Curious Effect of Heat on Apples

Another curious effect of that stint of 113F heat we had a couple weeks ago is that my higher-chill trees that were still stubbornly dormant are leafing out and blossoming now. Empire, Honeycrisp, Black Oxford, Red Boskoop, and Lurared are all blossoming nicely in a tight little group together, and setting fruit. If they can make it through the summer, they will be ripening in our December weather, which is warm, clear sunny days and frosty nights a little above freezing (which is what makes our citrus so good).

Not sure if this breaking dormancy has to do with just delayed blossoming, or the heat actually triggers something. I’m leaning towards the latter, as I sort of suspected this in the past when the same thing happened in late April when we had a nasty bit of early heat. Maybe the heat shocks the tree into thinking it has survived trauma like a harsh winter (note the crispy leaf singed from the heat) and now its time to perk up.


High heat does replace lack of chilling to some degree. I had a link at one time but it no longer seems to work.

Our delay in blooming is less than yours because we get more chilling but it can still be a couple of months

1 Like

I can’t add too much, but to say I may have something to add this time next year. The weather has been consistent and apparently will continue being so.

1 Like

I’m glad this hasn’t been a year where we’ve been hitting 113. The last time we did that our heat index was in the 130’s. Low 100’s is more than enough for me.

I wish your honeycrisp would talk to mine and tell it to get out of bed. I’ve been tempted to try pruning off the ends of its branches to see if that would stimulate it. Honeycrisp only had a couple of branches on one side reluctantly and partially kick in this year, and those were very late. Bevin’s Favorite bloomed a second time and Ichi Ki Kei Jiro persimmon decided to start pushing out a lot of new growth in areas where it didn’t leaf out this spring, as well as new tip growth.

I usually have little to no new growth on most trees, especially apples, during summer. This year many of the apples reminded me of your African apple pics in that they only leafed out near the tips. I do suspect that the alleviation of both winter chill and excessive heat stress could kick off similar hormonal responses, but you guys have a lot more experience and understanding of how apple trees function in different conditions.

It takes a few years for the tree to figure out where its at. Oddly enough, they seem to have less trouble with it in Uganda than I do here. Many are just slow starters, Fuji being one of the worst. It will struggle along for 4-5 years, and right when you’re fed up and ready to pull it out, something kicks in and then it’s one of the most compact blooms and reliable bearers in the orchard. Painting the tree white is mandatory, as it may be bare of leaves through some pretty nasty heat, which would cook any unprotected bark.

1 Like

That sounds like the description of my Red Fuji. Fourth year it bloomed and held a few apples. It also grew very well that year. Fifth year it outshines everything else.

The limbs of HC that I grafted on less vigorous rootstock have been slow to come out of dormancy. Last years grafts HC to my standard pear (via interstem) started out slow but have considerable new growth. Sure hoping to get some blooms/apples off it in 2017.

I’m not entirely sure the amount of heat required to break dormancy. We get a lot of dry heat around 105 early on that doesn’t seem to do much. It’s only after spikes of 106+ that I see some leaf singeing and resultant blossoming. I guess it needs enough heat to hurt the tree a little bit to break dormancy and start flowering.

Yup. My Red Fuji is on year 5, and loaded with fruit this year for the first time. And, my regular Fuji, too.

Thin them hard, one per cluster, a hand’s spread between fruits. Fuji tends to have bunches of tiny apples on branch tips that never size up correctly unless thinned hard. The ones off your tree will absolutely blow your mind compared to the ones from the store, much more cinnamon and spice to them.

1 Like

I removed at least 80% early on, and then more later. I probably still left more than I should have.

Wow! Thank you for post. I had thought my HC grafts from last year were gonners. No, just late starters.

I have thinned, but need to thin, again, as that is the exact description for both my Fujis. And yes - they blew my mind 2 seasons ago. I have never, ever had an apple so good in all my life. I think I ate all of the apples off my Fujis. Didn’t leave any for my poor dh. Only had a few that season, but this year, we’ve got a bumper crop. They were beyond outstanding. So good, I bought 2 more Fuji varieties.

1 Like

My Anna and Tropical Sweet are now setting fruit as we are now half way through our Southern Hemisphere spring. This is their second spring and they have been going gangbusters.

I stripped the leaves from my granny smith and my royal gala in early August and the granny smith is just starting to break dormancy now with what is the first green starting to show along a branch over the past few days. The royal gala is not far away from showing its hand. They are both in their first season in our sub tropic climate where we get about 200 chill hours and where our day temperature is now around 30c. so I am looking forward to seeing if they bear fruit.

So with some trees still to break dormancy and others still to wake I am inclined to agree that days where the earth is warming is needed to assist with the breaking of dormancy.


1 Like

Well, it happened again; after a relatively mild (mid 90’s) early summer, we were hit with some ssssssssmokin’ hot days (115F). The effect was like when you easterners get a really cold snap during a mild Indian summer; it burned the outside leaves of even our big persimmon tree and absolutely incinerated about 50 rose bushes. Last year’s mild winter had left a lot of blind wood on the apple trees, and now these dormant buds are popping.

We had a second round of 110F but it didn’t do nearly the damage as the first round; it’s like the plants were hardened off.