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rootstock overgrowth

Posted by Paul Townsend 
rootstock overgrowth
March 23, 2013 11:47PM
This is what happens when a grafted rootstock was too small for the tree itself ? My only concern is water of course and wind blowing the tree over ... so i keep it pruned way back.

Bayhead Farms
Zone 7a in Washington

Edited 1 time(s). Last edit at 03/24/2013 01:33PM by Michael Phillips.
Re: rootstock overgrowth
March 24, 2013 10:40PM
Over/under growths at the graft union are not signs of incompatability and are common with dwarfing rootstocks. Even with seedling trees, the scion can grow faster than the rootstock. The degree of overgrowth of the scion in your picture is not unusual (it's a bit hard to tell the diameter of the rootstock portion on the left side of the tree, but if it is like that visible on the right, I'd say it was minor, not of particular concern). If the rootstock is one that has a usual recommendation for support (M9, B9, M26 etc) either add a post or keep pruning it to keep it physically small. I have had trees on M26 snap on me after the tail-end of a hurricane came through at harvest (heavy crop), but the support post had snapped, and the tree had snapped below the graft union, not at the union. Judge any support needs based on size of the top of the tree compared with the strength of the stem of the rootstock.

A dwarfing rootstock root system will by its nature be smaller in extent than a seedling rootstock, and the tree may need some extra considerations (extra mulch/weed control, extra irrigation) as far as water. That's just part of the trade-off for its smaller tree size, and is more a function of the extent of root system than the graft union overgrowth.

Jim Gallott
New Haven, VT USDA Zone 5a
Re: rootstock overgrowth
March 26, 2013 06:41PM
If the overgrowth becomes too precarious in future years, support can be achieved through inarch grafting. I have been aiding some weaker and damaged trees here by planting seedlings beside the tree in question and grafting them in with success. I makes little "flying buttresses". Keep in mind this will likely add vigor to the cultivar section, but can greatly add to stability. Looks neat too. As Jim mentioned it is not a sign of trouble necessarily, and I have seen some dramatic examples of overgrowth in some pretty old trees.
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