How and why trees are grafted, and what can go wrong

DEAR JESSICA: After superstorm Sandy, we transplanted a dwarf Japanese split-leaf red maple tree. The leaves on the tree are now green, and some of the leaves reverted to a full leaf. Is there anything we can do to have it revert to a red split leaf? — Rick Partenza, Dix Hills

DEAR RICK: Too much sun exposure can alter the color of red-leaf maple trees, which require a bit of protection to maintain foliage color. Too much or too little water also can cause leaf fading.

If you only were reporting a change in color and had transplanted the tree to an area with less shade, we’d have our answer, and you’d likely just have to provide some shade by planting a larger-growing tree nearby or adjusting watering and/or drainage. But because the leaf type on your tree also has changed from split-leaf to full-leaf, this indicates your tree was grafted and has reverted to the original rootstock.

Grafting is a method of hybridizing that introduces the desired qualities of one plant or tree into another — usually stronger-rooted — plant or tree. Japanese maples are typically grafted because growing them from seed does not result in consistent qualities. Grafting, on the other hand, creates an identical offspring.

In grafting, a cut is made in the wood of a tree, which is called the rootstock, and a branch from a different tree, called the scion, is attached to it. Rootstock wood from above the scion is then removed so that when the parts heal together, the scion takes over the top of the tree, and its branches, habit, leaf and flower type and color, etc., take over. In your case, the rootstock was a full, green-leaved species, most likely Acer palmatum.

In grafting, as in life, however, things sometimes go wrong. Sometimes the scion is rejected, and the tree reverts to the qualities of the rootstock. Sometimes the scion just dies, and the rootstock takes over. Sometimes only half the tree reverts, depending on where the tree was grafted and how well it subsequently grew.

In addition, hard pruning of grafted trees can stimulate sprouting of the original rootstock from the base of the tree, and this growth will have the qualities of the rootstock.

It’s also possible that the root system was cut when the tree was removed from its original location, and that the remaining roots were inadequate to support the grafted tree.

Your photo indicates the majority of your tree has reverted, so pruning away branches from rootstock growth does not appear to be an option. I’m sorry, but there really isn’t anything you can do.

DEAR JESSICA: I was wondering if you had any experience with hydrangeas, and why they might not bloom. I have several varieties (all very healthy plants) that make beautiful foliage but never flower. I purchased a few from nurseries — including a climbing version — and the others were grown from clippings. I have Googled to no avail, and rather than pulling them out of the ground I thought I would ask an expert. — Susan Sineo, Manorville

DEAR SUSAN: There are a few possibilities. If you’re fertilizing your hydrangeas — or if they are near a lawn that is fertilized — too much nitrogen could be resulting in flowerless plants. Improper pruning also is problematic. If pruning is done at the wrong time of year, buds that would become flowers are inadvertently removed. (Here’s my pruning guide for different hydrangea species: newsday.com/hydrangeas)

The severe cold the past two winters also could be to blame, as could too much or too little sun.

Also, pertaining to the plants you grew from clippings, a few years could pass before plants are mature enough to flower.

Hope this helps!