I have a few trees here in Northern Florida, that I will probably be replacing, because they struggle to come out of dormancy and don’t grow well.
I wonder if I should top work them, or replace the whole thing? The graft unions are close to the soil level, so top working would leave at least 6 inches, up to 2 feet of the old variety. I wonder if this would have an effect on chill hour required for the new interstem tree, or other negative effects. For people who have replaced a lot of trees, what are you doing?
An interstem may or may not have an impact on requires chill hours, growth rate, size, or precocity, but if the rootstock and interstem are both healthy and zone-appropriate, I wouldn’t hesitate leave it in unless the original variety is known to have some unfavorable characteristic.
It depends on whether the issues are due to (1) the grafted variety or (2) the rootstock. If the issue is the rootstock, then top-working won’t change anything.
I’ve done a lot of top working for a home gardener. I find WAY more growth on a graft to an established tree than on a graft to a young tree such as you would have with a new purchased tree. So I’d say go with top-working unless there’s some problem with the rootstock.
The established rootstock argument is a strong one. A graft onto a mature root system takes off much faster than a new tree, and you’re not losing all those years of root development. The only time I’d lean toward replacing is if the rootstock itself is the problem, like if it’s poorly adapted to your soil or climate. But if the tree was growing fine before and it’s just the variety you want to change, top working makes more sense.