Grafted apple: when to cut off growth from stock

[bertiefox]

Having grown a lot of malus baccata or Siberian crabs, from seed, I decided to try grafting a favourite late apple on to a number of them this year. They are already well established little bushes and some have started flowering, as they have been in place for about five years or so.
The grafts have taken on two of them, and on one of them I've cut back all the growth leaving two main stems from near the ground, one still growing as the crab, the other as the desired variety.
I wondered if there would be any disadvantage to growing this on as a 'dual tree' with the crab flowers on one main stem, and the fruiting variety on the other? Or would this tend to weaken the fruit production or drain energy from the graft?
If I am to cut back the stem which is the rootstock, when do I do this? Should I do it immediately, which would leave very few leaves on the tree, or should I delay until winter pruning?

[wildseed57]

I don't see any disadvantage other than reducing the amount of production some, often in orchards they will have a flowering crab tree to help increase the amount of pollen that the trees can get some varieties are self sterile or partially self pollinating and need other varieties to pollinate them. So long as you remove the flowers from the grafted stock for the first two years the graft should be strong enough to produce apples on its own unless its still weak and needs another year for the graft to completely take over.
George W.

[bertiefox]

Thanks for the advice. I expect I wouldn't have thought to remove the flowers, so thanks for that good advice. The variety I am reproducing is a local one called simply Delbard tardive, and well worth the effort.