I have been trying to topwork grapes for several years (grafting dormant scion onto the plants in spring) without much luck. I think I finally found a method that works. Here is a summary.

• Graft before several days of hot weather, above 80F. The earlier the better otherwise. We had an early heat wave in early May and that is when I grafted. Grapes callous fastest at about 85-90F.

• Many types of graft can work but I find the cleft graft is the best due to the tight holding of the scion.

• Graft low on the main stem.

• Wrap the graft well with tape or parafilm. Cover it completely. I use parafilm and put 5-6 layers on.

• Paint over the entire thing (scions, graft area, all taped area plus a bit below it) thoroughly with Doc Farewells or similar. A main purpose here is to form a complete "cap" seal over the whole graft to prevent sap from leaking out through the graft. Grafts leaking sap tend not to callous. You need to have a complete seal so blob on tons of paint.

• Cut several 1/4" deep gashes in the stock below the grafts, to allow sap to escape. Check them every few days to make sure they are still "flowing" and if not, cut them again.
  

Now what you should have is a graft which will not have any sap flowing through it due to the combination of the cuts below and the cap on top. I did one graft without much parafilm and found the paint alone was not enough to make a good seal (I think there was so much sap flowing that it did not harden everywhere and one leak ruins it all). That graft is the only one that is not sprouting now.

I am also trying a couple green grafts - when my this years shoots got 1' long I cut some and removed the leaves and grafted the shoots to existing cut-off trunks. I put baggies over the top to keep them from drying out. This was about a week ago and none have died off so maybe some of them will make it. Usually the recommendation for green grafts is to wait until later to do them, but I did not have luck in the past so thought I would try some early ones.

The earlier dormant wood grafts are sprouting well now, but I have known from the past that they can sometimes sprout even when the graft eventually fails. But, the growth seems strong enough that I expect most will work.

Scott