It is not the roots that require the chilling. I would go ahead and graft the low chill varieties onto your stock. Too late this year to get dormant low chill scions, probably. Next year you can get scions from your neighbors and graft over maybe a third of each of your trees. In three years you will have them all done. Al

Thanks, calistoga.

Two more questions to ponder:

1) If it isn't the roots that determine chilling hours, then how come budbreak in my late chill varieties are so far behind my low chill varieties? Don't the roots pump up the water and nutrients in spring to get the buds to break and leaves to appear? I'd always assumed that the late chill varieties were late because this pumping process is delayed in late chill varieties. Not true? What DOES determine the lateness or earliness of a variety? What part of the plant recognizes daylength/temperature? Clearly this is a genetic mechanism, however complicated. What would happen if you kept the roots cold but let the tops warm up? Or vice versa? Dang, I guess I really have no clue how the plant determines chilling hours.

2) I collected dormant wood in January, and kept it in the fridge wrapped in wet newspaper, so we should be ready to go this year for grafting--that is, unless we decide to just replace the trees. Would something bad happen if we grafted more than 1/3 of the tree this first year? Like we'd weaken the tree?

Thanks, Thisbud4U

It's the flower and leaf buds that recognize/need chilling. Getting them chilled controls the fruiting and leafing of the tree, not the roots. You will do fine using what you have as a rootstock. After all those trees have survived and grown, just not fruited. You can graft over the entire tree this yr. But you might leave one nurse limb on each tree until the grafts take over. If some of your grafts fail, hopefully vigorous sprouts will arise below the grafting cuts. You can T bud those sprouts later in the summer and force them next spring.

If you aren't sure of your grafting skills, then you might want to spread the grafting over 2-3 years.

The Fruitnut

Many thanks, Fruitnut.

If your scion wood kept in the wet newspaper did not dry out in the refrigerator(I keep mine in a plastic ziplock to be sure)it should still be in good condition and dormant. Al

I'm close to the same area. Generally only two kinds of apricots are sold in the southern part of the state: Blenheim (also called 'Royal Apricot') and Goldkist. (Katy is another ultra-low chill variety that has recently started becoming available)

Blenheim is by far the popular commercial variety in California, but it is not truly a low-chill variety. It might be able to do okay in Santa Cruz but south of that it is not going to be able to produce fruit consistently, not unless it is up at a higher elevation that gets more winter chill. I have heard of people in certain parts of Orange County being able to get somewhat satisfactory crops from Blenheim, but in San Diego you would be out of luck! Maybe in Vista.

So my guess would be that your "high-chill" apricots that were planted are probably Blenheim. Blenheim is more of a 'low to medium' chill apricot. It grows best with 400 chill hours, can produce with less under ideal conditions, if there are no warm winter days, and at 200 chill hours it will have substantially diminished fruit yield and might only produce fruit every other year. I'm almost sure your apricots are Blenheim, Blenheim was the popular apricot variety in Southern California, it was just never ideally adapted to the climate, and certainly not all the way down south in San Diego.

I have an apricot tree, where the upper part of the tree gets full sun and the lower part of the tree is mostly shaded by a wall, and it really seems the upper and lower parts of the tree are on two different cycles. The leaves on the upper part of the tree last much longer, while all the lower leaves fall off. The leaves on the upper part of the tree did not begin falling off until January. Then when it comes time for regrowth, the leaves on the bottom are the first to appear, because the bottom half of the tree has been in dormancy longer. The difference in timing is out of synch by about 6 weeks. It really seemed like exposure to sunlight had a big part to play.

From my experience, it seems like coming out of dormancy is more influenced by localized influences on a certain part of the tree, rather than some sort of hormone levels circulating throughout the tree. So I would think that grafting low-chill apricots onto higher chill rootstock should work just fine. Once the buds break from outside environmental influence, then they send out hormones that later stimulate the rest of the tree.

Not only this, but I think apricots are usually grafted anyway, so whether you buy Blenheim or Goldkist, it will likely be on the same variety rootstock (whatever that is).

If anyone in SoCal already has older cherry trees (i.e. Bing) growing on their property, and they have never been productive, one option could be to graft the new low-chill varieties onto them.