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There is a common problem with fruit trees in temperate climates where the trees flower before the last frost. Generally speaking, if the tree has flowered, and the temperature drops below freezing, the flowers die and do not produce fruit.

This is certainly not a new problem. It's my understanding that the problem affects almost the entire fruit farming industry in temperate climates.

I've heard that fruit farmers have large-scale commercial techniques that they use to mitigate the issue, such as:

  • Covering
  • Fog or smoke
  • Wind Machines
  • Sprinkling
  • Heating

While these methods might be practical for commercial farmers, not all of them are practical for small-scale urban farmers like me.

Instead of actively protecting the open flowers, would it be possible to trick fruit trees into not flowering as early?

I'm dealing specifically with plants in the prunus genus:

Examples:

  • Prunus tomentosa
  • Prunus besseyi x prunus salicina hybrids
  • Prunus avium x prunus salicina hybrids

Note: I have a related question here: What triggers plants in the prunus genus to flower?

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  • $\begingroup$ Unfortunately, your assumption ("I'm making an assumption that trees don't flower when the ground is frozen") is incorrect, which makes both the question and the current answer a little bit meaningless. Plants don't rely on temperature (ground or air) to set the time to flower. They measure the length of the night, which varies according to the seasons. Also, it's worth mentioning (unfortunately, again) that on SE sites you cannot receive your bounty back. As this question has no answer (because it's based on a wrong assumption), you lost your points for nothing. $\endgroup$
    – user24284
    Jan 2, 2018 at 8:29
  • $\begingroup$ @GerardoFurtado : So, does this mean that a plant would flower on the exact same day, every single year? No other factors influence bloom time? $\endgroup$
    – User1974
    Jan 2, 2018 at 16:30
  • $\begingroup$ Not the same day, but very close. Other factors do have influence, I'm just saying that the main factor is the photoperiod, not temperature. $\endgroup$
    – user24284
    Jan 2, 2018 at 21:48
  • $\begingroup$ @GerardoFurtad: no, temperature on root is the main factor on common fruit plants (e.g. in many Rosaceae, where flowers appears before leaves). E.g. Prunus armeniaca (apricot) should be planted on colder places, to make them flower later (such plants hate cold weather during flowering). I live in a mountaneous region, and I can tell you that leaves (or flowers) on wild tree are phased out according altitude (same latitude, so same light period). Just few perennial plants in botanical gardens use the light period. $\endgroup$
    – Giacomo Catenazzi
    Jan 3, 2018 at 10:21
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    $\begingroup$ @Wilson Good. That's a specific question, better than this one to discuss that subject, so you can get proper answers explaining photoperiodism and the effect of vernalization on the floral evocation. $\endgroup$
    – user24284
    Jan 3, 2018 at 14:45

2 Answers 2

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The Principles of Fruit-Growing By Liberty Bailey 1898 (from page 92):

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  • $\begingroup$ Thanks for this answer. Definitely contradicts my answer. More research needed. $\endgroup$
    – Sherwood Botsford
    Jan 3, 2018 at 0:42
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You are on the right track, but snow is the wrong way. When the snow is around it insulates the ground. Soil surface temps stabilize at close to freezing.

Instead, do the reverse. Remove, or firmly pack the snow. Do so about 1.5 times the dripline radius. (If the dripline is 10 feet from the trunk, pack out to 15.)

This allows the ground to freeze deeper. However see other answers. I'm not nearly as confident about this now.

Now once melt starts in earnest, cover the ground with a couple of layers of the insulated tarps used by contractors to pour concrete in freezing conditions. This will keep the ground cold, both by reflection (most tarps of white) and by insulation, and by wind reduction. This should slowdown bud break by at least a week, and more likely two weeks.

For a single tree, you may be able to do protection with an oscillating sprinkler (for a big tree) or a impact rotary. Key thing with these is to start them before the temperature gets down to freezing. The initial few minutes while it's working with dry air you can get supercooled droplets that kill your buds instantly. Start the sprinkler when the temps are about +6

A third way that may help is to graft onto a different root stock. The russians work with pear on cotoneaster. This dwarfs the pear strongly, but also forces it into dormancy earlier. I haven't read what it does to bud break, but given that pears also tend to be early bloomers, it must help. These interspecies grafts are working in Siberia in zone 2.

Look at using prunus that tend to go into dormancy early in the fall.

Another way to experiment with would be to keep them a bit thirsty in the fall. If the roots are slightly dehydrated, then the first moisture they get in spring will be used to rehydrate. This may delay bud break by a day or two.

Some trees do their budding on reserves in the bud and twig itself. I see this some years when a winter has killed roots. The leaves break bud, inflate about to about 1/4 size, then wither. For these guys it's a matter of enough degree days or the day length on the bud itself.

If it's degree days, you may be able to stretch things out by making the tree lighter coloured. Many people spray dormant oil in late winter anyway. By adding some cheap latex paint to the dormant oil mix, you lighten the colour of the twig, and so reduce sun warming.

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