bonsaiTALK Community - View Single Post

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

3-Apr-2007	#2
Brent Evergreen Gardenworks Join Date: Sep-2003 Location: Northern California Country: US USDA Zone: 8 AHS Heat Zone: ? Posts: 309	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