I did some testing with winter grafting stonefruit in room temperature this year and would like to share my experience
I grafted Japanese plum scionwood right before Christmas (both scionwood and rootstock were dormant) and kept it in room temperature of about 70-72 degrees.
It took very fast, probably 2 weeks or even less and started to grow very quickly…way faster than outside. Anyway about a week into growing when the shoots were about 5-6 inches it just quit growing. Then I noticed the tip withered and from then on the 5 inches of growth is slowly gradually dying (from the tip). I wasn’t sure if it is the lack of sun or the constant temperature so I took another Japanese plum that I chip budded last May. This one also started to grow rapidly and the shoots are 15 inches long now but they also stayed green and never turned into wood. I have to support them now so they don’t break. They also stalled at growing.
Anyway from what I see the lack of light is not an issue cause the established plum does not have any warning signs and leaves look healthy.
It must be the rapid growth of the graft while it wasn’t still fused with the rootstock that cause it to die eventually. The rootstock was not probably able to nurture the graft completely. It also seems like the lack of cool nights (fluctuating temps) will prevent the plant from forming wood on new growth and the shoots will stay green. My established plum is indoors for about 3 months and the new growth is still green.
I also have few leafed out rootstocks indoors and when I took them out now when we have about 60/45F temps outside, the change in temperature is a big shock, the survival rate is only about 50%.
On the other hand my figs handle indoor temperature fine and my grafted ribes is also doing good.
I wonder how would apples/pears perform. Anyone has similar experience or tips?
I’ve had similar experience with chestnuts (castanea). If they start too quickly and make vigourous growth, they may fail. If the stock plant is not really vigourous and the scion is, the scion may not get enough from the new union to support its growth rate. I sometimes graft into new shoots of a germinating nut, chestnut scions are skinny enough to do that, and if it is a smaller, less robust nut, the graft starts and may fail.
We have wood heat, so temperatures do go down at night after the fire dies, and trees do form woody tissue. You might be on to something
with the lack of wood. I think decreasing hours of light might influence when wood forms too, but I haven’t tried that.
I have an inarch graft right now, of a really vigourous selection, on a so so year old stock. It flushed, the leaf tips browned and the new leaves looked sickly. 3 weeks later, it has just resumed growth and the tiny new bits look good so far. If I get lucky, the scion may root…the free end is in soil.
You can blow up this picture and have a good look. Some of the leaves died and only now are new ones starting. Does this look like your did?
Sounds applicable. But at the same time as soon as scions begin growing/have leaves if they don’t receive enough light they will die.
Your older plum is capable of hanging on with low light, spindly growth. Newly grafted and not enough bright light is an equation for death.
Maybe Jocelyn you’ll find your answer here, too.
Dax
It’s in the same window they were all in last year. Last year only 2 failed.
This year though, I tried an inarch, the free end in soil. That one started quite soon after grafting, perhaps 10 days. Usually they take 19 or 20 days. It’s at 39 days now, and still too soon to say if it will grow.
Dax, I’m not sure how that came out over the internet, grin. Let me try again…I know they need more light, but each batch did survive in that same window for several months. Each year, they lived to be outplanted and made strong trees. There is something else, in addition to low light, this year. I’m not sure about the original posters grafts, because I don’t know if other grafts had that same light exposure and the same time of year. As the sun gets higher in the sky, different windows get more or less direct sun. Mine are all done in February, so the time of year is the same each year. Perhaps the OP will tell us what times of year each graft was made…was there not a difference? Here, it’s still cold, and any grafts need to be inside.
I am in zone 7A and beginning of February is a good time to start grafting if you have a greenhouse where you keep temperature around 37+ degrees.
The plum that died was grafted on the 23rd of December and was kept indoors the whole time.
Second plum was chip budded in May last year and was brought indoors around Jan 10th.
I am attaching picture of both. The first one is pretty much dead for the reasons I mentioned above. It’s not sudden death but it was a gradual process and you can see what state it is now. The second one is doing way better but notice the all green thin shoots. I am curious what will the outside temperature do to it, I am planning to move it outside in about 2-3 weeks. I guess it’s not going to make it once outside but I might be wrong. Some of the green gage rootstocks I moved outside made it and look good.
They’re not indoor plants of course. A greenhouse typically has humid conditions whereas your home is dry air. So, without thinking much about this, it’s the wrong environment.
I’m not going to do much thinking about it.
@jocelyn I’ve not heard of an inarch graft… so I guess I should’ve mentioned that. Now after looking at your picture, I can say I’ve never seen anything like that! What’s its’ purpose? Are roots possible ‘somewhat typically?’ That is wild-looking. 
Dax
Norway maple roots the first year and can be tipped out of the pot to check the amount of roots. Usually it can be cut free then and planted independantly. Apple, cherry and pear are often 2 years to have enough roots. Chestnut, like this one, have about a third of them rooted by the end of the first season, I am told. This is my first chestnut inarch. Starting it in the house gives it several more months to root.
Getting back to Paul’s post. These are just guesses, and you will have to try something different to see if it makes any difference; dormancy at Mid December may not have fully broken, as in, the grafts should have been done later for that reason, they still needed to nap.
Plants are very sensitive to decreasing day length, it signals them strongly to quit growing and to nap, so either later grafting for a time of increasing day length, or light on a timer for increasing days.
The sun moves further south in the sky around early winter, and there may be only a little direct light in the chosen window in Dec, when there could be several hours more of direct light by Feb. There could be a species effect too, as the chestnuts I usually do are shade tolerant.
Have a look at this one from last year, done also in Feb.
pic upload
It is a shade tolerant species, perhaps needing less light than your species.
You are right, I always plant my physalis at the beginning of February and if I don’t keep them right at window they will die pretty soon. They can handle indoor temperatures just fine but they come from Peru so no wonder. Seems like prunus species is not the best adept for this but you don’t know until you try 
Yours looks great, at least you know you can graft your chestnuts in the winter and gain some extra time if needed. Has your green shoot formed any wood yet?
The fig rooted around that time is doing also good as well as the currant so it must be also the genus. Maybe prunus is just more sensitive. I am sure it had nothing to do with dormancy cause the scionwood came from southern hemisphere and it was actually just breaking bud.
The rootstocks (green gage plum) were all doing good and sprouted under the actual graft but stayed green just like the jap. plum.
More humid environment would certainly help but I don’t have a greenhouse so this was the only option.
Well lesson learnt. I will try with apples next year. Judging by Applenut’s pics from Africa I think those could handle the constant temperatures much better.
The chestnut from last year had formed wood by planting time. This year’s graft has stalled and just started up again. I suspect it started too soon before a good union, as it had its free end in the soil and got moisture that way. Then, it stopped, dropped a tiny leaf that was only partly expanded and waited till it got a better union. It will be several more weeks, I suspect, till it gets going again. While I have done other in arch grafts, this is my first chestnut, so I’m just waiting to see what it does
I’m looking at the first plum picture again. There is some green in the stems, can’t tell if there are any new buds at the old leaf axils. Keep it watered and wait a bit, perhaps putting it in a sunnier location/window, if you have one. I don’t think it’s quite dead yet, it won’t hurt to baby it a while and see if it can recover. Do you have a floor lamp you can put a curly florescent bulb into and put it close to the graft for more light?
Just a small update on this topic. The first one obviously did not survive. The 2nd one lost all the leaves while being indoors in ~ the first 10 days of April. I took it outside and let it to it’s fate. Surprisingly it started to sprout around May. I cut one of the 2 branches (see picture above, you can notice the slight bend half way through the stem). It’s growing nicely and will go in ground in couple of days.
