Plants Prepare for Extreme Cold

.Plants are adapted to specific climates and environmental regions, and some are more tolerant of cold temperatures than others. Cold hardy plants are genetically programmed to have the physiological adaptations to cope with a cold environment. This is why you generally won’t find tropical plants growing outside in the northern states. It may seem odd that a light frost in late spring or early fall can be detrimental to a tree, when the same tree will survive unscathed through winter freezes well below zero. This is because cold hardy plants acclimate to freezing temperatures well before this winter quiescence begins.

There are various degrees to which plants are cold hardy and various methods they use to achieve that hardiness. All of these adaptations are based upon some type of metabolic preconditioning. Why do freezing temperatures damage plants? Ice formation, not low temperatures, is what causes tissue damage within plants.

Plants are primarily composed of water, and damage occurs when a plant is not cold-acclimated. Ice crystals form within the protoplasts causing intercellular damage that ruptures the cell walls. This can lead to further damage to vital tissue involved with translocation of nutrients and water, resulting in potential losses of shoots, roots, or the entire plant.

This type of injury is generally first noticed on the leaves and stems, which may turn brownish-black and become mushy. Also, freezing damage to cells can create entry sites for pathogenic infection. Black heart in fruit trees is the result of pathogen proliferation of xylem tissue after freezing injury. This type of damage generally occurs to non-hardy plants when exposed to freezing temperatures, as well as cold hardy plants exposed to freezing temperatures before acclimation (as in the case of early fall frost) or after deacclimation (late spring frost after a warm period) occurs.

The spring frosts can do potential damage to new succulent growth as well as flower buds critical to fruit production. So what exactly occurs in the acclimation process to protect plants from freezing temperatures?

Tolerance of extracellular freezing is a major survival mechanism of woody plants to sub-freezing temperatures, which is exhibited by the hardiest species. In this case, water is moved outside of cells to air spaces between cells where ice will gradually form. Plants that have larger air spaces will typically survive lower temperatures. As water moves out of the cells, the increased solute concentration (from
increased sugar content) will help maintain turgor pressure to avoid collapse of the cell membrane. Those plants with thick cell walls cannot collapse and are thus damaged by formation of ice. The increase in solute concentration along with the removal of water from within the cell will also decrease the freezing temperature. The presence of dissolved solutes in the cell will lower the nucleating point of water, which is the point at which ice forms. Conversely, the nearly pure water that has been pumped out of the cell into the intracellular airspace will readily freeze under optimal conditions.

The level of hardiness that plants achieve is based upon their genetic disposition and the environmental conditions leading up to dormancy and subfreezing conditions. If all conditions are right, many plants can be tolerant to temperatures not suitable for most of us. The two main signals for initiating dormancy are photoperiod and reduced temperatures. Generally, cold acclimation occurs first in terminal buds, and is subsequently the first location to deacclimate as well. Damage to this plant tissue will generally occur in the early spring or late winter if
warm temperatures are followed by a freezing episode. Other plant tissue is more apt to be damaged in the fall if an early freeze occurs before the tissue has acclimated.

Preparation for Winter
Nurseries Can Reduce Winter Damage

Although the cold acclimation process of plants is largely predetermined by genetics and environmental conditions, there are a number of cultural practices that can be carried out before winter arrives to help prepare nursery and landscape plants for the upcoming winter (see Cultural Practices for Hardening Off).

Plants will have the best chance in over wintering with a properly balanced nutrition. High levels of nitrogen late in the growing season can cause hardening off. It is best to withhold nitrogen applications about six weeks before the first frost. An increase in the proportion of potassium in the fertilizer at this time has been known to aid in plant material hardening off. The potassium works on a cellular level in the translocation of water during these various degrees of cold acclimation. Once the plant material is fully dormant a one-time application of a balanced fertilizer does provide a significant benefit to the plant. This will provide some nutrients in the root zone, thus giving the plants a head start in the spring.

Heavy pruning late in the season can also stimulate bud break and result in a flush of new growth, and if done too late, will reduce the chances of thoroughly hardening off in time for freezing temperatures. If late season pruning is required, it is generally best to wait until late in the winter, but before the plant has deacclimated. Keep in mind some plants will ‘bleed’ if pruned in the dormant season, so it is best to find out specific plant requirements. But in general, avoid heavy late season pruning.

The amount of watering should also be reduced in the weeks prior to winter. Too much water can result in succulent growth that may not fully harden off. Plants do need to have an ample supply of water in the root zone during the winter to reduce winter desiccation, so irrigation after dormancy has been induced may be necessary if the natural conditions aren’t providing enough moisture.

Genetics will determine the capacity at which a plant can tolerate cold temperatures. Cold hardiness is a complex process, but if the correct plant material is used, then you are well on your way to a successful product. It is best to match plant material with the conditions at which you will be utilizing. Lawyer Nursery grows a wide variety of species with various levels of cold hardiness. We pride ourselves in careful selection of seed sources to ensure optimal growth in cold regions.

Cultural Practices for Hardening Off Nursery Stock:
• Make sure to use plant material hardy to your cold hardiness zone.
• Reduce fertilizer applications six weeks before average first frost date.
• Reduce N applications further and increase proportion of K in fertilizer mix.
• After a plant is completely dormant, an application of a balanced fertilizer is important for a jumpstart in the spring.
• Reduce irrigation frequency and amounts to reduce succulent growth.
• Maintain soil moisture during winter to reduce desiccation.
• Avoid heavy pruning.

Additional Steps For Containerized Plants:
• Remove plants from shade and expose to full sun. May need to be done gradually to reduce instances of sunburn.
• Mulch or insulate containers. Containers can be spaced pot-to-pot as an alternative.

High Elevations or High Latitudes
Cold Tolerance in the Extreme

Landscaping at high elevations presents many challenges. High UV exposure, strong winds, wide and sudden swings in temperature, frost and cold during an already short growing season, and heavy snow load are just a few of the many stresses plants must be able to withstand.
The exact elevation at which a plant will grow is highly dependant on local conditions such as latitude often the biggest determinant, aspect and atmospheric pressure just to name a few.

With proper care, many alpine native plants can be successfully grown at much lower elevations thus extending their range adding a unique touch to the landscape. Partial shading and careful watering during hot spells is most of what several alpine natives need to succeed in lower gardens. Many plants native to lower elevations have proven successful higher up adding much appreciated diversity to alpine landscapes.
The following chart lists tree species at Lawyer Nursery that will grow successfully to at least 7500 feet.

Where Have All the Apples Gone?
... seedling apples to bank on

Suggesting that seedling apple trees have merit for fruit production is like claiming the world is flat. Recognizing the importance of genetic diversity in the global ecosystem, bigger is not always better in regards to fruit quality. Variety (no pun intended) in fruit selection is the spice of culinary life.

As strange as it may seem, we see business opportunities to sell and disperse seedling apple trees to the American garden and countryside. This can bring pleasure to countless people, wild critters and future generations

Opportunities start with our production, and move beyond our nursery gate to retail nurseries, conservation and landscape projects. We will share some background and a few ideas that we hope will catch the attention of those looking for opportunity to do good and make a buck.

Apples, as we Americans eat them, are the result of 4.3 million years of evolution and modern breeding programs. Breeding has imparted great eye appeal, size, color, extended storage capability, but only tolerable taste and culinary appeal. Most modern commercial apples, to quote world famous gastronomic restaurateur Alice Waters, are "Farmer’s . . . quest for the reddest, most visually flawless fruit (that) has led to a flavor-deficient cardboard copy of an apple, . . . "

The origin of the apple is in Central Asia in the Tian Shan Mtns, of modern Kazakhstan. The ancestor of our domesticated apple, Malus domestica, is Malus sieversii. In the past, Lawyer Nursery has imported seed of this historic specie from Kazakhstan. A member of our staff has walked among the trees in the forests where the dominant species is Malus sieversii . These indigenous trees yield fruits varying in size from gum drops to softballs, and in color from green to yellow to red to purple.

The route of edible apples to America came through Europe, although it was the Chinese that invented grafting and true domestication sometime in the second millennium B.C. European varieties in early colonial America didn’t do well and were soon overtaken by seedlings or pippins. These eventually became widely dispersed, reverting tosexual reproduction. In time new varieties such as Newton Pippins, Baldwins, Golden Russets and Jonathans resulted, which were adapted to the conditions of North America. But the most famous varieties that are still with us today are the Red and Golden Delicious and McIntosh. (Grannyh was discovered in Australia in 1868).

Today, of course, we have modern varieties each with their own specific traits based on where it will be grown and its commercial usage.

We cannot discuss apples without mentioning John Chapman, most famously know as Johnny Appleseed. Chapman’s seedlings sold for 6.5 cents each. Stories and lore about Chapman abound, but it is safe to say he was the earliest nurseryman both famous in his own time and
remaining so today.

Lawyer Has Dispersed More Apple Seed Than Johnny Apple Seed.

We must mention here, our claim at Lawyer Nursery, that we have dispersed far more apple seed than Johnny Appleseed. Our recent estimate is that in the 50 years since our founding we have either planted or sold at least 15,000 lbs of apple seed. This is enough seed to grow 300,000,000 seedlings. This includes both US sources and imported seed.

There are about 17,000 apple varieties nurtured and named over the last 400 years. In the early 1900’s USDA cataloged over 7,000 named varieties. Since then 85% of these have been “lost” from nursery catalogs, commercial orchards, farmer’s markets and all but a few from the American table.

The fruit quality and size of seedling apples is very diverse due to hetrozygosity or extreme genetic diversity. One mature tree, will in effect, produce several thousand new varieties per year. Commercial growers look on this diversity with disdain, giving a bad rap in America, to the resulting fruit. The fact is we have “lost” one of nature’s most interesting culinary offerings from our diet.

Breeders can demonstrate the capability of producing monster apples, that only one is required to fill a pie. However, size, and visual appeal do not necessarily go hand-in-hand with flavor and texture. In Europe and Central Asia, smaller, more flavorful, and somewhat “wild” apples remain in widespread favor.

We at Lawyer Nursery, with some trepidation, suggest that there are possible business opportunities in the nursery trade in offering apple seedlings for fruit production. We do not remotely suggest that the production would be large scale and commercial. Rather we foresee other contributions to our world and a few brief examples are mentioned below. Nurserymen, landscapers, garden centers, conservationists, and small farmers, all have a business opportunity to capitalize on capturing the public’s interest in the interesting culinary merits. They can also provide nvironmental rewards, by establishing widely dispersed plantings of seedling apple trees.

Here are some fresh ideas.

Garden centers can promote and sell, or give away for promotions, small seedling apple trees. The cost is minimal both to the business and gardener. However, it would be important for the consumer to be informed on the genetic diversity and what this means in terms of expected fruit size, fruit quality and so on.

Landscape designers can consider specifying seedlings for a fruiting apple hedge or a large specimen tree in the appropriate setting, giving natural appeal with both profuse blooms and “wild apples.”

Conservation plantings already do include, in some cases, fruiting apples. However, the plants have usually been selected for cold hardiness, e.g. Malus baccata, for spring blooms rather than the possibility of providing edible fruit for wildlife and people. (At Lawyer Nursery we can attest to the fact that the bears love our apples.)

Think of America’s Blue Highways, parks, urban nature trails, picnic areas, windbreaks, rest stops, fishing access sites, wildlife viewing areas, and so on; all with the occasional seedling apple tree. In some cases it won’t be new, just better planned. An intentionally planted tree is better than one resulting from someone’s apple core being carelessly pitched out of their car’s window.

The accompanying photoshows the range of fruit size collected from three seedling apple trees naturalized along the public roads between Plains and Lawyer Nursery. As one can see two of the three trees have decent fruit for eating fresh.