Shrubs and trees grafted onto an upright stem are very popular in our gardens. They may have different names – I hear “top-grafted”, “standard”, “dwarf standard”, “tree form” and “dwarf tree” – but most are created in the same way. A shrub or small tree, often with a weeping or rounded habit, is grafted onto the top of a single upright stem (called the rootstock) to create the effect of a miniature tree.
Among the most popular top-grafted shrubs are weeping forms of regular shrubs, like weeping peashrub (Caragana arborescens ‘Pendula’ and ‘Walker’), weeping pussywillow (Salix caprea ‘Kilmarnock’ and ‘Pendula’) and weeping mulberry (Morus alba ‘Pendula’). If they grew on their own roots, these mutated forms would simply creep along the ground, but raised on a trunk, they drip down beautifully and become mini-stars!
Among mini-trees with a rounded top – those with a lollypop look to them – you’ll find dwarf Korean lilac (Syringa meyeri ‘Palibin’), dwarf winged euonymus (Euonymus alata ‘Compacta’) and tree roses (various cultivars of Rosa), but there are many, many more.
There are also top-grafted evergreens of all sizes, colors, and shapes.
These “mini-trees” are certainly cute enough, but do have their flaws, including, in many cases, a tendency to sucker at the base. These suckers (new growths sprouting from the roots or the base of the trunk) will not, of course, be the variety you chose: the growths appear from the rootstock, a variety chosen for its straight trunk, not its weeping or bushy habit.
For example, a weeping peashrub is produced by grafting a weeping cultivar (C. arborescens ‘Pendula’ or ‘Walker’) onto the stem of C. arborescens ‘Sutherland’, a cultivar with exceptionally straight stems. If suckers appear at the base of your plant, they therefore will show nothing of the drooping stems of weeping form, but instead the narrow upright branches typical of ‘Sutherland’.
Branches can also appear on the trunk of the weeping tree (if so, they are officially called watersprouts rather than suckers). Since they will be sprouting from below the graft on top of the plant, they too will come from the rootstock, leading to branches that don’t conform to the weeping or dense plant above.
Some top-grafted shrubs are abundant producers of suckers or watersprouts (weeping peashrub and tree roses, for example), others do so only occasionally. Sometimes suckering occurs when the top-graft is dying back for some reason, but other plants will produce suckers or watersprouts even when the top is growing vigorously.
The solution is simple enough: just prune off the unwanted growths! Use pruning shears, cutting as close to the junction point with the grafted tree as possible. If suckers appear from the ground next to the mother plant, you can even remove them with a sharp shovel. There is no particular season for sucker removal: when you see one, just cut if off.
If you fail to remove suckers and watersprouts, they’ll eventually take over and smother your mini-tree (see the photo above), as they are usually faster growing and more dominant than the top-graft. Soon your mini-tree will look nothing like a tree at all. So, if mini-trees are your thing, you may have a bit of pruning to do.