Watering in morning to protect from Frost Damage??

I wanted confirmation on this as it is going to possibly frost tonight..... I think I read that if you have an overnight frost on tender plants and you water them before the sun hits them, there will be no damage.. Is this correct? The theory being that the sun hitting the frost is what actually causes the damage?? Anyone know about this?? I covered what I could and am praying for the rest, but will water before the sun comes up if that helps too. Any info please??

Also, I would like this info for future reference as well, so don't think your too late if your answer is not tonight!


Thanks

Susan


This message was edited Apr 27, 2005 7:10 AM

Understanding Frost

In spring and fall, the word frost sends gardeners scurrying for sheets, boxes, jars, floating row covers, the sprinkler system, or whatever they can scrounge to keep their plants safe from a possible cold snap. Just what is frost, and what does it do? How do your protective measures work?

There are two types of frost, advective and radiation. Advective frosts occur when a cold front sweeps into an area. Winds are typically gusty, clouds may occur and the thickness of the cold air layer may reach more than a mile high. One seldom sees the first frost of the season under these conditions. The first frost is typically a radiation frost. These occur under a clear sky and calm winds.

On overcast nights, cloud cover acts like a blanket on the Earth, trapping radiant heat from the ground. Any wind mixes the air thus trapped, creating a uniform temperature. However, clear skies and calm winds allow radiant heat from the Earth to rise to the upper layers of the atmosphere. Lack of wind prevents mixing of the air and an inversion layer develops. An inversion means that atmospheric conditions are inverse or opposite of normal daytime conditions when air temperature decreases with height. In an inversion, cold air collects near the ground while warmer air lies above this trapped cold layer.

The topography of the land also affects frost prevalence. Cool air settles at the bottom of slopes because it is heavier than warm air. Frost pockets will then form in valleys where cool air is trapped. Higher altitudes also have colder temperatures. Therefore you are apt to see frost damage at the bottom of sloped and on the hilltops, while the hillsides are frost-free. On any given property, there may be temperatures on different sides of the house, under protective trees, on south or north facing slopes, or in low-lying spots.

Frost warnings signal us that our plants may be in trouble. However, the essential criterion in damaging plants is not the appearance of frost, but the internal temperature in various tissues of the plant. If this is cold enough to break cell walls or disrupt cell constituents beyond repair, damage, wilting, and death will occur in affected tissues. Frost will not always cause this degree of chilling within plant tissue, nor is it the only cause.

Typically, we may have 3 – 5 weeks of good weather following a frost but the crops have already been damaged or killed. Rather than just talking about the weather, there are several things that gardeners can do to minimize the effects of the first radiation frost. These include.

Watch the calendar and the forecast. Know when the average first frost will be in your area. This is the date by which a frost will occur 50% of the time. In looking over weather records in upstate New York over the past 50 years, it seems that this date is coming later each decade (although the date of the last spring frost has not changed much). Keep a careful eye on the weather forecast, too. Cool, clear nights with low humidity, often following a cold front, are signs of an impending frost.

Beware the full moon? People have always associated the full moon with an increased chance of frost. However, in reviewing weather records of four locations in the Northeast for the last 100 years, a full moon did not increase the chance of a frost. It was just as likely to occur when no moon was present as when the moon was full!




Harvest early. A crop like tomatoes is very sensitive to frost. If you have no way to protect plants, you may want to harvest all fruit that are in the mature green stage of ripening. Fruit harvested at this stage will still ripen, albeit not with the same flavor as fruit harvested with some color. Place fruit in a single layer in a warm, dark location with some air movement. Tomatoes and other fruit do not need light to ripen. In fact, light will slow ripening. Store where the temperature does not go below 55F. Lower temperatures will cause the fruit to be poorly flavored.

Irrigate, before the frost. A moist soil can hold 4 times more heat than a dry soil. It will also conduct heat to the soil surface faster than a dry soil, aiding in frost prevention. In a study performed years ago, the air temperature above a wet soil was 5oF higher than that above a dry soil and the difference was maintained until 6 am the next morning. Thus, plants should be well watered the evening before a frost.

Cover your plants. Covering plants can give you 2oF to 5oF protection. The covers can be laid right over the crop, or can be supported on stakes. The difference being that protection is less wherever the cover touches the plant. Any material can be used to cover the plants, however woven fabrics are better insulators then plastics or paper. The best time to apply covers is in the late afternoon after the wind has died down. Remove covers the next morning before the sun hits them.

Irrigate during the potential frost. Many people claim that watering the frost off plants prevents frost damage. This is partially true. As mentioned above, watering plants helps raise their temperature and the air around them to that of the water. In addition, as water freezes, heat is released; 80 calories for each gram of water that freezes. Therefore, watering plants before they are injured from frost can help keep their internal temperature above freezing. A single application at the coldest part of the night (generally just before sunrise) may be enough on 30-32 degree nights. On colder nights it may be necessary to apply overhead irrigation for an extended period of time, allowing actual ice formation on the plants. In this case, irrigation must continue until morning temperatures rise above 32 degrees and the ice melts. It is important to note that once frost damage occurs, watering does not help.

Chemical sprays. Buyer beware! Many materials will claim to provide frost protection using a variety of techniques. However, no commercially available product seems to be able to stand up to a replicated, scientific test.

Heaters and wind machines. These measures are generally restricted to commercial growers and work best in orchards. Both are used to break down an inversion layer. Heaters warm the cold ground air, causing it to rise. This updraft causes a corresponding downdraft, thus mixing the air. Wind machines are huge fans mounted on 30-foot towers. The wind currents they create physically mix the warm and cold air layers.
Whatever frost protection measures we use, winter will eventually end our growing season. The time will come to say goodbye to our garden and begin chores left undone for so long under the pretext that “there will be more time in winter!”

9/2001 Compiled by Eric de Long, Cornell Cooperative Extension, Chemung County


This message was edited Apr 24, 2005 11:16 PM

My local news just reported the same thing... they said if you was the frost off in the morning, by 7:30 or so, there will be no damage to the plants... I'm going to try it...

I remember my Dad going out before the sun hit his frosty tomato plants...he sprinkled DIRT all over the leaves. He said that would keep the frost from hurting them when the sun came up....Does it work? It did for him. Jo

I have always gone out the morning of a frost and sprayed everything down
But it was usually in the fall....never tried it in the spring

soulgardenlove - wow, what great information. Are you Eric, or are you quoting from an Extension publication? I'd like to be able to reprint this information (with proper credits) in our Master Gardener newsletter.

And to think this comes to us from Georgia! (I would have thought we were intimately acquainted with frost in our neck of the woods.)

Marty

Hi Marty, Nope, I'm Susan.. I did a search on google and found this. The link was so long that it didn't work when I posted it, so I went and copied the info and deleted the faulty link. It was from a Cornell University web site.

Here's how you find it and it will be PDF form, so that may be perfect for your newletter.
Search Google" Understanding Frost Eric de Long, Cornell Cooperative Extension, Chemung County" and it comes up.

Yes, last night was a crazy fluke and it was a record low for about 47 years... But yes we get frost late down here too!
:)

Susan

Well, what did you end up doing?

I have washed the frost off plants before the sun hit them also. It does work in the fall. But, I haven't tried it on tender spring plants either.

Oh!! Hey Sidney! Well, I don't think it got that bad really... I didn't see any frost, but just to be on the safe side, I turned that sprinkler system on early this morning and washed off any possible frost :) I took all 40 bags off all my Tropical hibiscus and my two Meyer Lemons, and houseplants and that will be the last time til this winter when I bring them inside or into a greenhouse I dont have yet, but will!! :)

:)

Susan

Hey Joan,
Could there be any difference between a spring frost and a fall one in this aspect?? Would it matter if it was a different time of year and you used water to keep damage away??

Thanks!!

Susan

Susan, I don't think there would be a difference in a spring frost and a fall frost. I think the difference would be in the size and hardiness of the plants. If the plants were just recently transplanted they would be more vulnerable I think. If the plants had been in the garden for awhile and mature, they may be better able to handle a light frost. They may have damage, but it wouldn't kill them.

A hard freeze on the other hand, would be a different story.

Got it!! :)

Thanks, Susan - found and saved the article. Now if I can just remember that I did it when the appropriate time rolls around!

Marty