The mulberry tree is a deciduous tree that's about 30 feet tall and wide at maturity. It can grow well in partial sun, but it's growth rate is greatest and its fruit production best when grown in full sun. It also tolerates any type of garden soil that's well-drained, and doesn't do well in soil that's constantly wet or soggy. Increasing the soil's organic content can help boost the tree's growth, so mix several inches of compost into the planting site before setting a young tree in place, and repeat this each spring, spreading about 2 inches of compost under the tree's canopy. Mix the compost into the top inch or two of soil, but do this gently because the mulberry tree tends to have shallow roots than can be damaged easily.
Dwarf mulberry varieties can grow in large containers; for example, the Issai variety (Morus alba 'Issai') is only about 4 feet tall when mature and grows outdoors in USDA zones 5 through 9. It makes a good patio tree, doing best in full sun and planted in any type of commercial potting soil. In colder regions, over-winter the tree indoors, preferably in a west- or south-facing window where light is strong.
Proper Watering and Fertilizing
Insufficient water can cause unripe fruit to fall from a mulberry tree, and it's especially critical for the tree to have evenly moist soil during its first year. Water about once weekly, aiming for at least 1 inch of water every week, including rain. When watering, soak the soil thoroughly, using a soaker hose or drip irrigation to keep foliage dry and prevent fungal growth.
It's also important to fertilize a mulberry tree each year. In warmer parts of its range, feed the tree three times yearly -- in late winter, late spring and late summer -- but in areas with cold temperatures in fall and winter, fertilize only once, in early spring or when you see buds swell and open. Use a 10-10-10 formula that contains trace minerals, mixing 1 cup into the soil under the tree for each year of the tree's life, with a maximum of 9 cups for a mature tree; keep the fertilizer back about 5 inches from the trunk. Don't feed the tree after June in cold-winter areas, or after August in warmer regions, to prevent new growth that's easily damaged by cold.
If you grow a dwarf mulberry in a container, feed it with a balanced, water-soluble fertilizer such as a 20-20-20 formula, diluted at a rate of 1/2 teaspoon per gallon of water, but check your product label for further directions. Fertilize every three or four weeks during the growing season, spring through summer, but withhold fertilizer during winter to give the tree a rest.
A mulberry tree sets fruit on stems that grew late in the previous year -- called old wood -- so it's important to prune at the proper time, to allow fruiting buds to form for the next season's crop. In winter, remove any dead or diseased branches, and take off any branch that crosses and rubs on another branch. You can also prune in spring or early summer to shape the tree or control it's size, but don't take off any branches after mid-summer to allow new fruiting wood to grow. When pruning, disinfect your blades between cuts by wiping them in rubbing alcohol to prevent spreading plant diseases.