Frost topic

[nexxogen]

I couldn't find a better spot to post this on the forum, so here it goes. After hours spent on googling, I couldn't find definitive answers to these questions, so I hope someone will be able to answer them here.

1. I know that a low dew point can be an indicator of frost if the air temperature is near freezing. As far as I understood, the harmful ice crystals form before the dew appears in such conditions. I also know that there's frozen dew, which happens when the dew forms first and then freezes. My question is - is frozen dew harmful to frost sensitive plants?

2. Can frost ever form in rainy conditions, where the climate is such that the daily low falls a bit bellow freezing for a few hours only two or three times per year on average?

3. Where I intend to grow my subtropical plants, something looking like a white powder occasionally appears on the grass in winter mornings, but it's always only at ground level. Assuming that this is frost, can it harm fruit trees and if yes, will mulching around the base of the tree be sufficient to protect them?

[C24mccain]

 Hello, I'm not sure on one and two but I have a testimony on three... Here in Lakeland Florida we are just finishing up a week of cold mornings. Our lowest temp this last week was around 35 but it was at that temp for many hours.. That morning we had a light frost on the ground everywhere except under the tree canopies. No harm to any of my subtropical trees. Now I have a very thick mulch layer, over one foot in many areas. Since I typically keep the mulch a foot or two away from the trunk a bowl is created. Last year I planted some tiny figs in February that fit in the bowl. We had some temps around 35 and the leaves were burnt off them though I never saw frost. Curiously I put a temperature probe in the bowl. That night when it was 40* outside it was 32* in the bowl. This happens when there is no wind. That's why my figs got burnt because they were sitting down in a freezer.  Because of this I was worried about the trunks of my Tropicals so this last week I made the mulch layer even by filling in the bowl. I will remove the mulch from the trunks after winter so the trunks don't rot.. I hope this testimony helps.

[achetadomestica]

I also had a light frost on Monday morning this past week. I like to water the trees the night before.
I didn't water this past frost because we had 1 1/2" of rain the night before. I do know that my yard
has colder spots. I live on the end of my road and it is much higher then the front. The front half of my
road is constantly under water in the wet season and I have never had standing water in my yard.
It is always 1 or 2 degrees colder in the lower areas of my neighborhood. I have a friend that has
a temp gun and checked his yard on cooler nights. The air and ground temps were usually 5-6 degrees
different and there were colder pockets in his yard. I don't believe the mulch "bowl" caused the temp
difference? I mulch heavy and water heavy on cold nights. We were 38F at 4:30am and there was frost
everywhere on the ground. Younger trees would be more effected then mature trees, I brought allot of
my seedlings in but left a couple out.  Everything did well but this was not a deep frost?

If you haven't planted yet go outside on a cold night and look where the frost free places are and ideally if you have a temp
gun find the warmer places in your yard for your most sensitive plants. The South side of an oak tree will be
warmer then the North side in Florida. I planted sugar apples and sapodillas on the south side of my house in warmer
pockets. One day we will be back in the 20s and I don't want to lose all my trees.