CRF and Dormancy

marc5(6aOH)November 21, 2013

I started a lot of containerized trees this year (mostly pawpaws), and used controlled release fertilizer (CRF). Most was Osmocote 8-9 month. They were started in a high tunnel. As the summer progressed, the sides on the tunnel were open. Even with temperatures at or below freezing this fall, most of the trees held their green leaves, seeming to delay dormancy. I moved them into an unheated barn recently as temperatures dropped into the teens. The leaves are still on the trees.

I read some research indicating that CRF may interfere with dormancy, as it continues to fertilize the tree late in the growing season. I would appreciate any ideas or experience anyone has with this issue. I hope my trees survive the winter.


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marc5, pawpaws (Carica papaya) is a tropical and evergreen crop. I expect that it will grow as long as temperature, water and nutrients are adequate. Flowering and fruiting are triggered by shortening days.

    Bookmark   November 23, 2013 at 3:05PM
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shazaam(NC 7B)

I suspect that Marc's growing Asimina triloba, not Carica papaya.

    Bookmark   November 23, 2013 at 3:28PM
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Yes, I am referring to the North American Pawpaw, Asimina Triloba. But my query relates to any plant and dormancy.


    Bookmark   November 25, 2013 at 1:31PM
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tapla (mid-MI z5b-6a)

Decreasing photoperiod is the primary impetus that drives dormancy, with chill sealing the deal and moving the plant into its true dormant phase. After the plant is dormant, a certain number of 'chill units' is required to release the plant from dormancy. Once the plant is technically released from the grip of dormancy, it can be stimulated to growth at any time - usually after the plant has seen several consecutive days of soil temperatures higher than 45*. Once the onset of growth appears, the plant will have lost most of it's resistance to chill, and will need protection from temperatures near freezing and below.

There seems to be some sort of forgone conclusion that you should stop applications of N as fall approaches. You'll find mostly anecdotal evidence suggesting this as appropriate, but little if any, scientific evidence. In some circles convention dictates we only fertilize while plants are actively growing, or from bud break through late summer. I often see it contended that late (fall) feeding of N is sure to 'force' new growth and the new growth will be killed by frost.
But first, all tender new growth is killed by frost. Second, and probably more importantly, please consider that bud set occurs in mid-late summer, and while it takes N to fuel new growth, N plays no role in the initiation of bud-break. For that stimulus, look solely to photo-period. No one turns off the N supply where trees occur naturally - yes?

The acquisition of resistance to chill is related to both photo-period and decreasing temperatures and is actually improved with regular balanced N supplementation, so there is no reason not to continue supplementing N through fall and into early winter. Let your guide be soil temperatures. As long as soil temps are >55* plants will assimilate and store not only P & K, but N as well. This (tendency to store N) plays a pivotal role in fueling new growth in spring when soil temperatures are reduced and assimilation of N is depressed. BTW - please do not fertilize with organic sources of N like various meals, fish/seaweed emulsions, or urea when soils are cooler than 55* (ammonium toxicity).

Too, release of nutrients in CRFs are almost always controlled by temperature, so as temps decline, nutrient release declines as well. Even if late fertilizing did play a part in delaying dormancy, it would still be difficult to imagine how CRF could play a significant part, given that nutrient release is temperature controlled.


    Bookmark   November 25, 2013 at 4:42PM
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drew51 SE MI Z5b/6a

One major problem with fruit trees is how well they respond to fertilizer. Mature fruit trees in general are not fertilized, unless deficiency symptoms are noticeable. Each group of plants has unique responses and needs, For example some plants grow more with decreasing light. Some tropicals behave this way as in their environment it's the best time to grow. It's cooler, less chance of failure. Citrus often fruits in the winter. Some plants cannot respond at all to day length. Such as day neutral strawberries.
Currently the warmest part of your tree is the roots, as soil is slow to cool. Your trees should be OK, even if you get some tip damage. Be careful leaving them outside, not too wet. You don't want the roots to freeze. You have some protection, they should be fine.
Fruit trees often hold their leaves showing no fall change, so don't be concerned about that. My peach trees leaves always die green.
I don't have much experience with trees in pots, but plan next year to winter some blueberries in the garage in pots.
I will water them maybe once a month, so they do not completely dry out, but I don't want the roots to freeze either. Barely moist.
One could also pile straw on them to insulate them somewhat. In my garage the house keeps it warmer than just outside, so I expect temps not to drop extremely low. But in your barn, you may want to bury them in straw, pine straw, or leaves. If they get soaked with water, and it's below freezing for a long time the roots will die. The ground never freezes very deep, but pots do! Putting the pots in the ground would be the best way. Even if in ground, I still would put hay, needles or leaves on them, or mulched with something. Protect the base of the tree with wrap or guards to keep voles or other vermin from stripping the bark. You could add moth balls around the tree, or other rodent deterrents sold commercially, many contain mint, that works well. Often with hay the mice and voles love to live there., It's warm, and free food! (bark).

Let us know how it goes, so we all can learn from your experience. I look forward to hearing from you in the spring!
Good Luck!

    Bookmark   November 26, 2013 at 11:46PM
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drew51 SE MI Z5b/6a

Sometimes experience with certain plants is critical to understand what one is doing. What Al describes is correct and is exactly why you do not want to fertilize fruit trees in the winter. Fruit tree orchards are not growing lush trees, they are growing fruits. A well fed plant produces terrible fruit. Even holding water from them produces the best possible fruit.
So fertilizing fruit trees in the winter is terrible advice.
Unless you happen to like tasteless fruit? If that's the case I would suggest just going to the supermarket, where tasteless fruit rules the day. What we produce in our backyards blows it away! These actions come with consequences. Most peach trees are only good for 15 years or so, as the stress put on the tree to produce excellent fruit, takes it's toll.
As Marc explained to me elsewhere he plans on using the trees for grafts, so his actions with fertilizer make perfect sense. But if growing these trees for fruit and not scions, you would want to stress the trees.
What's great about fruit trees in pots is you can control the water. Fruitnut and others members produce some of the best fruit with super high brix levels. The pictures he has uploaded are unreal. It makes me want a greenhouse! Check out his posts in the fruit forum or on DWN forums.

Here is a link that might be useful: Fruitnut's water deficit nectarines

    Bookmark   November 27, 2013 at 10:53AM
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shazaam(NC 7B)

The recommendation to withhold fertilizer from container plants in late summer/ early autumn has always puzzled me. As Al said above, "no one turns off the N supply where trees occur naturally..." Hence, it would make sense that the onset of dormancy should be determined by other factors (temperature and photoperiod, as Al explains). After all, even if you don't fertilize your in ground trees in late summer/early fall, their expansive root systems will still have access to nitrogen in the soil -- it's not like the biological processes that create plant available nutrients shut down on August 15th. I think it would be obvious that you don't want to fertilize in excess in the fall (what would be the point?), but I don't think that sounds like what the OP has done in this case. Again, as Al points out, the CRF (assuming that it hasn't already released all of its nutrients) will slow down release rates by design as soil temperature declines.

This post was edited by shazaam on Wed, Nov 27, 13 at 12:53

    Bookmark   November 27, 2013 at 12:26PM
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Oxboy555(Las Vegas)

Questions for Al or anybody re:

"This (tendency to store N) plays a pivotal role in fueling new growth in spring when soil temperatures are reduced and assimilation of N is depressed."

--Don't soil temperatures increase as we get into spring?

"BTW - please do not fertilize with organic sources of N like various meals, fish/seaweed emulsions, or urea when soils are cooler than 55* (ammonium toxicity)"

--Is this only for container plants or in-ground plantings as well?

    Bookmark   December 5, 2013 at 8:09PM
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tapla (mid-MI z5b-6a)

When soil temperatures are reduced means when they are low, and particularly when they are in that sub-55* range. There is little biotic activity in soils then, which means little cleaving of hydrocarbon chains, so plants that have stored N realize an advantage. This holds true for in-ground plantings AND container plantings. I don't fertilize when mean temps are below 55* or above 85*.


    Bookmark   December 5, 2013 at 9:31PM
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