Ice Covered Stem

Those of us who live in the temperate zones i.e. those that routinely get at least one killing frost, often have to deal with injury to our landscape plants from cold temperatures. When we venture out into the garden in the early spring, we begin to see dead or damaged plants that seemed to be in good shape the previous fall. What happened?

Of course, the first thing and for some people, the only factor we think about is cold temperatures. However, there are several other weather related impacts that need to be considered.

1. Low Temperature Injury – Most gardeners are familiar with the USDA Hardiness Zone map. This divides each area of the country into units based on the typical lowest temperatures expected. For instance, if you are in USDA Zone 5, you can expect to experience winter low temperatures between -10 and -20 degrees Fahrenheit.

Plants that are not winter hardy for your Zone will suffer damage to buds, twigs, branches or, in extreme cases, the entire plant will die. Basically, this is due to the fact that the cells within the plant tissue will freeze and cause its solid cell walls to break. The dead cells will turn brown and, of course, will never return.

Desiccation on Rhododendron

2. Desiccation Injury – Cold air can hold less moisture than warm air. So, cold winds flowing over buds and other plant tissue in the winter may slowly pull moisture from the plant. Since the soil is frozen and the roots cannot replenish the moisture, the plant cells may lose all their water. This will cause death and browning of that tissue. This is especially a problem on broadleaf evergreens such as rhododendrons and boxwood.

3. Frost Cracks – When the wood on trees or shrubs is frozen but the sun shines on a January or February day, there may be enough heat generated to begin to expand the exposed bark. Since the wood beneath is unable to move, the bark may develop a split. Often, but not always, this split will be on the south or southwest side of the tree since that is the direction of the most intense winter sun.

4. Snow or Ice Damage – The weight of ice or snow may cause flexible trees such as birches or evergreens such a pines bend over. In some cases, this will be heavy enough to actually break off the branch or the entire tree. In others, however, it merely bends the plant and it will return to its formal position. Unfortunately, the bending may have cracked the bark allowing fungal organisms to enter the plant and cause the development of open wounds called cankers.

5. Salt Damage – Although special anti-icing products are now available that do not damage plants, plenty of people still use good old salt. Whether the salt is regular table salt or a granular fertilizer, it has the same effect on plants. When salt comes into contact with plant foliage or roots, it forms a powerful attraction to water. It will pull the water out of the plant tissue causing it to die and turn brown.

6. Heaving – Soils that contain a lot of clay are plagued by a process called heaving. Clay soils are poorly drained and retain too much water. During the winter, when that water freezes, it expands. This can cause damage to roots and, in some cases, may actually push plants out of the ground. The effect is greater on plants that were installed late in the fall and have not had a chance to establish enough roots.

7. Rodent Damage – Unlike bears, mice do no hibernate in the winter. Therefore, they need to continue to eat. If the winter has a lot of snow and other food sources are denied, mice may turn to chewing on the bark of trees. Often, they will burrow under the snow and much and eat the bark at the base of the tree. If they destroy enough of it, they will have girdled the tree resulting in its loss.

8. Early Spring or Early Fall Frosts – Plants that are hardy for cold winter areas have developed one or more techniques for surviving. Generally they build up hardiness slowly in the fall, reach peak hardiness in the height of winter and then slowly lose hardiness into the spring. For example, a plant buds that will survive in -20 degrees in February, may be damaged or killed by 20 degrees in October or March.

So, what can you do about all these problems? Check back next week for How to Avoid Winter Injury in Landscape Plants.

1. Low Temperature Injury – The key to avoiding this problem is to not “stretch the zone” with your plants. This means that, for instance, if you are in USDA Hardiness Zone 6, avoid using plants that are only hardy to Zone 7 or 8. You may get away with this for several years if the winters are warmer than average. However, all that it takes is one night below the “typical” low temperature for your zone and the plant may die. That is a fallacy of people when they think that global warming automatically changes their climate zone.  You may, in fact, experience above average temperatures for 364 nights but, if that one night in the dead of winter drops below the hardiness level of the plant…it will still be dead.

The other factor here is the condition of the plant coming off the previous growing season. There is some evidence that plants that were stressed by drought or excessive heat or other factors may not be able to attain their normal level of winter hardiness. Thus, even though the plant is technically hardy for a particular zone, if it comes into the winter under stress, it may still be damaged by “normal” low temperatures.

Burlap Wind Protection

2. Desiccation Injury – Generally, the key factor in desiccation injury is the type of plant and the direction of the predominate winter winds. As we mentioned before, evergreens, especially broad leaf evergreens like rhododendrons and boxwood, are most likely to sustain this type of damage. Therefore, these types of plants will benefit most from protection from winter winds. This can be done by a temporary wind shield such as burlap fences for rhododendrons and fences, buildings or other more permanent windbreaks may also be used.

Plastic Tree Wrap for Both Rodents and Frost Crack

3. Frost Cracks – Preventing the penetration of winter sunlight is the object to preventing winter cracks. Smooth, dark, young bark is most susceptible to this damage. So, on newly planted, small trees such as a maple, it might pay to wrap the bark in a light colored material that will reflect the rays of the sun. The key is to remove this wrap after a season or two and either leave it off or replace it if the bark has not yet become rough textured and more “mature”. If the wrap remains on the tree too long, the expansion of the girth of the tree may eventually cause it to cut into the bark and girdle the tree.

4. Snow or Ice Damage – First and foremost, don’t shovel the snow from your driveway or sidewalks onto the top of your landscape plants. Generally, they can handle the weight of a normal snowfall but the added snow may cause damage. If you have tall, upright arborvitae trees, you might need to tie them together with ropes in the fall  when they are older and have become very tall and weak. Gently knock off excessive snow cover as soon as the storm is over.

Wrap Left on Too Long

5. Salt Damage – If you must control the ice on sidewalks or driveways with other than mechanical means, always use products labeled as not damaging to plants. Remember that granular fertilizers are also salts and could damage nearby plants if applied excessively for ice control throughout the winter.

6. Heaving – This problem takes a little more work than some of the others. If you have clay soil, you need to incorporate large amounts of organic matter such as compost, leaf mould, clippings, etc. This will help to improve the drainage of such soils. However, this needs to be done before you install your plants. It is pretty tough…though not impossible…to amend the soil after landscape plants, other than annuals, have been put into the ground.

7. Rodent Damage – This is most commonly a problem during extremely cold winters with large amounts of snow on the ground for long periods. Since you can’t predict which winter is going to meet these criteria, you need to take some general steps. One is to avoid piling mulch up against the trunk of the tree. Often mice will burrow in the mulch right up to the tree and chew away in the comfort and security of the mulch. Also, wrapping the trunks of young trees that still have immature bark can also be a deterrent.

8. Early Spring or Early Fall Frosts – Unfortunately, on a practical level, there is not always anything you can do about this type of damage. If you have plants small enough to cover with a tarp or other covering, that can help for a night or two. However, this won’t do much for large shrubs or trees. Remember that the goal of any covering is to keep the temperature of the plant material at least one degree above that needed for the cells to freeze. Unlike animals, plants don’t “feel” the cold. Their cells either freeze and die or they do not freeze and survive. It is that simple.

Clematis ‘Barbara Harrington’

Over the years of dealing with the gardening public, I realized that we often throw around terms and names that could be a bit misleading. Eventually, I jotted some of these tricky terms down and came up with the following:

The mountain ash tree (Sorbus) may come from the mountains but it is not really an ash tree (Fraxinus). It is actually a member of the Rose Family and is a close relative to apples, pears and roses. Mountain ash trees are not bothered by the Emerald ash borer either although, since mountain ash have their own serious disease and insect problems, that might not be a bad thing.

Boxelder tree seedlings are often mistaken for poison ivy when they first emerge from the seeds. They have the same three leaf structure but they soon form a tree-like stem and not a vine like poison ivy.

Douglas fir is not a true fir tree. Kirk Douglas was the star of Sparticus.

Blackberry plants are less winter hardy than raspberries. When you pick a blackberry, the little white pit comes along with it while the pit stays on the plant when you pick a raspberry.

Dutch elm disease killed primarily American elms (Ulmus americana). It might have come to the U.S. from Holland, thus the name.

Oregon grape holly (Mahonia) is not a holly (Ilex). It may be from Oregon but it does not produce grapes either.

The roots of black walnut trees (Juglans nigra) produce a substance called juglone that is poisonous to many other plants. Tomato plants growing near walnut trees will often wilt and die in late July.

Hostas used to be called Funkia. There was a rock group called the Funkadelics back in the 1960s but I don’t think they had anything to do with hostas but might have been familiar with grass

All azaleas are actually rhododendrons. Only a small number of rhododendrons are azaleas.

Spider mites are not insects. Insects have six legs. Spiders and their relatives have eight. Eight is Enough was a television program back in the 70’s.

Staghorn sumac has red berries borne at the tips of the branch. Poison sumac has white berries borne along the stem. Chuck Berry is one of my favorite singers.

Grape hyacinth are not hyacinths. They are in the genus Muscari. Their fruit makes lousy wine.

Onions form bulbs in response to day length. Some that will grow in the North will not form bulbs in the South where day length in the summer is shorter.

Bats have their young during the first two weeks of June. The runt of the litter is always named Robin.

Yellowjackets, wasps and hornets live and use their nest just one year. A few queens survive the winter and re-establish completely new nests the following spring. The rock band, “Queen” maintains a nest in England.

As always, if you have landscape gardening questions or have a topic you would like to see covered, please let me know.

Also, I have recently published a couple of eBooks that you might want to check out. The titles are, “A Rookie’s Guide to Designing Beds and Borders” and “A Rookie’s Guide to Implementing Beds and Borders“.

I am currently working on the next eBook, “A Rookie’s Guide to Hostas, Hostas, Hostas” which should be ready by the end of November, 2012.

Seedlings of the boxelder tree (Acer negundo) have prominent “leaves of three” and are often mistaken for poison ivy.  As they grow, however, they soon form a tree-like central stem and stand upright on their own. Poison ivy (Toxicodendron radicans) is a vine and needs something upon which they can grow such as a tree trunk or fence to raise their foliage toward the sun.

Douglas fir (Pseudotsuga menziesii) is not a fir (Abies species), however, Kirk Douglas was the star of Sparticus. Douglas fir was named after the plant explorer, David Douglas. It is a tree that somewhat resembles a hemlock (Tsuga canadensis) thus the genus name, Pseudotsuga. The specific ephithet, menziesii, is in honor of another famous plant explorer, Archibald Menzies. Gee, there some of these scientific names actually do have some rhyme and reason.

Dutch elm disease killed primarily American elms (Ulmus americana). The disease is believed to have come from Holland on some veneer wood, thus the name. You would be amazed at how many people think that it attacks “Dutch” elms when there is no such thing…as far as I know, anyway.

Oregon grape holly (Mahonia aquifolium) is not a holly (Ilex species). It may be from Oregon but the purplish fruit it develops are not good for making wine…at least not in the classic sense. I know that people make wine out of all kinds of stuff including dandelion greens so who knows.

The roots of black walnut trees (Juglans nigra) form a substance called juglone that is poisonous to many other plants. Tomato plants growing near walnut trees will often wilt and die in late July. However, many other plants do not seem to be affected. For those that are impacted by juglone, the chemical gets into the roots and soon gums up the water carrying vessels. Thus, the plants start to wilt during the hottest part of the summer when water demands are greatest.

Our beloved, Hostas used to be called Funkia after a guy named Heinrich Christian Funck. There was a rock group called the Funkadelics but I don’t think they had anything to do with hostas. Hostas were also called Plantain Lily but that too has been largely abandoned by the gardening public. Today it is simply, Hosta.

All azaleas (Rhododendron species) are actually rhododendrons (Rhododendron species). Only a small number of rhododendrons are azaleas. How do you tell the difference? Heavy duty fans of the genus have several ways they use to divide the thousands of species and cultivars of rhododendrons. However, one simple delineation is that rhododendrons generally bear their flowers at the tips of their stems. Azaleas generally have flowers all along the length of the stem too.

Spider mites are not insects. Insects have six legs. Spiders and their relatives have eight. Eight is Enough was a television program back in the 70’s. Perhaps the key here is to know that many of the commonly used insecticides are aimed at…guess what…six legged creatures. They may not be effective against the eight legged critters that are sucking juices from our plants. You can learn more about insects and even help us identify some…Name That Bug.

Staghorn sumac (Rhus typhina) has red berries borne at the tips of the branch. Poison sumac (Toxicodendron vernix or Rhus vernix) has white berries borne along the stem. Chuck Berry is one of my favorite singers. Poison sumac is almost always found in wet, swampy areas while staghorn sumac is usually found in higher ground.

Grape hyacinth are not hyacinths. They are in the genus Muscari. Their fruit makes lousy wine. See Oregon grape holly above for a discussion of wine makers.

Bats have their young during the first two weeks of June. The runt of the litter is always named Robin.

Yellowjackets, wasps and hornets live just one year. Only the queens survive the winter and re-establish new nests the following spring. The rock band, “Queen” minus their wonderful, late lead singer, Freddie Mercury, maintains a nest in England.

There are literally hundreds, perhaps thousands, of cultivars of crabapples currently available. Every nursery or plant store will offer many from which to choose. So, how do you make the right choice for your landscape? The following traits should be considered when purchasing one for your yard:
Disease Resistance. Certain species of ornamental landscape plants come with a lot of “baggage” that could cause you problems in the future. One big problem is diseases. From the day you put certain plants in the ground, you can bet with a high degree of certainty that someday, they will get sick. So, the key is to do a little research before hand and AVOID future problems.

Although we make a big deal of calling these ornamental trees, crabapples, the fact is that they are just apple trees with small fruit. Therefore, they have the same range of problems as their Red Delicious or Granny Smith cousins. In the landscape, we are not so concerned with the quality of the fruit as they are in the orchard. However, crabapples disfigured by diseases can also be a big negative in certain trees in the landscape.

Like other apple trees, crabapples are susceptible to the fungal diseases called apple scab and cedar-apple rust. These diseases can disfigure the leaves and, in extreme cases, cause defoliation of the tree by mid to late summer. This is not a pretty sight. Successive years of defoliation can weaken the tree and lead to its decline. Some sort of fungicide treatment is the most common approach to combating this disease both in the landscape and the orchard.

A serious, life-threatening, bacterial disease caused fireblight also infects crabapples. This disease will kill the tips of branches in its early stages and may eventually kill the entire tree. Since it is bacterial, fungicides do not work against it and it is very difficult for the homeowner to treat.

Our goal should always be to minimize the use of pesticides in the home landscape. This is a place for beauty and nature. So, the preferred approach is to avoid these diseases by seeking out cultivars that are resistant to them.

Plant breeders work hard to select crabapple cultivars resistant to the common diseases. Resistance does not mean immunity. Resistant plants may still become infected but generally not as easily as susceptible types. If they do develop the disease, it may not be as severe.

We will cover the ornamental traits that you need to consider when selecting crabapples in the next few paragraphs. However, for the general home garden, disease resistance should trump all. Sure a certain cultivar may have magnificent flowers in May, but, if it loses all its foliage to apple scab, it will spend most of the summer looking pretty ratty.

Fruit. Crabapples develop fruit in a wide range of colors, quantity, sizes and persistence (how long they hang on the tree). These factors are important to consider especially if the tree is located over a driveway or sidewalk where they would cause a mess.

If the tree is to be located away from the house, it may be worthwhile to have a heavy fruiting cultivar that hangs onto its fruit throughout the winter. That will provide a great view from the house and any mess with the fruit will be minimized.

Also, some cultivars are “alternate bearing” which means that they produce a heavy crop one year and a small one the next. For consistent display, choose annual bearing types. Sprays are available which will “thin” the fruit from the tree but this process is dependent on proper timing and the results can vary greatly from year to year. The best control for excessive fruiting is to plant a low producing cultivar if that is what you desire for a particular location.

Flowers. Most crabapples have pinkish colored buds that open into white to pink blooms. A few darker red flowering cultivars are available but many of these are susceptible to apple scab. As with most members of the Rosaceae Family of plants, apple blossoms have five petals. Double flowering cultivars with many more petals are also available. If you have room for several crabapples, you can also choose early, mid and late season blooming cultivars to extend the season.

Foliage. Leaf color on crabapples may range from light to dark green to dark purple. Be sure the contrast between flower, leaf and fruit color is such that each trait is properly displayed.

Water Sprouts and Suckers. Water sprouts are vigorous shoots that grow straight up from branches often appear after a heavy pruning the previous season. Suckers are those annoying stems that come up from the ground at the base of the tree. Both types of growth are undesirable and certain cultivars are more prone to produce them than others.

Check on these factors before purchasing that crabapple to cut the level of maintenance and increase the level of enjoyment for years to come.