The biggest problem with Dormex is that it's quite tricky to use appropriately. In order for it to work, you have to know how much chill you've had, how much chill your plants need to satisfy their dormancy, and when exactly to spray it (too early and it won't have the proper effect, and too late and you can burn the developing flower buds). It's a restricted use pesticide, anyway, so unless you have a pesticide license you can't purchase it. It's not a very friendly chemical (hydrogen cyanimide) either. Applicators cannot drink any alcohol 24 hours before or after the application, or they can become very sick. Applicators in Italy have died after using Dormex. It's not something I'd want to mess around with much at all.

Shading the tree by draping over jute sack and wetting the jute sack during the early morning hours should boost your chilling hours. Another good setup is to install a misting contraption that fires up automatically every early morning till a couple of hours past sunrise, along with shading the tree during the winter. The evaporative cooling effect should drive down the surface temperature of your tree to achieve the chilling effect in marginal climates of zone 10.

Thanks for your responses.
Fruitgirl, it sounds like spraying with Dormex is definitely a a job for professionals. I wonder if my local tree maintenance company offers that service.
JoeReal, I googled jute sacks and they seem pretty pricy. Where do you buy them? Perhaps old sheets would do the same thing? My European plums are the ones Im most worried about, after BavayÂs Gage refused to sprout out over three feet last year, lost the whole top leader. I transplanted it back into a pot, and have all those plum pots on their side, in the shade, in what seems to be the coolest part of the yard. An experienced nurseryman suggested keeping them horizontal for winter, once dormant. There seems to be a cooler "climate blanket" along the ground that frosts over, when the "official" temps are as much as five degrees higher. No signs of flower buds yet, unlike some of my apple trees.

I doubt that any tree service would do this. I don't think Dormex is used at all in the ornamental or landscape industry, so I wouldn't expect any such service to be experienced with Dormex. They might be able to purchase it, but if they don't have experience in using it, you'll likely end up with a bigger mess on your hands that if you hadn't applied it at all.

A white old sheet would be better than jute sacks. Laying horizontal over open lawn should help in keeping it cooler to take advantage of a reradiating surface (lawn) to achieve cooling effect at night. The key word is "open", not under the eaves or under the trees.

On the other hand, bending the limb into horizontal position generally will induce early blooming, and I don't know if it helps in a low chill area.

I just completed 12 hours of research on the internet on how to defeat lack of chill hours. Dormex is best and from what i have read not near as "tricky" as far as application time if you follow their instructions. However, here in Texas, you cannot even purchase it except certain years when approved by the Dept of Agriculture. It requires an applicators license and SPECIALIZED safety equipment. Forget it in a home situation. What does work on stone fruit and is not very dangerous at all to apply is 2L Armobreak + 4L Armogen + 10ml gibberelic acid (GA3) per 100L of water. You could scale it down for smaller applications. Mostly sold in large quantities. I am looking for a supplier to sell me smaller quantities. Also works on apples, persimmon, grapes. You can look up the mixing formulas at www.campbellchemicals.com. Another formula that works almost as good (supposedly) is Armobreak + potassium nitrate applied 3 to 5 weeks before anticipated bud break. Be warned that too late an application or too strong a mixture or very warm weather after application can seriously injure your trees.

Thanks Don for all your hard work. Let me know if you find a supplier for small quantities of a dormancy spray. Armobreak was described on the IAAS website as a "Eco-friendly solution to overcome deficient growing conditions for deciduous fruit". Sounds like it would work.
One of the lawyers in a local rose club earned his applicator license. He blasted his roses every Sunday morning, joking "First you spray, then you pray." Quality safety equipment is a must with the high powered chemical combination sprays some rose exhibitors use.
Below is a thread from Gardenweb regarding chill factor that seems to have been deleted. It gave me the idea for Dormex.

Cheating for chill
http://forums2.gardenweb.com/forums/load/fruit/msg1203412322352.html?11

Posted by JoeReal Ca z9/SS z14 (My Page) on Tue, Dec 6, 05 at 10:46
You can spray with Dormex at the proper time, it can give you up to 750 chilling hours equivalent.
Or you can spray daily from mid winter to spring, with water from your hose at the coldest time of the day, like starting 6:00-7:00 am. This is supposed to "wash-off" the inhibitors that prevents premature blooming, but I haven't really tried this one. This is one of the experiments I am going to try.
Or you can use my portable flodable ice box. I have successfully bloomed and fruited a high chill colonade apple with this one. Ideal for short columnar plants. Look at My Page in this forum.

Posted by fruitnut z7,4500ft SW TX (My Page) on
Tue, Dec 6, 05 at 13:28
Short of using Dormex, there is not anything easy that will make much difference. Ice will have little to no effect. Remember that only temp between 34-54F are effective, with 37-48F fully effective. So ice at 32F is too cold and cann't easily be applied to the buds where cooling is needed.
Evaporative cooling, such as spraying the trees with water when temp is above 48F, can be effective. To work you must have a low dew point, ie, dry air. It would be most effective on clear, dry, sunny afternoons. This is what I'm doing in my greenhouse. But unlike outside, I can cool the air passing thru the house. Outside you would have to wet the trees every 5-10 minutes.
In my greenhouse, I can lower the afternoon temp by 10-12F below the outside temp by using the evaporative cooling system. For the 21 day period Nov 15 thru Dec 5, I've accumulated 415 Utah chill hrs; an ave of ~20hr per day. To do this required maintaining a minimum night temp of 37F using the greenhouse heater. Outside temp have ranged from ~20F to ~70F. Outside chill hrs are probably 100 to 160 Utah hrs but are very hard to estimate because the temperature has been swinging wildly from too warm to too cold.
If your nights are too cold, which I doubt is your problem, there is very little you can do about it short of an elaborate shelter and heater. My greenhouse with double inflated poly and a shade cloth over the plants provides no more than 1-2F temp rise above ambient ouside temp unless I use the heater.
In short, if you really need more chilling try Dormex.
The Fruitnut

Posted by JoeReal Ca z9/SS z14 (My Page) on Tue, Dec 6, 05 at 14:51
Ice can be effective and it works really well if you know the mechanics of how it is done, it is all in the Physics. If you apply ice to be in contact jaggedly at the surface, it doesn't mean that the surface will have ice temperature most especially if the air temperature is well above freezing point of water. There are air spaces in between the ice cubes. As the ice receives heat from the air or radiation or in contact, it melts due to latent heat of fusion but it cools the air surrounding it. Thus the surface will never be colder than 32 deg F, given the context that you are using it. It is in fact the cooled air that will cool the enclosed branches, not much the contact points of ice. That cool air within the enclosed ice box, I have measured is about 36-38 deg F when incoming air temperature is 45 deg F. As the air in my foldable ice box gets cooled down, they drain slowly (gets heavier and moisture laded from ice) and being replenished by the warm air at the top which in turn cools down slowly, creating ambient environment surrounding the enclosed tree branches to the perfect range for accumulating chilling hours. We measured this in my kid's science project. Physics is really great.

Posted by kuffelcreek z9 So. Calif. (My Page) on
Tue, Dec 6, 05 at 16:34
High-chill apples can easily be induced to fruit in almost any climate by stripping the leaves off by early spring. Gary Matsuoka at Laguna Hills nursery has done this for years, as have other CRFG members in Orange County (250 chill hours). Apples are grown in many tropical climates this way, including Nicaragua, Honduras, Thailand, and Indonesia. I do not know if it will work with other stone fruits (it doesn't work on peaches).
Another study cites that wetting the tree often through winter causes the growth inhibitors to break down.
Here is a link that might be useful: Laguna Hills Nursery, Apples