[mntlblok]

Was surprised to find some little patches of frost on the lawn early this morning. Did a bit of googling and was even more surprised to learn that, with the right set of conditions, ground temperature can be as much as 10 degrees cooler than the temperature five or so feet above the ground - the height at which temps are reported. What Causes Frost?.

Reminds me. We're giving the hobby of tropical hibiscus one more try. Any fellow enthusiasts looking in here?

[CoachKandSportsguy]

Originally Posted by mntlblok

Was surprised to find some little patches of frost on the lawn early this morning. Did a bit of googling and was even more surprised to learn that, with the right set of conditions, ground temperature can be as much as 10 degrees cooler than the temperature five or so feet above the ground - the height at which temps are reported. What Causes Frost?.

Reminds me. We're giving the hobby of tropical hibiscus one more try. Any fellow enthusiasts looking in here?

just plant it close to the house, and monitor for freezes and cover

[Pondboy]

Hibiscus will get a bit cranky under 40 degrees where they show their displeasure by dropping leaves.

I’ve invested in a few “Frost Blankets” (Amazon) which help to a certain extent. They reduce wind and keep temperatures inside about 3-5 degrees or so warmer than the outside temp.

I got very lucky and had 3 of them survive down to about 19 degrees a few years back. There was some dieback of the branches, but they are still alive today.

If yours are too big to handle (for a frost blanket), you could always prune them back a few feet in late fall so that they fit under the frost blanket.

[Two Bills]

Cover plants, or turn sprinklers on intermittently when frost is about.
Leave pruning until after risk of last frost, and then cut back to limit of any damage.
Most shrubs can take a good haircut, and many are stronger for it.

[mntlblok]

Originally Posted by Pondboy

Hibiscus will get a bit cranky under 40 degrees where they show their displeasure by dropping leaves.

I’ve invested in a few “Frost Blankets” (Amazon) which help to a certain extent. They reduce wind and keep temperatures inside about 3-5 degrees or so warmer than the outside temp.

I got very lucky and had 3 of them survive down to about 19 degrees a few years back. There was some dieback of the branches, but they are still alive today.

If yours are too big to handle (for a frost blanket), you could always prune them back a few feet in late fall so that they fit under the frost blanket.

Most excellent info for dealing with "hardy" hibiscus. Been trying to study up and it looks like the "tropical" versions are something like 15° more finicky. Working on a plan. . .

[CarlR33]

I saw small amounts of frost on the North facing roofs of several homes and I live in the Southern portion of the villages where you would think it would be warmer, LOL

[Pondboy]

I also have “rock mulch” which creates a “micro climate” to keep the ambient temperatures up. Also, it’s not just how cold it gets but how long it’s cold for. My hibiscus are on the east side so they get the early morning sun.

[MandoMan]

Originally Posted by mntlblok

Was surprised to find some little patches of frost on the lawn early this morning. Did a bit of googling and was even more surprised to learn that, with the right set of conditions, ground temperature can be as much as 10 degrees cooler than the temperature five or so feet above the ground - the height at which temps are reported. What Causes Frost?.

Reminds me. We're giving the hobby of tropical hibiscus one more try. Any fellow enthusiasts looking in here?

Sometimes around here in the winter what looks like frost is just heavy dew on the golf courses. Rub it with your hand or foot and you can tell for sure. That said, yes, there are “microclimates” that may be only a few square feet or yards where the temperature can be quite a bit different due to such things as a warm wall nearby, or foliage that slows a breeze, or something like that.

[Danube]

Originally Posted by MandoMan

Sometimes around here in the winter what looks like frost is just heavy dew on the golf courses. Rub it with your hand or foot and you can tell for sure. That said, yes, there are “microclimates” that may be only a few square feet or yards where the temperature can be quite a bit different due to such things as a warm wall nearby, or foliage that slows a breeze, or something like that.

Frost all over many roofs & lawns up north this morning. Probably the 5th time this season, today was the heaviest.

[mntlblok]

Originally Posted by Pondboy

I also have “rock mulch” which creates a “micro climate” to keep the ambient temperatures up. Also, it’s not just how cold it gets but how long it’s cold for. My hibiscus are on the east side so they get the early morning sun.

Sounds right. Tricky business here in 9B. Currently having some success with propagating cuttings in an effort to work around the issue. "Domes" (for humidity) seem to be key in my efforts, although they really seemed to take off once I put that little heating pad for seedlings under them.

I *think* that all the pretty, multicolored-blooming hibiscus that we've gotten from the big box stores this year fall into the "tropical" category. We decided not to test them outside through the winter months. Dug em up and put em back in pots - after taking the cuttings. So far, so good. Testing some cheapo "grow lights", too.

[FredMitchell]

Originally Posted by mntlblok

Was surprised to find some little patches of frost on the lawn early this morning. Did a bit of googling and was even more surprised to learn that, with the right set of conditions, ground temperature can be as much as 10 degrees cooler than the temperature five or so feet above the ground - the height at which temps are reported. What Causes Frost?.

The description of radiational cooling in the link is not strictly accurate. It is not radiation into the air or atmosphere. Radiational cooling is radiation (black body radiation) not getting reflected back down. So it escapes the earth's atmosphere as radiation. Cloud cover, or an overhanging tree, prevent or reduce this. The tree will even be radiating toward the ground, which is why you often have frost on a lawn except under trees.

"Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics" is a nice little book that explains this, as well as other interesting things like why mountains in the distant look more grayish or blue. It is sort of a college text in atmospheric physics for art majors, so it is pretty approachable.

[mntlblok]

Originally Posted by FredMitchell

The description of radiational cooling in the link is not strictly accurate. It is not radiation into the air or atmosphere. Radiational cooling is radiation (black body radiation) not getting reflected back down. So it escapes the earth's atmosphere as radiation. Cloud cover, or an overhanging tree, prevent or reduce this. The tree will even be radiating toward the ground, which is why you often have frost on a lawn except under trees.

My palms start sweating when black body radiation comes up, so I'll take your word on that inaccuracy. :-)

[HORNET]

If it freezes out, pull it out and put a rock in its place. Learned on first house!

[GoldenBoy]

Really? What causes frost?

[GoldenBoy]

Originally Posted by FredMitchell

The description of radiational cooling in the link is not strictly accurate. It is not radiation into the air or atmosphere. Radiational cooling is radiation (black body radiation) not getting reflected back down. So it escapes the earth's atmosphere as radiation. Cloud cover, or an overhanging tree, prevent or reduce this. The tree will even be radiating toward the ground, which is why you often have frost on a lawn except under trees.

"Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics" is a nice little book that explains this, as well as other interesting things like why mountains in the distant look more grayish or blue. It is sort of a college text in atmospheric physics for art majors, so it is pretty approachable.

Really, bud don't encourage these questions.