The Japanese aralia (Fatsia japonica) is a 5- to 12-foot shrub serving both as a landscape ornamental and a houseplant. In nature they are found in wooded areas and thickets. Cultivated Japanese aralias are hardy to USDA Plant Hardiness zones 8 to 10 Japanese aralia is a late bloomer, producing white starbursts of flowers in the fall. Discolored foliage is a common problem with this shrub, stemming from a number of possible causes.
The Japanese aralia thrives in temperatures below 70 degrees Fahrenheit during the growing season and below 60 degrees Fahrenheit in winter. If the aralia is grown indoors, provide it with a bright spot out of direct sun. The outdoor-grown aralia needs afternoon shade. In winter, place it under grow lights if there is a lack of sunshine. If the leaves turn yellow and shrivel, the plant is getting too much direct sun.
Overwatering kills more plants than anything else, according to the Clark County Master Gardeners. The Japanese aralia requires consistent watering during the growing period and a decrease in both the frequency and amount of water in the winter. If the yellow leaves are soft and wilted, overwatering may be the cause. Allow the plant to dry out almost completely before watering, then begin keeping the soil evenly moist. It should have the moisture content of a wrung-out sponge. If the yellow leaves have brown, crispy edges, the aralia may not be getting enough water. Add a little more water at each irrigation until the plant responds.
The Japanese aralia requires fertilizer once a month while in active growth to produce deep, green foliage and strong stems. A lack of nitrogen--represented by the first number in the fertilizer formula--will cause yellow leaves. Check your fertilizer label; if the first number is lower than the others, purchase a balanced fertilizer such as 10-10-10. Apply the fertilizer monthly during the growing season at the rate listed on the package for your aralia's size and age.
Micronutrients and Soil pH
Mention yellow foliage to most master gardeners, and you will immediately receive a possible diagnoses: chlorosis. The yellowing is caused by a lack of chlorophyll, due to inadequate soil drainage, damaged or compacted roots, alkaline soil or nutrient deficiencies. Japanese aralia requires iron, manganese and zinc to keep its foliage green. Yellowing of young leaves is an indication of an iron deficiency. Manganese or zinc is lacking if the inner and older leaves turn yellow. Consult with your county extension agent about how to adjust the soil's pH and which soil drenches to use to correct any nutrient deficiencies.