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Fruit tree critical temperatures

Pear buds in full white stage

Peach bud at red calyx stageHave you ever heard the term "nipped in the bud"?  That's precisely what we hope won't happen to our baby peaches, pears, and nectarines tonight, when the low is forecast to be in the 20s.  This is the one case where we're lucky that we live on the shady side of the hill, since our fruit tree flowers (mostly) haven't opened up yet, unlike the trees on our movie star neighbor's farm, which are in full bloom.

As a fruit tree bud comes to life, it is less resistant to cold weather with every passing day, and scientists have come up with charts of critical temperatures, telling us when we should kiss those summer peaches goodbye.

Apples

Silver
Tip

Green
Tip

½ inch
green

Tight
Cluster

First
Pink

Full
Pink

First
Bloom

Full
Bloom

Post
Bloom

10% kill
90% kill

15
 2

18
10

23
15

27
21

28
24

28
25

28
25

29
28
25

29
28
25

Pears

Bud
Swell

Bud
Burst

Tight
cluster

First
White

Full
White

First
Bloom

Full
Bloom

Post
Bloom

10% kill
90% kill

15
 0

20
 6

24
15

25
19

26
22

27
23

28
24

28
24


Peaches

Bud
Swell

Calyx
Green

Calyx
Red


First
Pink

First
Bloom

Full
Bloom

Post
Bloom

10% kill
90% kill

18
 1

21
 5

23
 9


25
15

26
21

27
24

28
25

European
Plums

Bud
Swell

Side
White

Tip
Green

Tight
Cluster

First
White

First
Bloom

Full
Bloom

Post
Bloom

10% kill
90% kill

14
 0

17
 3

20
 7

24
16

26
22

27
23

28
23

28
23

Sweet
Cherries

Bud
Swell

Side
Green

Green
Tip

Tight
Cluster

Open
Cluster

First
White

First
Bloom

Full
Bloom

Post
Bloom

10% kill
90% kill

17
 5

22
 9

25
14

26
17

27
21

27
24

28
25

28
25

28
25

Tart
Cherries

Bud
Swell

Side
Green

Green
Tip

Tight
Cluster

Open
Cluster

First
White

First
Bloom

Full
Bloom


10% kill
90% kill

15
 0

24
10

26
22

26
24

28
24

28
24

28
24

28
24



Nectarine flowerYou can probably guess what stage your fruit trees are at just based on the descriptions, but I've included some photos here to help you decipher the differences.  Our peach trees are in the red calyx stage (10% kill at 23 degrees and 90% kill at 9 degrees), our pears are in the first white to full white stage (10% kill at 25 to 26, 90% kill at 19 to 22), and our nectarine has buds ranging from red calyx to full bloom (10% kill at 23 to 27, 90% kill at 9 to 24 degrees.)

As you can see, you often find an array of bud stages on a single tree, which is good for us because it means that a late frost is less likely to kill off all of our fruit.  Even though the currently open nectarine buds and Nectarine bud in first pink stagenearly open pear buds are probably going to die tonight, the less precocious buds on each tree might pull through, and I'm not overly concerned about our peach buds.

All of that said, I'm not sure I expect pears this year.  Although my sample size is very small, I've found that each of my fruit trees has produced flowers but no fruit the first year it blooms.  Perhaps the trees aren't quite ready to pour that much energy into making fruits but are willing to make flowers in hopes that their pollen might pass on the tree's genes using someone else's energy budget?  I'd be curious to hear if you've seen a similar strategy in your own young fruit trees.  If my hypothesis is correct, we should see peaches from the tree that fruited last year and also from the tree that only bloomed last year, nectarines from the tree that bloomed last year, but no pears.  Assuming we don't get any excessively cold weather in the next few weeks, that is....

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