Getting scared about tomorrow nights temps.

[stormymater]

Originally Posted by nctomatoman

Was it windy/rainy, Tom? I've had hundreds of seedlings outside down to 34 degrees two nights in a row with no ill effects. It is wet, lashing wind that really hits the plants and turns them ugly.

So you've been to Pleasure Island in the early spring,eh? I have the plan for trays & boxes of little plants - under the boat in the garage, in the back of the pickup beneath the topper, in the trunks of cars, in the studio apt - wall to wall - they are all coming in for one last time (hopefully)

[jsvand5]

Looking worse every time I check weather.com. Calling for 35 now. I think I am going to buy a bunch of those big contractor garbage bags. They should be able to cover almost all of my plants down to the ground I think. Not sure how much protection they will offer but I guess it's better than nothing. I am going to leave 1 or 2 types that I have more than one of unprotected just to see if they would have been fine without all of my worrying.

[creister]

Just remember, you don't need 32 to get frost. That mostly depends on humidity. Our air has been soo dry here. Last night the humidity was 15%. Of course, we haven't been getting any rain either.

[Worth1]

Originally Posted by creister

Just remember, you don't need 32 to get frost. That mostly depends on humidity.

Well yes and no read this article and it will explain how your thermometer might read above 32 but where the frost forms will be freezing.

Some Frost Science....

Frost is ice that sublimates directly on the surfaces on which it is found. Sublimation occurs when water vapor, goes directly from the vaporous state to the solid state. To fully understand frost deposition you must think in terms of energy. Water vapor is in a higher energy state than liquid water and liquid is in turn in a higher energy state than solid water (ice). For water to be maintained in a vaporous state, there must be a certain amount of energy available. As energy is removed from the air, i.e. the air is cooled, all the gasses loose heat. Nitrogen, Oxygen, Carbon Dioxide, Water Vapor and all other components loose energy. Eventually when enough energy is removed the vapor must change state and it becomes either liquid or solid. Each liquid water molecule has less energy than each vapor molecule and each solid water molecule has less energy than either a molecule of liquid or gas.
Dew Point Temperature and Frost Point Temperature

The temperature at which the change of state occurs as the air is cooled is called the dew point temperature when the change of state occurs at a temperature above freezing or the frost point temperature when the change of state occurs at a temperature below freezing.
What determines the temperature of condensation or sublimation is the amount of moisture in the air, the greater the amount of water vapor, the higher the condensation temperature. During summer it is not uncommon to have a dew point of 70°F in the eastern United States. But in the cooler seasons the dew point can be below freezing, in which case it is called the frost point temperature.
Dew or Frost Tonight?

Whether dew or frost will form is determined by two factors:

2. If the amount of moisture in the air causes the condensation temperature to be above or below freezing and
3. If the temperature will cool to the condensation temperature.

For more on dew point click here

Other Ices

There are other types of ice that can be found on surfaces.
If after dew forms the temperature falls below freezing a coating of glaze ice may result, sometimes called black ice or a black frost it is just frozen dew. If the amount of dew is scanty individual frozen drops will result.

But the low temperature was only 35°F, How did frost form?

What is important is not what the temperature was at the thermometer but what the temperature was where the frost formed, and if frost formed the local temperature was below freezing.
A thermometer indicates the temperature where the thermometer is, usually a few feet above the ground. Because cold air sinks relative to warmer air and because the ground can cool very quickly the temperature at ground level can be cooler than a few feet higher where the thermometer is, eventhough the thermometer indicates a temperature that is above freezing, it can easily be below freezing a few feet lower.
For more on LOW TEMPERATURES click here


What about my car it is above the ground and there was frost on it?

Certain materials like glass and car metal radiate heat quickly and therefore cool quickly. Also, areas like rooftops or high plateaus, because of their exposure lose heat through re-radiation very quickly and tend to receive frost before sheltered areas.
On marginal nights frost may only be seen on rooftops and cars and spotty grassy areas, because of location or materials these could cool below freezing while nearby areas remained just above freezing and received no frost.

But some areas had dew, others had frost....some areas nothing at all!...How can that happen?

In the same way temperature varies in very areas in close proximity to one another, the amount of water vapor varies too. An exposed parking lot may have less vapor in the air than a nearby garden because the a plant canopy traps water vapor and plants transpire (emit) water vapor.
In the garden there may be enough vapor so the condensation temperature is a dew point temperature, while in the parking lot the condensation temperature is a frost point temperature. If the air over each cools to the condensation temperature dew would be found in the garden and frost on cars in the parking lot.
If the temperature continued to fall after dew and frost formation, the parking lot may end up with a heavy frost and the garden with black ice, that is frozen dew.





Worth

[habitat_gardener]

SInce you're planning to have a few sacrificial plants anyway, I'd experiment with covering the top of some plants, if you have an easy way to do that -- bedsheets? The newest leaves and the growing tips seem to be most vulnerable, and at my garden the most vulnerable time seems to be when the dew falls.

Or you could do what some of the orange growers (used to?) do, and be out there in the middle of the night with a heater.

Or, if you have a big umbrella or two, or one of those portable gazebo things, you can set that up.

[jsvand5]

Well the wind ended up dying down and we got down to 34 so there was a pretty heavy frost. I ended up just covering everything with 55gal garbage bags. The only damage I got looks to be leaves that were in direct contact with the bags since the bags were covered by frost in the morning. Didn't have time to really see how the blooms did but all the plants made it.

[nctomatoman]

Apparently it went to 34 in Raleigh - my wife indicates nothing got hit (the eggplants and peppers were under double Reemay - will be interested to see how the lettuce in my garden did, but as long as it didn't hit 32, expect things to be OK).

Whew. still, I am glad all the tomatoes were in the garage, despite the effort to get them all back out tomorrow evening!

[stormymater]

Got to 37 here last night - everything is outside & uncovered now, soaking up the warm sun (whew is right!)
All the little tomatoes looked happy - the ones in the truck actually looked like they GREW overnight! Took a full 30 minutes to uncover & move all to their places in the backyard. I did experiment with a bunch - put them in between the new raised beds, closed the ends with bales of straw, laid window screens across the raised beds (creating a 20 inch high covered area between beds) & laid down a big silver tarp weighted down with bricks, cinder blocks, yard ornaments & a few CRW tomato cages as the winds were whipping yesterday afternoon. They look great too!
I am so glad we covered & moved them.
Don't want to do this again though.

[Deer Park]

Don't know what temp it was a few nights back but I lost around 20 plants and had about 150 get hit with leaf damage. Another 150 plants show no signs of damage. I did'nt cover anything as the forcast was for only a low of 39 in our area but it was later reported that areas just west of us got to the low 30's so maybe we did also for a little while. I will plan to regrow those varieties lost in the fall garden. I have taken suckers but may not get fruit before the heat gets them late June early July. Got to try.

What about you other Greater Houstonians?

Michael

[Mojo]

Both of my beds sit next to a northwest-facing picket fence 7' high, so the wind damage has been somewhat mitigated. I had frost the other night on the grass, and the groundling cukes did NOT have a good night. But my maters were sitting on high furrows and evidently suffered no damage.

[Fusion_power]

My tomatoes were prudently in the greenhouse and came through the 28 degree temps just fine thanks to a good wood heater. I kept the temp in the greenhouse between 41 and 45 degrees even at the coldest time of night.

Some of my customers in Texas were not so fortunate. One person lost all of their plants.

DarJones

[ContainerTed]

My screened in porch, which gets a little heat off the main house, showed 31 F at 7:30 AM Wednesday. Plants went back to the porch yesterday afternoon, except peppers and tomatillos.

Ted