Native to Central America, tree dahlias are popular flowering plants that can reach heights of 30 feet. Unlike the smaller species of dahlias, you can plant dahlias in the back of flowerbeds behind shorter plants. In addition, there is a wide range of blossom colours you can choose from, such as pink, lavender and white.
Lift your tree dahlia from its container and plant in a 1- to 2-gallon pot filled with potting soil. The potting soil should reach to within 1 1/2 inches of the top of the pot.
Set your pot on a saucer filled with a 1-inch layer of pea gravel. Water the tree dahlia to moisten the soil. Place your tree dahlia in an area that receives filtered sunlight. Keep the tree in this location for one week. Move the pot to a location that receives an hour of direct sun. Continue to introduce it to more light every four days until it is kept in a full sun area or a location that receives six to eight hours of sun.
Dig a 6-inch hole in a location that has well draining soil. Collect dirt from the bottom of this hole to conduct a soil pH test. Tree dahlias need a pH range between 6.1 to 6.5 to absorb the soil's nutrients. Conduct a soil pH test according to the directions on the label. Based on the results, spread lime to soil that is under 6.1 and sulphur to soil that is over 6.5.
Make a hole that is twice as wide as the plant's root ball and at the same depth as the tree dahlia was planted in the container. Place the plant inside of the hole and pack soil around the base to reduce any air pockets. Water the soil. Spread a 3-inch layer of mulch from 3 inches from the base to the plant's drip line, or the area underneath the plant's outermost edges.
Fertilise your tree dahlia with a vegetable fertiliser. Dilute the fertiliser according to the package and apply underneath the drip line of the plant. Water the plant thoroughly.
Prune your tree dahlia with a pair of bypass shears in the late winter. New shoots should be reduced to 1/3 or 1/2 of their length. Make 45-degree angled cuts into the shoots.
Keep your newly planted tree dahlia watered to prevent the root ball from drying out.
Monitor your tree dahlia for aphids, slugs, leaf-miners and spider mites. Hand-pick or spray off the bugs with a stream of water.