Robinia pseudoacacia 'UMBRACULIFERA' mop-head acacia, black locust
size/type
small tree,small tree
usual height
3-5m
usual width
2-4m
leaves
deciduous broadleaf
colour of leaves
flowers
insignificant or non-blooming
location
full to partial sun
soil type
any (acidic to alkaline)
soil moisture requirements
evenly moist but well-drained
USDA zone (lowest)
4 (down to -34°C)
winter protection
for zone 5+6
for zone 7
categorized
Black locust comes from Mexico and North America where it grows vigorously owing to invasive runners, spreading in unmaintained areas. This also happens in our country, which is why you can often see its beautiful, bright green foliage for example along railways, usually in dry soil and full sun. Fortunately, cultivated varieties usually lack invasive potential, so they are safe for gardens where they prove to be reliable in our C.E. conditions. Being virtually maintenance-free, they are popular in public greenery, too.
Description of the plant:
Umbraculifera is a dwarf variety of black locust that originated in Austria in 1813. It makes deciduous, 25-30 cm long, pinnate leaves, composed of up to 23 elliptical or oval leaflets. They emerge light green and mature to a slightly darker shade of green, but never too dark. And since black locust lacks a gene common to most other native deciduous trees that tells them to stop growing at the end of the season, black locusts keep producing new leaves until the autumn. Therefore, their canopies are constantly a combination of darker, mature leaves and young, bright green leaves. Another plus is that they last exceptionally long. In warm, urban environment they remain on the trees often into December and fall off only after the arrival of really strong frosts.Umbraculifera belongs among top five favourites suitable for small gardens and narrow streets as it has a compact, spherical crown that commonly grows to between 2 and 4 meters in width and slightly less in height. Only in open ground with unlimited root space they get slightly larger. Another advantage is the fact that it doesn't bloom, so don't expect a pile of withered, rotting flowers down on the ground as you can see under common, white-flowered locust. Standard trees always need a strong support for the first 3 years after planting before they establish. Also, during that time don't let the lawn grow close to the trunk – keep the area above roots clean and ideally mulched.
Locusts are not fussy about soil type, they even tolerate road salt but can’t cope with boggy or wet ground. They do not suffer from pests or common diseases, but we have seen trees with dead parts of the crown, most likely caused by a fungal disease hidden in the wood. The compact shape of the crown is natural without pruning, yet it can be done in early spring if you want to keep the crown size smaller. Fertilizing makes no sense. Fully hardy to min. -34 °C (USDA one 4).
Last update 07-12-2008; 24-01-2024
