Is there such thing as a rootstock that instead of limiting a scion's size (a dwarfing rootstock), instead increases the scion's size and vigor (a "giganting" or "maximizing" rootstock)? For example if a standard apple tree grows to 30 feet, but on a dwarfing rootstock grows to 10 feet, is there such thing as a rootstock that could make it 50 feet? Is this theoretically possible (not just for fruit trees, but for any trees)? For example what if I grafted a normally short shrubby juniper on a taller one (like Eastern Redcedar)?
2 Answers
So far as I am aware, no, generally speaking, there are no rootstocks which will make a fruit tree much bigger than the size it would achieve growing on its own roots. It is true, though, that some root stocks used for roses may be used to give more vigour, and 'vigour' may also mean a larger plant than the grafted rose would be growing on its own roots, though 'vigour' more usually means a stronger growing, possibly more disease resistant and more vigorous plant with more blooms than would be possible otherwise, rather than being a much larger plant overall.
Generally, a fruit tree either grows on its own roots, or it is grafted, and one of the reasons for grafting apple trees is to ensure that the tree is a particular variety, since apples do not come true when grown from seed. Growers may also use the grafting technique as an opportunity to create a smaller tree for smaller gardens, and/or to increase disease resistance, but not generally to achieve a much larger tree than the grafted part would normally reach. One of the reasons for that is difficulty in harvesting - there's not much point in having a 50 foot apple tree if you can have one that's 25-30 feet because all those apples have to be harvested, and that's obviously much harder if the tree is very tall.
Further information on rootstocks for fruit trees here https://www.rhs.org.uk/advice/profile?pid=359, though its a UK link. More broadly, see here http://www.hardyfruittrees.ca/tutorials/2014/01/16/why-are-fruit-trees-grafted
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Could this work for ornamental trees at all? For example lets say I have a Blue Point Juniper (J. chinensis), which only reaches 15 feet naturally, grafted on an Eastern Redcedar (J. virginiana) which reaches 50 feet tall.– user27432Nov 13, 2019 at 13:53
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Its a very expert area, rootstocks and grafting- the rootstock has to be compatible with whatever's grafted to it, and its not mature plants which are grafted onto a rootstock, but more usually a bud or a small vegetatively -propagated cutting from the desired tree which then, if successfully grafted, grows on. So I don't know if it would work - you could experiment, but you'd need to get hold of a rootstock as well as creating a bud or propagate a cutting to make the union.– BambooNov 13, 2019 at 16:16
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As @Bamboo mentions there needs to be compatibility between the root-stock and the grafted tree. If the root-stock were a faster growing tree the root-stock would most likely outgrow the grafted tree, once they are no longer in sync the graft would fail. Even if you could get them to grow successfully for a year or more. The trees need to have similar outward growth. A tree with faster outward growth could possibly, be grafted on a slower one, because the top could only grow as fast as the roots can support it, but to do the other way would most likely fail. I think you know what I mean Nov 16, 2019 at 9:06
On the other hand, with cactus, most rootstocks are "giganting" rootstocks. There are generally two purposes for grafting cactus; growing a plant prone to losing it's roots or making the plant growth explode. Most "show" cactus have spent some time on a graft.
The pictured plant is nothing like normal growth. I don't think I've ever heard of using a dwarfing rootstock on cactus. They are generally dwarfy enough.
