Eucalyptus Cold Damage: Can Eucalyptus Trees Survive Cold Temperatures
There are over 700 species of Eucalyptus, most of which are native to Australia, with a few in New Guinea and Indonesia. As such, the plants are suited for warmer regions of the globe and eucalyptus cold damage in trees grown in cooler zones is a common problem.
Some varieties are more cold hardy than others, and eucalyptus cold protection can help the plants sustain less damage. Even if you choose a hardy specimen and protect it, however, you should still know how to fix cold damaged eucalyptus since weather can be surprising. Winter damage in eucalyptus can be mild or severe and needs to be triaged before treatment.
Recognizing Eucalyptus Cold Damage
The scent of the volatile oils in eucalyptus is unmistakable. These tropical to semi-tropical trees and shrubs are not used to freezing temperatures, which can cause considerable damage. The plants are adapted to moderate climates with little temperature fluctuation. Even endemic plants that grow where it snows are protected from huge spikes in temperature and hibernate under the snow until the growing season. Plants that experience big jumps or lows in temperature can be threatened with winter damage in eucalyptus. This occurs in regions like the eastern to central United States.
Often, cold damage isn’t recognizable until the thaw arrives. At this time you may begin to see blackened twigs and stems, rotten spots, broken plant material from heavy snow, and entire areas of the tree that are not leafing out. This indicates moderate to severe cold damage.
In mature trees, the worst you may see will be a loss of leaves after a cold snap, but sustained cold followed by mild weather will cause dead stems and possible rot. Young plants have the worst time with cold periods, as they have not established a strong enough root zone and bark and stems are still tender. It is possible that the entire plant will be lost if the cold snap was long and cold enough.
Can Eucalyptus Survive Cold?
There are several factors that affect eucalyptus cold hardiness. First is the species cold hardiness as designated by the USDA or Sunset zones. The second is the seed provenance or where the seed was collected. Seed collected at higher elevations will pass on the trait of greater cold hardiness than those collected at lower zones.
The type of freeze can indicate the hardiness as well. Plants that experience freezes with no snow cover and brisk winds desiccate and have root zone damage. Plants where heavy snow makes a blanket over the root zone and have minimal wind will have a greater chance of survival. Location, location, location. The site for the plant can help provide shelter for the plant and increase survival and vigor.
So can eucalyptus survive cold? As you can see, this is a complex question and needs to be looked at from many sides and factors.
How to Fix Eucalyptus Cold Damage
Wait until spring and then cut off any damage or dead material. Double check to make sure the stems are dead with a “scratch test,” where you make a small wound or scratch in the bark to check for life underneath.
Avoid radical pruning of eucalyptus, but once dead and broken material are removed, fertilize the plant and give it plenty of water over the growing season. In most cases, it will survive but you should think about eucalyptus cold protection for the next season.
Preventing Winter Damage in Eucalyptus
If you haven’t already sited the plant in a sheltered area, you may want to think about moving it. Place the plant in a lea, the least windy side of a building and away from scorching winter sun. Place mulch thickly around the root zone with organic material, such as bark or straw. In areas with minimal wind, site the plant with an eastward exposure where daylight will warm the plant up after a freeze.
Build a cold proof structure over the plant. Erect a scaffold and use a blanket, plastic or other cover to insulate the plant. You can even run Christmas lights under the cover to increase the ambient temperature and provide eucalyptus cold protection.
How to deal with winter damage to shrubs….
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Here in the South East (of England), we’re assessing the winter damage to our gardens.
The real problems weren’t caused by the snow, freezing winds or low temperatures of late February.
Snow and ice in early March here in the Middlesized Garden. It followed a period of warm weather, when this lavender sent up tiny new shoots.
Lucy Adams, Head Gardener of Doddington Place Gardens, told me that the real issue was the week of warm weather at the beginning of March, just before low temperatures, snow, ice and wind returned. Sap started rising and shrubs started budding.
When the bad weather hit, the plants were much more vulnerable than they would have been a month earlier. ‘The temperature here at Doddington suddenly went down to minus 14 (centigrade),’ she says. It had been around nine or ten degrees the week before.
#110 Taking Care of Frost Damaged Yards
WHAT TO DO AFTER A SEVERE FREEZE
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Faced with a yard full of frost damaged plants, often the first impulse of the gardener or homeowner is to start pruning, removing and replacing. Unfortunately, even in the aftermath of a light freeze, this is not the best course of action. After a hard freeze the results can be catastrophic.
Any plant that is still alive will attempt to recover from freeze damage. The threshold of absolute damage (death) will be different individually and of course for each species. Be assured that many plants that look completely dead will begin to recover when the weather warms up. The method of recovery and resulting appearance will not always match our idea of how the plant should look or behave in our gardens. Many plants will have lost all their woody parts, but will begin to re-grow from root or stem tissue. This is normal and typical recovery process for the plant. However, the temporary appearance of the landscape may not be acceptable to some gardeners. This means that each site will have to be evaluated. Do you let the plants recover in their own way or time or replace them with already vigorously growing (and pleasingly shaped) specimens? This decision will be particularly difficult with cassias, eucalyptus, acacias, African Sumacs or California Peppers.(top)
PRUNING OF FROST DAMAGED MATERIAL:
The extent of damage will not be apparent until re-growth starts in warm weather. While initial damage estimates can be made by observing foliage, tissue rigidity or stem flexibility, many plants are still in the process of realizing damage inflicted by the freeze. In some cases, root systems or circulatory damage is not yet apparent. Some of the plants so damaged may show no outward signs until heat or other stress causes the plant to collapse. What this means to you is that pruning should be delayed in all cases where frost damage is apparent (including discoloration). When growth resumes in the spring, you will easily see which stems or branches are not recovering fully. By the beginning of March, many plants, like Mock Orange, Photinia, Privet and Texas Ranger Sage will leaf out and show generally good recovery. Species like eucalyptus and African Sumac probably won’t show any signs of re-growth until April or May. Replacement and/or pruning decisions might need to be delayed until May, unless the decision to replace these plants with other species has already been made.
Palms and other monocot plants such as yuccas, tuberous tropical lilies, irises and some grasses are particularly prone to damage through pruning, because their method of re-sprouting is so different from other plants. The palms are particularly vulnerable because they have only one growing point, called the heart-bud. If this heart-bud is damaged, palms are incapable of manufacturing a new one. Exceptions are clumping palms such as the Mediterranean Fan Palm, or tropical branching palms, not grown here. This is why it is critical to not prune palms until active growth resumes. Any additional stress on the heart-bud, or the removal of the insulating thatch (dead leaves) could cause the palm to die. Most palm varieties growing here have not undergone weather colder than ours any place else in the world they are grown, so data on recovery is spotty. Since we know that nothing active can be done to help the palm, a course of nonintervention is strongly indicated. The Mediterranean Fan Palm may respond to the freeze by sending up many new shoots from the base. When they appear, they can be retained or removed as the owner wishes. Generally, no pruning should be done on any palms until at least five strong new leaves are visible.
After the catastrophic freeze of December 1990, inspections of local palms conducted early the following March showed a large number with strong signs of recovery. The majority of these palms that were over six feet tall and in the ground for over a year did in fact recover. Some problems developed with fungus in the crowns of freeze-damaged palms. If you suspect this, or wish to prevent it, treat the crown with a drench of copper-based fungicide.(top)
Olives damaged by a freeze can be pruned beginning in March. Pruning should consist mainly of removing twiggy secondary growth, while allowing scaffold branches to remain. Olives pruned in this manner should show a generally strong recovery by mid-summer. Don’t spray fruit-inhibiting chemicals on trees noticeably damaged by a freeze. Most of these chemicals also have growth-inhibiting properties, which can keep the tree from re-sprouting new leaves and shoots. Fruit is not expected on the majority of trees since most flower buds were destroyed by the freeze. Some trees will be undamaged by the freeze. These can be sprayed normally.(top)
EUCALYPTUS AND AFRICAN SUMACS:
Part of the problem with these trees is their inability to re-sprout well from freeze-damaged branches. Wood loss on these trees will range from minor to total depending upon age, size, exposure and growing conditions. By May you will have a clearer picture of damage, but even then the long-term effects may not be evident. Homeowners may want to evaluate the trees for extent of damage, importance of the tree to the landscape and emotional attachment then weigh replacement with better suited species. Most Eucalyptus and Sumac trees re-sprout from the roots and many will re-grow to 6 feet in one growing season. The choice, of course, is yours.(top)
Ground cover plantings Like Hearts and Flowers, Gazania and Australian Racer will have to be individually evaluated. In some cases they will be damaged enough to warrant replacement. Decisions on this will have to be based on individual economics, timing and aesthetic factors.(top)
Most Fescue lawns are made dormant by extremely cold weather. Those that have not revived by mid March should be thoroughly raked to remove thatch and then fed with a high nitrogen fertilizer such as WinterGem® or Nitra King®. Thatching lawns before fertilizing will remove dead grass and improve water and fertilizer penetration. The following procedures should be used when applying fertilizer:(top)
• Wet lawn thoroughly. Make sure ground is thoroughly soaked to a depth of 3-4 inches.
• Apply fertilizer according to package instructions.
• Water thoroughly so fertilizer disperses throughout wet soil.
• Avoid using Weed-and-Feed formulations at this time. The chemicals used for weed control will have a damaging effect on ornamental plants in and near lawns.
• Bermuda lawns should be treated normally. Bluegrass should be treated the same as fescue for recovery purposes.
• Stressed plants in lawns should have an area free of grass around their bases. This will help protect them from lawn fertilizers and is generally healthier for the plants even under normal circumstances.
Plants damaged by freezing should not be fertilized until active growth resumes in the spring. The loss of growing tissue and leaves experienced by most freeze or frost damaged plants inhibits their ability to metabolize and use fertilizers. In some cases, depending on soil chemistry and plant tolerances, more damage could result from improper and over-zealous fertilization. This is again critical for palms, which should not be fertilized until hot weather in June or July, and again in August or early September.
When fertilizing does take place, caution should be used, taking into account the compromised state of many plants. Probably the most effective fertilizers will be those which are balanced and which have a low analysis (9-9-9 or below), and those which are organically based like Star Nursery’s Dr. Q’s® Fertilizers, or traditional fish emulsion. To help soil microorganisms re-establish, homemade compost, commercially available inoculants or manufactured fertilizers with microorganisms present will be helpful. Top dressings with organic material like Dr Q’s Paydirt® or Humus-Gro will not only improve the soil, but also reduce stress on roots due to soil superheating. IN NO CASE SHOULD STRONG DOSAGES OF HIGH NITROGEN BE USED ON LANDSCAPE PLANTS following a severe freeze. Even plants with no apparent damage can be disturbed by rapid growth caused by excessive nitrogen.(top)
Proper watering of damaged plants is vital. While moist soil is necessary in almost all cases to avoid further damage from drying winds, plants which have had foliar damage or root damage have a compromised ability to make use of soil moisture. This means that the watering regime must be carefully watched, and the soil watered only when it begins to dry significantly. Doing otherwise will result in root rot and further losses. The reduced soil evaporation rate in cool weather combined with reduced demand from damaged plants indicates watering no more than once a week. Lawns should do quite well in cold weather with approximately 10 minutes once a week, or even less. Even with these guidelines, you should watch and adjust watering schedules according to prevailing conditions. Over watering at this time would be devastating to plants that have been significantly damaged by a severe freeze(top)
conservatism is called for in all gardening and landscaping activities. Too much water, fertilizer or pruning could be very detrimental and could cause much more loss than might be experienced otherwise. It is comforting to know that not doing anything at all except watering appropriately, at least until growth resumes in the spring, is the course of action least likely to cause damage. While the prospect of facing a devastated yard for many more weeks is disturbing, facing costs of a full landscape replacement because of impatience and improper maintenance is even more disturbing. Read our Gardening Tip #1045 (Pruning After Frost Damage) for more information and make full use of local resources such as the University Cooperative Extension, State Department of Agriculture, UNLV Arboretum, the Springs Preserve and your local Star Nursery. Remember, replacing in haste will waste plants and money!(top)
EucalyptusEucalyptus pauciflora ssp. debeuzevillei
Cold hardy species for the PNW
Eucalyptus are very unique trees and there are several things you should consider before planting. First, you must be prepared for them to grow explosively fast. Soils in Australia are very old and poor. Eucalyptus are adapted to these conditions. Even unamended soils in our region are richer in nutrients in comparison to native Australian soil. Rich soil combined with ample moisture results in Eucalyptus that thrive with little assistance from the gardener. Plant them in unamended soil and irrigate steadily through the first dry summer. In subsequent years it will be completely drought tolerant. They grow in a variety of soils, including heavy clay. Give them room to grow- this means plan ahead. They can grow up to 6’ a year. This rapid growth can leave trees susceptible to strong winter winds and combined with wet soil leave them vulnerable to wind rock. To avoid this do not amend the soil or fertilize. If growth is proceeding rapidly you may not water at all. Hardy Eucalyptus are for the most part very drought tolerant. They also tolerate regular irrigation (especially the water loving species E. parvula). Only stake plants less than 3′ tall- from that height on let it form its own sturdy trunk or trunks. Eucalyptus are completely intolerant of shade in our climate. Give them at least 6 hours a day of full sun in an open exposure for the strongest growth and sturdiest trunks.
For certain species- but not the Snow gums- unstable trees may be cut back by 1/3rd after the first season in the ground. This will ensure that top growth to root growth ratio is proportional and this will eliminate the threat of rocking.
All of the species that we grow have displayed excellent, LONG TERM survival in Western Oregon. That means that they will not be killed – or even injured in the harshest winters. That having been said there is no true arctic air in Australia. These trees are native to the naturally coldest locations in Australia, high elevations and frosty mountain valleys where winter temperatures are the same or much colder than our own. But topsy turvy freezes early and late can cause more damage and I have yet to find a Eucalyptus that will endure subzero temperatures as a tree. Several have resprouted from subzero lows but none have retained top growth. There are many Eucalyptus that will live and grow prodigiously in our climate for a few years- and they can achieve serious height, only to freeze completely to the ground or die in a colder than average winter. This is not a good way to go. Its expensive, dangerous and a royal pain in the ass to deal with a suddenly dead tree. Many of these borderline species will resprout if you are lucky but we don’t recommend this for the average gardener. Fully hardy, carefree species are what we promote.
For cut foliage:
Many Eucalyptus species have striking juvenile foliage that will turn to adult foliage with a much different look as they grow into arboreal form. The most familiar juvenile foliage is perfoliate which is the popular cut material of the florist trade. To retain this attractive juvenile foliage (or just to limit size) Eucalyptus may be cut back to the ground. “Coppicing” as this is called will result in a shrub that re-grows with multiple trunks.
This can also happen when a tree freezes to the ground and is possibly an adaptation to regeneration after bush fires. In Australia Eucalyptus with this form are called Mallees (pronounced Mollies). To achieve this it is best that you allow at least one to two years for the tree to establish a large root system. Coppicing is ideally done between March 1st and April 15th. This gives the tree a long growing season to reestablish new growth before the following winter. It may seem extreme at the time, when you find yourself staring at stumps, but new growth will begin in four to six weeks. Be patient. Once they start to re-grow it proceeds rapidly.
Snow gums the most cold hardy and reliable Eucalyptus in our region can NOT be coppiced for cut foliage. They have adult foliage from the get go and do not resprout from the base if cut. The individual plant descriptions will mention if this method if it is possible for each species.
Climate Adapted Plants for Gardeners in the PNW
IMHO, any kind of "topping" will either result in an ugly looking tree or a distorted and un-naturally thick crown (which you still won't be able to see through as soon as it grows back---or both. I have heard that some professional arborists supposedly have a growth retardant that can be applied to cut surfaces that MIGHT help. think your best bet is to consult a certified arborist (not a "tree trimmer) and see if they can perhaps carefully THIN the crowns out (NOT cut back) or some other treatment that will keep you, your neighbor, and the trees happy. BTW, most eucs come back strongly after being cut to the stump and a potentially very dense multi-stemmed large shrub/small tree can be created (and also maintained) in a rather short time without having to completely remove the trees. might ask whatever "expert" you get about that possible option. good luck. hope this helps a little.
Ken_adrian Adrian MI cold Z5
if you make cuts on a tree. never put anything on the cut .
you can not stop a tree from growing.. except by killing it .
and with no insult to the root mass. topping it.. will not slow it down for long .
pay to have the removed.. and pay for replacements .
Prevention tactics can minimize shock danger to new transplants. Transplant perennials and woody plants in late winter when they are still dormant so they will recover quickly with their first flush of spring growth. When transplanting seedlings, harden them off in a protected outdoor area for one week prior to transplanting so they become accustomed to outdoor conditions. Transplanting on cloudy days or in the evening gives the roots some time to recover before they are subjected to the stress of intense sunshine.
Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.