Cultural Disease
Watering
Over watering and poor drainage are one of the most common causes of poor plant health in our area, as we have heavy clay soil, which does not allow good drainage. If there is no oxygen in the soil, in the form of air between soil particles, roots rot takes place and can no longer supply the plant with moisture, so plants wilt and die. Probably the single most important component of soil is oxygen! It is important to assess the area for soil moisture and drainage before planting. Some trees, such as birch and willow, need a great deal of soil moisture; some, such as spruce and mountain ash, cannot tolerate it and will die in constantly wet soil.
To ensure proper watering, water must penetrate to the depth of the root ball. It’s unfortunately common to have underground sprinklers which go on every day for ten minutes, whether necessary or not, which usually does not give the plant's roots sufficient water, but is assumed to be consistent watering. Depth of water necessary depends on the depth of the root system - a lawn does not need watering as deeply as a mature birch tree. It will need it more often, but a good, deep watering only when needed is much better than frequent sprinkling.
How well plants recover from drought depends on the root system. A plant with a thick, fleshy root can often recover because the root can shrivel somewhat, then absorb water when it is available. A plant with a very fine, hair-like root often reacts very poorly to drought. The fine roots shrivel quickly, and cannot recover - they die. Once a plant's roots no longer absorb water, the top of the plant cannot survive.
Temperature Extremes
Temperature extremes are common in Calgary. Usually consistent temperatures at the appropriate times in the season are not stressful if the plant is hardy to the area and in an appropriate place (shade loving plants will have even more trouble with high temperatures if in too much sun). Problems arise when sudden temperature changes occur that alter a plant's normal growing cycle. Our chinooks can cause a plant that is dormant and tolerating cold well to become warm enough to break dormancy in the winter. When it gets cold again, the plant cannot go back to being dormant again and is now too tender to survive temperatures that previously caused no harm.
Plants normally become dormant in the fall in relation to day length. A plant that becomes dormant when the day is shorter than the night, if so it can handle a good frost. Unusually long, warm fall weather can trick a plant that is 'programmed' to become dormant in plenty of time to be ready for winter into delayed dormancy and frost damage.
Late spring frosts that would do no harm when a plant is dormant will kill emerging buds and leaves. Often this means no fruit on apples, Nanking cherries, Mountain Ash and Lilac that form flower buds the fall before. Plants that flower on new wood (e.g. most roses, pink-flowering spireas, potentilla) will not be affected as long as there is healthy new growth. Young leaves that are killed are usually replaced with a second set a few weeks later, but on an occasion when the second leaves of Mayday trees are also killed by frost, the third set will be very small. In this case it is possible that the tree will not survive the following winter. The tree used so much energy producing three sets of leaves that they could not survive a relatively mild winter.
Alternate freezing and thawing, often on the sunny side of trees with soft bark, such as Mountain Ash, Amur chokecherry and Mayday, cause frost cracks. The sun alternately warms the bark during the day, then it becomes cold at night, and the bark eventually cracks. This isn't necessarily harmful at the time, but bacteria can easily enter the tree at this point and cause cankers. Wounds should be left open - exposed, dry wood rarely becomes infected. Covering the area with pruning paint or sealing it with home remedies traps any bacteria and fungi inside, and gives them a perfectly protected place to grow.
Humidity is more important to some trees than others. Cedars grow best where there is high humidity in the winter, so they suffer in our dry winters. Pyramidal junipers grow in the mountains, so are much more tolerant of our climate.
Sun reflecting off snow can cause browning of evergreens on the sunny side. New growth is usually OK. It can be controlled by placing a windscreen of burlap stretched between stakes out 18-24" from the tree on the sunny side before winter sets in. Do not wrap - it creates a greenhouse effect when warm air is trapped inside on sunny days. The next very cold weather causes even more damage.
Chemical Damage
Chemical damage can be contact or systemic. It can come from sprays onto leaves, from soil into roots or occasionally from wounds in bark. Chemicals can be contact, killing the part of the plant they touch, such as weed killers that top-kill only, or systemic, moving within the plant with the sap, such as soil sterilizers.
While one expects herbicides to kill, insecticides can also kill when used at the wrong time, temperature, or on a plant that cannot tolerate it. This why it is always important to read the label before using any chemical.
Chemical damage can often be determined by leaf damage patterns. Spray damage will leave a pattern of spots equally spaced on the leaves. It can be all over the tree or only on one side of a tree, for example as a result of spray drift from lawn weed killer being sprayed on a windy day.
Chemical damage from roots usually causes black or dark brown blotches in the leaf material between the veins and around the edges - the most sensitive areas for leaf damage. This can also be overall, from a chemical in the soil around that plant's roots, or one-sided, from the root of a tree reaching an area where the chemical was used.
Cat urine is another cause of chemical soil contamination in flowerbeds on the warm side of a house in the winter.
Chemicals can also cause specific damage which must be known to be recognized, such as the very pale, almost white, needles or leaves, caused by the sterilant Atropel, or the typical twisting and distortion of new growth on tomatoes and potatoes caused by 2,4-D, which may have no affect on any other vegetables in the garden.
Physical Damage
Physical damage includes that done by birds, animals, machinery, hail, ice or heavy snow, wind, lightning and, of course, insects. Animals can eat tender growth any time of year, but damage is more common when they are lacking their normal food like in winter when there is heavy snowfall, or during a very hot, dry summer when their food is dying from drought and yours is being watered and so succulent. Sapsuckers make square holes in a square pattern in tree bark, looking for insects and enjoying the sap. Leaf cutter bees remove perfectly circular holes from roses. Deer, rabbits, porcupines, ground squirrels, pocket gophers and squirrels are common in this area. Animals such as cats can also scratch bark, disrupting patterns of water movement up a tree, and leaving open wounds that can become infected with bacteria or fungus. There are various ways to deter animals; chemicals that have specific odours repellent to certain animals and those that taste bad, avoiding plants that are known to be susceptible to animal damage in the area, fences, prickly ground cover such as raspberry canes or juniper branches in the fall over sunny beds where cats go in the winter, gopher traps, gas sticks for gopher tunnels, (remembering poisoning is illegal in the city) soap chunks in nylon stocking toes or onion bags hung at deer nose height in evergreen trees, soap chips scattered in beds where bulbs are emerging in the spring. None are guaranteed.
Machinery, most often lawnmowers or edgers, also damages bark, and cultivating around the roots of trees can cause root damage and create an entry for root rot fungus. Adding more than a small amount of soil over the roots of a tree can reduce the amount of oxygen available to the tree roots, and also mean that the bark at the base of the tree is now underground, causing possible fungal problems from soil moisture. This also happens when a tree is planted too deeply. Hail physically damages or destroys a tree's leaves, which means less ability to photosynthesize. Because leaf reduction, from physical damage or insects, also reduces root growth, it can reduce the production of food storage for winter and result in less winter hardiness. Heavy snow and ice can weigh down branches and cause breakage. Proper pruning to avoid long, thin branches that would be easily weighed down, can control this. Wrapping with open netting, not burlap, or using rope to keep plants in a compact shape to avoid snow shelves. Lightning can cause a tree to explode or cause only slight damage. It can also cause root damage where the current entered the ground.
Nutrition and Soil pH
Nutrition and Soil pH - Plants need nutrients for growth, and the pH level of the soil in which they are growing has some bearing on which nutrients they can utilize. Generally, plants that are native here are well able to tolerate our alkali water and soil. Some even prefer it. It’s when we attempt to grow plants native to quite different climates and soils that we have challenges. Saskatoon’s are native here, blueberries aren't! Potentillas like it here, rhododendrons don't! A look at lists of plants available for planting and growing here will show that most are cultivars of natives. Most of our hardy perennials have very familiar wildflower cousins, and a large percentage of our landscape trees have native counterparts. Assuming that they are planted in growing conditions that mimic their natural habitat, they should do well. An example is Mountain ash, which grow in the mountains, in rocky, quick-draining, acidic soil with very little nutrition. Plant it in rich, organic soil, fertilize it well, and give it lots of water and it will die! In their native growing conditions, much of their nutrition comes from the decomposition of plant and animal material that returns to the soil nutrients that were the organism while it was alive. This worked fine for millions of years. Now we rarely allow dead stuff in our yards, even if it was decomposed before we saw it - everything we don't want goes to somewhere we can't see. It isn't practical to allow dead birds to decompose on our front lawns, but we can, and must, compost as much as possible. It very well could be necessary to add manufactured fertilizers to enhance the nutrients available to plants, especially since we want them to grow at their optimum rate in our short growing season, but these fertilizers are much more easily utilized by the plants when added to soil that contains added organic matter, fungi, bacteria and enzymes which help break them down into a form that the plants can use.
Plants need fertilizer when they are growing, not to make them grow, so a fertilizing program begins in the spring, as soil warms and new growth begins. It is of no benefit to fertilize a lawn to make it green until the soil warms up - look at roadways where grass on the north side of the road facing the south is green sooner than grass on the south side facing north! Plants absorb most water and dissolved nutrients at the ends of their roots, which is new growth, so fertilizer is added around the drip line, not directly around the trunk of a large tree. There are many appropriate fertilizers for flowers, vegetables, evergreens, etc. - it is not necessary to have a different one for each type of plant, but helpful to know what each type of plant needs for best results, depending on what we want from that plant. We plant carrots so we can eat the roots, so a fertilizer containing more phosphorous would be appropriate for them, and also little transplants that need roots in a hurry, to be able to withstand the strange conditions they are going to be subjected to. Lawns need a high nitrogen fertilizer to grow green leaves quickly and steadily, because we keep cutting off the ones that do grow!
Nutrient deficiencies can exist because we fail to provide the plants with enough fertilizer, use one that doesn't contain specific nutrients that a particular plant needs, or the nutrients can't be absorbed or utilized by the plant. Nutrient deficiencies are not the only reason why plant growth doesn't meet our expectations, however. Often, we assume that we have neglected to meet a plant's needs, when growing conditions that are not being met are beyond our control. If soil is too cold and wet for long periods in the spring, root vegetables do not do well, and extra fertilizer will not help. Seedlings growing in windows in the late winter grow long and spindly, with small leaves and eventually keel over. This isn't lack of fertilizer, it is lack of light - we cannot make the day longer, or the sunshine in a snowstorm! African violets don't bloom as well in the winter because they need a twelve-hour day to do it. They come from an area of Africa near the equator. A different fertilizer won't help, but many people believe it will. Try to convince them that the third fertilizer they used, in April, wasn't the answer to new blooms, the longer day was!
While nutrient deficiency isn't common in annuals, or plants only in our gardens a year or two, it can be in trees, shrubs, lawns and perennials over a period of many years. Generally, a suitable fertilizer used at regular and appropriate intervals, will meet the needs of most plants here. A water-soluble fertilizer containing micronutrients, particularly iron, such as 15-30-15, will provide for them; a single-nutrient fertilizer, such as 33-0-0 won't. Rarely is a lack of one micronutrient solely responsible for plant disease, although over-abundance of one can lead to poor absorption of another. For example many years ago, potassium nitrate was a commonly used fertilizer. Soil potassium levels became so high that plants could not absorb magnesium, so magnesium sulphate, Epsom salts, were used to increase magnesium availability. Now, we do not use potassium nitrate fertilizers, but people hear that Epsom salts are helpful. Our soil can be high in magnesium, so adding more can increase the EC, to the point of dehydrating plants. Sometimes, a lack or overabundance of a nutrient can be determined by looking at the plant. Root vegetables with exceptionally large, green tops and small roots may be growing in soil too high in nitrogen and too low in phosphorous. This is typical when lawns, heavily fertilized with nitrogen, are dug up to make a vegetable garden. Soil tests can be helpful but must be read with the knowledge of what ideal levels are. Many are programmed to indicate levels that are too low, but not those that are too high. Remember - if a little fertilizer is good, a lot isn’t better!
The pH level of Calgary soil is a direct result of our high alkali water, coming from those limestone mountains. It is difficult for some plants, particularly those that are native to areas with acidic soil, to absorb iron from alkali soil and they develop iron chlorosis. Organic matter, such as your own compost, added to the soil will help modify this somewhat, and also, has added fibre as well as bacteria, etc. Peat moss is slightly acidic, but the very fine peat moss available now is difficult to get wet when it dries, and makes soil powdery. Gypsum (calcium sulphate), added to heavy clay to help break it up, has a neutral pH, and is helpful for that purpose. Do not, of course, add lime! Changing the pH is difficult and slow, but sulphur will help reduce the pH so that the plant can absorb iron available in the soil or added to it. If a particular plant that develops iron chlorosis quickly in our soil, such as a rhododendron, simply must be here, it is easiest to collect rain water, or add an acid, such as citric acid, to the water every time you water, rather than using water from our river.
Incorrect light conditions
Incorrect light conditions, also related to incorrect air and soil temperature, can have a devastating effect on plants. Those that grow best in hot sun usually need well-drained soil and warm temperatures as well as bright, direct sunlight. The sunlight available in an older garden can change dramatically over many years - the sunny flowerbed planted with roses, yucca, and herbs can become a shade garden when the Mayday tree grows up. Sometimes we don't notice the gradual change. Shade loving plants usually prefer damp, cool soil, which is one of the reasons why ground cover plants don't do well under spruce trees. It is shady, yes, but also very dry, because water runs off the branches like an umbrella and the soil can be bone dry even after a good rain. One way to judge what light and temperature a plant needs is to find out where that plant's native growing conditions are. Plants that don't get enough sun will stretch toward the light; have small leaves and long thin stems. If they are too cool they will fail to grow. In a climate where warmth after cold stimulates plant growth, warm soil is important. Plants in too much sun will wilt and leaves can have brown edges. If a plant loses more moisture from leaves through evaporation than the roots can absorb, it wilts and dies. The temptation is to add more water, but that can create an ideal environment for root rot, and still not get water to the leaves .