Robinia pseudoacacia, also known as the Frisia tree or false acacia, is a quick-growing landscape plant that can reach nearly 7.6 metres (25 feet) in only a few seasons after planting. The tree grows to about 9 metres (30 feet) tall, with a spread reaching out around 4.5 metres (15 feet). If you love the look of the Robinia but prefer to keep it small and contained, pruning is your best option. Pruning this tree can be dangerous, as the wood is thick and brittle and the tree protects itself with sharp thorns. Avoid hurting yourself or damaging the tree when trimming.
Wear thick gardening gloves and a long-sleeved shirt when pruning Robinia pseudoacacia. The thorns will easily tear into skin, so protect your body.
Cut into the Frisia tree using a sharp pruning saw. The sharp saw will make a clean, even cut through the wood. Loppers or shears that are not so sharp or strong will splinter the wood, making it more difficult to control and leaving it open to more danger from infection or insects.
Cut away any damaged or dead branches on the tree. Make the cut at least 15 cm (6 inches) back from the damaged area, or cut a dead branch all the way back to the trunk. This will help prevent the spread of any mould or disease that caused damage to the area.
Prune away any branches that rub together or overcrowd each other. This kind of crowding can lead to mould growth due to lack of air circulation and sunlight penetration into the tree.
Remove any areas of the tree that are reaching too far or too high for your particular tastes. You can control the height and stretch of the tree with regular hard pruning, cutting back as much as half of a branch and a time to slow growth.
Repeat pruning during the growing season if necessary to control the height or spread of the tree. It is especially important to keep track of the growth if the tree grows near your home, near power lines or other such important fixtures, as it grows rapidly and can cause damage if not controlled.
Robinia can withstand pruning nearly any time of year, but respond best if trimming is conducted during the dormant season, generally in late winter or very early spring before the final frost of the year. You can trim again once growth takes place if you notice any areas that need better control or that have been damaged by the winter weather.