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About Frost and Freeze Damage

Freezing is really bad for plumeria, but frost can do some severe damage also. One method we use is to turn the sprinklers on before sunrise and allow them to run until the frost has gone our cars. Frost damage occurs on plumeria leaves, branch tips and blooms when the sun hits the ice crystals.

The following list are some meteorological conditions that can lead to frost conditions, I hope it helps:

  • Clear skies lead to radiational cooling, allowing the greatest amount of heat to exit into the atmosphere.
  • Calm to light winds prevent stirring of the atmosphere, which allows a thin layer of super-cooled temperatures to develop at the surface. These super-cooled temperatures can be up to 10 degrees cooler than 4-5 feet above the surface, where observations are typically taken. For example, if conditions are favorable, air temperatures could be 36 F, but the air in contact with the surface could be 30 degrees or colder.
  • Cool temperatures, with some moisture, that promote ice crystal development. If the super-cooled, freezing temperatures can cool to the dew point (the temperature at which, when cooled to at constant pressure, condensation occurs; moisture will have to come out of the atmosphere as fog, frost, etc) frost could develop on exposed surfaces.
  • A local study done on frost formation relating temperature to dew point has these guidelines for frost: temperatures from 38 to 42 F can lead to patchy frost, 33 to 37 areas of frost, and 32 and below widespread frost/freeze. Note that the study did not factor in other considerations to frost, such as sky cover and wind speeds.

Local topography has a large role in determining if and where frost develops. Cold air will settle in the valleys since it is heavier than warm air, therefore frost conditions are more prone in these regions. Valleys also shelter the area from stronger winds, enhancing the potential for frost. 
Other local effects, such as soil moisture/temperature and stage of vegetation “greenness” are factors that can affect the possibility of frost forming.

If plumerias suffer frost damage from freezing temperatures, prune the damaged areas to help the plant recover.

  1. Prune as soon as possible after you seed frost of freeze damage. The Pruned tips are more fragile and can be more susceptible to cold weather and may suffer even more damage if temperatures are below freezing after they are pruned. In addition. Frost or freeze damage with show up the next day on leaves and within a few days to a week.
  2. Determine the extent of the damage. Leaves may turn brown or black and hang from the stem usually when a day or two. Stem damage appears as soft, mushy tips that may ooze a brownish fluid. Squeeze stems between your thumb and forefinger. If you feel separation of tissue inside the stem, it is damaged and should be pruned. Loss of the entire plant is possible after hard freezes.
  3. Cut damaged leaves 1/2 to 1 inch from the plant stem with sharp pruning shears, leaving a leaf stub. Never pull off damaged leaves. The leaf stubs will dry out and later fall off on their own.
  4. Prune damaged branches with sharp tools. Cut small sections off at a 45-degree angle until you see only white, woody pith at the cut. Swab cutting blades between cuts with rubbing alcohol or hydrogen peroxide to prevent introduction of bacteria into fresh cuts.
  5. I is a good idea to seal branch cuts with lime paste or latex caulk. The lime paste has a natural antifungal element in it.
  6. Do not allow the plants to dry out completely, but too much water will damage them further.
  7. Always Protect pruned plumeria from exposure to temperatures lower than 40 degrees Fahrenheit. You should always protect plumeria from freezing temps of when there is a danger of frost.
    Protect from frost or light freeze:

    1. Using plastic to cover your plants will retain the cold, if the tip touch the plastic it will damage the tips.
    2. Old Socks on the tips.
    3. Cover with frost cloth
    4. Use old style outdoor Christmas lights or outdoor light bulb under the covering. Make sure they are not LED.
  8. Freeze damage normally will not travel down the plant, but check to see how far the damage actually goes. Freeze damage will come up from the bottom of the plant.
  9. Sometimes you will need to cut all the way to the trunk. As long as you have live roots, the plumeria has a good chance of surviving. 

When temperatures drop below freezing, the latex in Plumeria freezes. Once you decide to cut the plant you need to make sure you cut to good white wood with no signs of black or brown. 

 
 

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Understanding Plumeria Dormancy

Dormancy, state of reduced metabolic activity adopted by many organisms under conditions of environmental stress or, often, as in winter, when such stressful conditions are likely to appear.

In plant physiology, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species, which enables them to survive in climates where part of the year is unsuitable for growth, such as winter or dry seasons.

Plant dormancy

In plant physiology, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species, which enables them to survive in climates where part of the year is unsuitable for growth, such as winter or dry seasons.

Innate dormancy occurs whether or not external conditions are suitable. Most plants of temperate regions, such as maples, pass through a phase of innate dormancy coinciding with an unfavorable season. But several species of annual weeds like groundsel (Senecio vulgaris), shepherd’s purse (Capsella bursa-pastoris), and chickenweed (Cerastim spp.) show imposed dormancy only in the very cold weather.

Plant species that exhibit dormancy have a biological clock that tells them to slow activity and to prepare soft tissues for a period of freezing temperatures or water shortage. This clock works through decreased temperatures, shortened photo period, or a reduction in rainfall. In higher plants, innate dormancy involves seeds, underground organs such as rhizomes, corms, or tubers, and the winter buds of woody twigs.

Seed dormancy

Plumeria seeds do not germinate as soon as they are formed and dispersed. They wait until favorable conditions are present. Thus, dormancy helps to keep the seed viable for months or even years. Plumeria seeds have been know to germinate after 10 years or more. However, the germination rate does decrease over the years.

A plumeria seed dormancy is considered to be seed coat dormancy, or external dormancy, and is caused by the presence of a hard seed covering or seed coat that prevents water and oxygen from reaching and activating the embryo.

Under normal conditions, the plumeria seed matures on the tree in approximately 9 months. The seeds will stay in a dormant state until they are exposed to warm temperatures and moisture. In nature after the seed pod opens the seed coat is weakened via a process called scarification by abrasion in the soil, by the action of soil microorganisms, by moisture and warm temperatures.

Causes of Dormancy

The dormant state that is induced in an organism during periods of environmental stress may be caused by a number of variables. Those of major importance in contributing to the onset of dormancy include changes in temperature and photoperiod and the availability of nutrients, water, oxygen, and carbon dioxide. In general, because organisms normally exist within a relatively narrow temperature range, temperatures above or below the limits of this range can induce dormancy in certain organisms. Temperature changes also affect such other environmental parameters as the availability of nutrients, water, and oxygen, thus providing further stimuli for dormancy. The lack of water during summer periods of drought or winter periods of freezing, as well as annual changes in the duration and intensity of light, particularly at high latitudes, are other environmental factors that can induce dormant states.

Under natural conditions, most of the environmental variables that influence dormancy are interrelated in a cyclical pattern that is either circadian or annual. Fluctuations in the major daily variables—light and temperature—can induce rhythmical changes in the metabolic activity of an organism; annual fluctuations in temperature and photoperiod can influence the availability of nutrients and water.

Since plumeria can live for many decades or even centuries they must have mechanisms in place which allow them to survive dry periods. Dormancy is a phase in development which allows y plumeria to survive these unfavorable conditions. Plumeria are tropical plants and overall cold hardiness will vary even in dormant plants, however exposure to freezing temperatures will kill a plumeria plant.

Stages of Dormancy

The development of dormancy typically occurs in phases. The first phase is termed pre-dormancy. This early phase is reversible in that if the plumeria is returned to favorable growing conditions, in a greenhouse for example, it will resume growth. As pre-dormancy develops the range of environmental conditions that allow growth to resume narrows. Following pre-dormancy if the plumeria enters true-dormancy. In true-dormancy growth will not resume even if the plant is returned to optimal growing conditions. It is believed that plumeria never enter into a true-dormancy state.The plumeria is often defoliated at this point, and a period of prolonged chilling is required before growth resumes. The final stage of dormancy is post-dormancy. This stage is typical of later winter and early spring. In post-dormancy the plumeria is capable of growing, but it is still suppressed by adverse environmental conditions (e.g. low temperatures).

Environmental Triggers

LENGTH OF DAYLIGHT – The main environmental signal which triggers the onset of dormancy is length of daylight. For most plumeria, long days promote vegetative growth and short days trigger dormancy. As days begin to get shorter in later summer growth slows, and eventually going dormant. It is actually the length of the night that is critical, not the length of the day. Short nights stimulate growth, long, uninterrupted nights stimulate dormancy. Length or daylight, of course, is a very reliable environmental signal since it is perfectly stable from year to year and plumeria will not be tricked into growing longer because of an abnormally warm fall. Length of daylight then is the primary trigger that results in the changes in growth regulator production which in turn results in dormancy development. The growth regulator abscisic acid (ABA) apparently plays a role in dormancy development and has been found to build up to high levels in the fall.

INFLUENCE OF TEMPERATURE – Decreasing temperatures also play a role in dormancy development. Short days cause the plumeria to enter pre-dormancy (and maybe even true-dormancy). It is believed by some researchers that cool temperatures are needed for the plant to enter true-dormancy. Whatever the specific case, dormancy in many plumeria develops more quickly when short days occur in combination with cool temperatures.

INFLUENCE OF WATER AND NUTRITION – Both water supply and mineral nutrition also interact with dormancy induction. Water stress deepens dormancy and will result in defoliation. High mineral nutrition can result in delaying dormancy. This is particularly true with the mineral nitrogen. High levels of nitrogen should never be given to plants in late summer or early fall since they may actually flush and resume growth. During dormancy do not fertilize and mildly water or mist stress plants only if signs of dehydration are visible.

Release from Dormancy

Some researchers believe that during short days in the fall ABA builds up to high levels and induces dormancy. Chilling may be responsible for the breaking down of ABA. Until enough hours have accumulated to remove the inhibitory effect of ABA the plumeria will not break dormancy. When the soil begins to warm, promoters of growth such as gibberellin and cytokinins build up, signaling the plumeria tips to resume growth.

Once the plumeria is in a post-dormant condition, warm temperatures and increasing day lengths are required for normal shoot expansion. Warm temperatures are probably the most critical environmental factor at this point. 

Related Images:

USDA Plant Hardiness Zone Map

USDA Plant Hardiness Zone Map

The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.  

For the first time, the map is available as an interactive GIS-based map, for which a broadband Internet connection is recommended, and as static images for those with slower Internet access. Users may also simply type in a ZIP Code and find the hardiness zone for that area.  

No posters of the USDA Plant Hardiness Zone Map have been printed. But state, regional, and national images of the map can be downloaded and printed in a variety of sizes and resolutions.  

http://planthardiness.ars.usda.gov/PHZMWeb/

all_states_halfzones_poster_300dpi

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How air temperature affects plants

Most biological processes will speed up at higher temperatures, and this can have both positive and negative effects. For example, faster growth or fruit production is one benefit, in most cases. However, the excessive respiration that occurs is adverse because it means that there is less energy for fruit development and the fruits will be smaller. Some effects are short term, while others are longer term. The plant’s assimilation balance, for example, is influenced by the temperature and is affected immediately. Flower induction, on the other hand, is determined by the climate over a much longer period.

Root zone temperature and plant health

There are many aspects of crop and plant production that are critical for the success of the effort. One of the most often overlooked and seldom allow ed for aspects of production centers around the temperature of the root zone. After all, it is out of sight and there is not much that can be done about it. Besides, it must be OK to hold the entire plant at the same temperature, right? Wrong; and here is why.