The gardener who maintains a parking lot near my home might have fertilized with Prozac. There are a few trees that were weeping cherries when they were installed a few years ago, but they are now not weeping at all! However, it is much more likely that the trees were merely overwhelmed by their own ‘suckers’ because the gardener does not understand grafted trees. What ever happened to the real gardeners?
Of course, those who are not horticultural professionals should not be expected to be proficient with grafting, but might want to recognize and correct minor problems associated with grafting before such problems become serious. Very basically speaking, ‘grafting’ is what brings the understock and scion together as one plant composed of two genetically different parts. ‘Understock’ is what provides the unseen roots that the ‘scion’ is grafted onto. The ‘scion’ is the upper part of the grafted plant that is seen in the garden.
This is done to assemble a plant that exhibits the best qualities of both involved. For example, understock might provide a strong, or more complaisant root system for a tree that would otherwise exhibit an inferior root system. Dwarf citrus are grafted onto a dwarfing rootstock that limits the mature size of the grafted trees that might otherwise become disproportionately large for the garden. Weeping cherries and tree roses are actually grafted twice to assemble an appropriate understock, a mediary stock to provide the strong and straight main trunk and finally, the scion of the desired weeping cherry or hybrid rose.
Suckers are stems that emerge from below the graft and are genetically identical to the understock. Almost all suckers therefore emerge from below the soil or very near to it. However, suckers may also emerge from the mediary stock of weeping cherries, usually immediately below the graft. When the understock realizes that it can divert resources to its own growth, sustaining the scion is not such a priority. Among weeping cherries, the mediary stock naturally grows more aggressively than the scion and has the advantage of extending vertically, consequently shading the pendulous growth of the scion. Suckers among purple leaf plums are likewise advantaged because they have green foliage with more chlorophyll. Removal of suckers as they develop is therefore important to preserve the desired effect.
Variegated plants are mostly genetically unstable and consequently occasionally produce mutant growth known as a ‘sport’ that is not variegated. Although physiologically very different from a sucker, a sport with more chlorophyll may easily overwhelm the desired growth and should likewise be removed as it appears. Sports originate from genetically similar growth and most are merely reversions to growth of superior genetic stability. In fact, most variegated cultivars originated as variegated sports among normally un-variegated plants. The most common species that may produce green sports from variegated cultivars include English holly, Algerian ivy, Pittosporumtobira, Euonymus, daphne and pieris (lily of the valley shrub).
Ask Tony Tomeo a gardening question at www.AskTonyTheGardener.com