Frost in the Future

rockm

April is the most challenging month for bonsai in my area. This year is proving to be no exception. I've finished most of my repotting. Trees are leafed out--daytime temperatures are in the low 80s--life is good.

However, a hard freeze is forecast for Thursday and Friday nights--below 27 F. That can be a death sentence for most of my trees. I will spend Thursday moving things around outside and some inside to minimize exposure to the freeze.

It figures I just picked up my big live oak from storage on Saturday. I will have to lug the big #$%^&!* inside for two days to wait out the frost . Normally, I wouldn't, since it is so big, it's soil mass protects it from snap overnight freezes. However, it was repotted and heavily pruned on Saturday, so there is some vulnerability to consider.

Those of you in the East, beware. This weekend could be a killer.

Oh, by the way, those of you that can make a trip to Gardens Unlimited in Ladysmith, Va. and are into tropicals should go soon. The nursery just got a big shipment from Fla. Saw some pretty nice elms and ficus, but also some really big Bucida (Black olive)--some two inches in diameter and 24 inches tall for not much $$. One largish semicascade stock was marked $65....

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Brent

Rockm et al

You folks have my sympathy. I have to deal with this problem every year for the entire nursery. It was the one big drawback to moving the nursery to a small coastal mountain valley that is a cold sink. We have the coldest temperatures of any reporting weather station in the area, typically five to seven degrees F colder than around the lake and larger valley.

After suffering enormous losses in the early years, it became apparent that I would have to adopt a frost protection system similar to the vineyards here. Grapes are especially susceptible to freezing weather once they bud out. They cannot tolerate any freezing at all. The growers manage this by turning on overhead irrigation, rainbird impulse sprinklers, for the whole vineyard for the duration of the frost. This of course, takes hundreds of thousands of gallons of water and huge diesel pumps. All the areas must be on at the same time, rotating sections doesn't work. Most store water in ponds to be used for this purpose and will often empty these ponds in a night or two and then recharge them in the following days.

The sprinklers coat the vines in ice which continues to thicken as the temperature drops. Down to about 24 or 25F this will keep the vines at exactly 32F. This occurs because as water freezes it releases heat, called the heat of crystallization. Luckily, water has a very high heat of crystallization, so a lot of heat is released when water freezes. This heat keeps the temperature from dropping any lower than the freezing point. Colder than about 24F, you simply cannot apply enough water to keep the temperature from dropping further and often the sprinklers will begin to freeze up at around 20F.

I have adapted the same techniques for the nursery, except that it was not realistic for me to coat the entire place in ice with rainbirds. I just don't have the water capacity or the proper layout to do this. Instead, I developed a more localized frost protection system using micro sprinklers instead of rainbirds. These put out a tiny amount of water compared to rainbirds, but can be used in small and odd shaped areas since the effective diameter is only about ten feet or less. My liners (small pots) are in long shade cloth covered hoop houses fourteen feet wide and one hundred feet long. I changed the heads on my irrigation to these very reliable micro sprinklers for both irrigation and for frost protection. I also have a three thousand square foot shade house that also employs these microsprinklers.

In winter, I remove the valves to these areas from the controller and put them on a thermostat. For spring frost control, I set the thermostat at 32F. So when the temperature drops to this point, the frost protection comes on automatically, I don't even have to get out of bed. The system works marvelously. It has virtually ended my losses of small plants to spring freeze damage. However, I still had the problem of my landscape plants being damaged by spring freezes, especially my Wisteria and fruit trees. So, I adapted the microsprinklers to spray a circle of water above each tree and vine. It was a lot of work to set up, but it does protect them nicely down to about 24F. This year we got a good test. I recently improved the emitters by putting a six inch ring of one eighth inch hardware cloth around it. This diffuses the spay and puts nearly all the water in a tight circle just including the tree. We had one night so far this year that hit 23.7F. The trees made through fine, no leaf or flower damage. The Wisteria however lost most of their flowers, but not all. Since the Wisteria is so tender, this was a really good test, and I think this is the best that I can expect.

My well and 2hp pump can produce about 30 gpm at 30psi which allows me run about 100 microsprinklers. My current plans are pushing this limit. To get more protection than this I would have to install a doughboy type swimming pool with a separate 1hp pump to use only for frost protection (and to keep the wife happy in summer). A ten thousand gallon pool would give me four hours of protection for about another 50 sprinklers. The plumbing infrastructure is set up to accommodate such an addition.

A separate issue was how to handle winter freeze damage in winter (see the Article at our website on this problem of exceeding the minimum low temperature for woody plants). This area is considerably colder than the old nursery. Many of our plants are new cuttings with very succulent roots that cannot be allowed to go below about 25 or 26F the first winter. Early on, I discovered that if I left the irrigation system on during freezing winter nights, I could prevent most of this damage. However, the use of the microsprinkler system on the thermostat has greatly improved the effectiveness and efficiency of this system. Now, in winter when the temperature drops below 30F, the hoop houses and the shadehouse irrigation systems are turned on by the thermostat and turned off again when the sun comes up and warms above this temperature. I tried to get the thermostat temperature down to 28F to save water, but the sprinklers often freeze up and won't work when attempting to start at this temperature. This is a very cheap heat compared to greenhouses. It costs about $30 a month to pump enough water to maintain this protection (almost six thousand square feet).

We got a really good test of the freeze system this January. We had the coldest two week period in about eight years. The low temperature for the period was about 12F, but every night for two weeks it was below 20F. The system froze up after the first really cold night, but by then everything was encased in a gigantic block of ice that took weeks to melt. The system has a drain down feature, so that during the day the risers thaw and can operate again the next night even with six inches of ice everywhere on the ground. I keep a max/min thermometer in one of the hoop houses all winter to see what the lowest low will be. With the freeze system this year, the coldest it got in the hoop house under the ice was 25F even after an ambient temperature of 12F. The biggest test was whether or not my very tender (and valuable ) Trident maple cuttings would survive. They did.

What does this mean for you? You don't have to be a rocket scientist to devise such a system. All you need is water, a hose, and a sprinkler. When you suspect that the temperature will fall below freezing at night, simply turn on the hose before you go to bed. Turn it off when the sun comes up. You do have to use some common sense though. If the water doesn't reach all the plants, the ones that don't get coated with ice will be vulnerable. Ice is heavy. If you have long branches on trees in training, the ice may weigh down and break these branches just like an ice storm (which is what it is). For bonsai, this usually isn't a problem since the plants are so compact.
It may take some playing it with, but this can be a cheap, effective, and labor saving system of spring frost protection.

Brent
EvergreenGardenworks.com
see our blog at http://BonsaiNurseryman.typepad.com

chansen

Thanks for the heads up rock, and thanks Brent for the wealth of information you've shared.


I too am looking to the weekend with a little trepidation. I repoted this last weekend as well, and even though I don't have anything 'world-class' I'm not in the position to be able to easily replace what I do have. The weather even ruined my plans to go backpacking this weekend.

Rock - losing that live oak would be terrible. My sympathies for having to move it around, it is big. Luckily Richmond temps. are only dropping into the 30s, so I'm hoping that with them up against the side of my apartment and clear plastic over them for the night, that everything will be ok.

Good luck with the weather, and I'll have to get up to Gardens Unlimited again soon, I need another elm.

Christian

Ian_Homer

Brent,

Great post and thanks for the explanation.

Not suffering severe winters here, I had not heard of this technique until I saw the pictures on Walter Pall's Webpages/Blog.
http://walter-pall-travelogues.blogspot.com/index.html

Pity we have just gone on a Water Meter at home, but doubt I will ever need to run such a system here.

Regards,
Ian.

rockm

Brent, thanks for the excellent insight into how to handle shallow freezes.

I have been wondering if the ice thing will work for my trees, but since I live in a townhouse community, leaving the water on all night long can cause some flooding issues--not to mention some dimwitted comments from the neighbors and property board .

I am stuck, I'm afraid, lifting 100-200 lb trees-along with about twenty 30-50 lb trees-- and moving them inside or into covered cold frames for the duration of the freezes. I leave my winter set up --mulch piles and cold frame--in place until mid-April, sometimes until the end of April.

The heavy lifting wasn't a problem 10 years ago, but my back ain't what it used to be. On the bright side, my son is growing up and in the next few years HE will be the designated labor .

So, my advice, grow your own help, as well as trees

rlist

Rock-

We have had similar issues here in Portland. All of my trees have been repotted - from 2 months ago to the most recent batch being last week. My maples are either leafed out or are in the process, and I have lots of new candle growth. So, any weather issues catch my attention as well.

That said, I learned over the past year or so that the best thing I can do for myself and my trees is to put them on the ground when it hits these temperature drops and leave them alone. I have about 80 trees that spent the entire winter outdoors, unprotected (save one night of 70mph winds) and on the ground - they all spent over two weeks frozen solid. I have not lost a single tree from this treatment either.

Now, I am not comparing our winter to yours, and long term cold in many areas should get a greater level of care than what I do - that is not what I am saying. It was 30 degrees here the past two mornings, and 28 degrees this morning. Out where JasonG (& Oregon Bonsai) is, they have patio furniture that holds an inch of water and every morning for two weeks they have had it frozen solid until about 10am when the sun hits the area. He, Oregon Bonsai, and I do nothing. Too many trees, too much time, and nowhere really to move them to.

So, I guess what I am really saying is that trees are a little more hardy than given credit for, and in many cases the simple act of moving them from the benches to the ground is quicker, easier, less painful and sufficient. If you are in a townhouse community, on the ground next to the house or fence is more than sufficient for a 27 degree night.

That's my two cents, for whatever it is worth...

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rockm

I think this depends greatly on the species you're dealing with. I have alot of Southern U.S. natives-- Bald Cypress, live oak, hackberry and the like. A drop into the mid to low twenties after repotting and pruning puts these species at risk. I might not move some of the big ones inside, but may opt to leave them under my deck against the house. The buds on some haven't opened yet, which helps a great deal. Some, however, have been pushing leaves for quite some time. This looks to be a near deep freeze coming--possibly below 25 F locally.

We had a very very bad patch of weather in Feb., despite the unnusually warm Dec. and Jan. There was deep, sustained cold for weeks, with lows between 3 and 10 F at night, and highs reaching only into the mid 20s in the day.

Sustained cold after a prolonged warm spell, I think, contributed to alot of die back on collected species, even the stuff I've collected locally. The mulch froze solid through to the ground in my storage areas--which isn't a good thing.

I had complete limb die back on native hornbeam and hackberry, with alot of partial die back of twigs and branches on other species, including Japanese maple and Korean Hornbeam. These were left only with a deep mulch covering over the winter. The trees in a covered cold frame did fine.

After 15 years of overwintering trees, this is the worst year I can remember.

rlist

[QUOTE=rockm]There was deep, sustained cold for weeks, with lows between 3 and 10 F at night, and highs reaching only into the mid 20s in the day.QUOTE]

Oh, good Lord... Yes, that is cold and dieback is expected with that! As for SE species, yes, you bring up a very valid point...

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Check out my new blog here...
Both gold and muck come out of the same shaft...

Mcspeed

Rock, try this, put up a tent so to speak over the tree/trees, then fill bottles, pans, or even fill a garden hose, with warm/hot water add those to the tent, around the trees. Also a good watering helps too, the heat exchange for water is fairly slow so it should keep the trees temps to where it shouldn't be a problem, especially if you start with a warmed water.

Good Luck, up here we had been getting up to 55-60-65 during the days, and dropping constantly into the low 20's, at least we expect that up here.

Jeez you went right from winter to sumer, but that seems to be becoming the norm rather than the exception.

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