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Crimes Against Plants and How to Avoid Them
(Avoiding plant installation and maintenance problems)
You have found the perfect plant (or plants) for you landscape. Beautiful blooms, fantastic fruit, or awesome fall color – it will look great in your landscape. But you take it home and it never seems to look like the plant on the tag. From the “should be obvious” to the less apparent, crimes against plants are far too common, and frequently the cause of plant decline in the landscape. Many landscape problems can be avoided with planning, proper planting techniques, and appropriate maintenance.
Location, location, location. The first step in setting a plant up for success is choosing the right plant for the right place. Although it can be tempting to convince yourself that your backyard gets enough sun for a rose garden, planting a plant in the wrong growing environment will set it up for failure. Hardiness zone, light, soil type, space, weather exposure, and soil conditions all need to be taken into account when choosing plants for the landscape. Ignoring these factors can affect many aspects of plant growth including flowering, fullness, leaf color, and susceptibility to insects and diseases.
Hardiness zone. Plant hardiness zones are based on the average annual minimum winter temperature. It is important when selecting plants that are at the edge of your hardiness range (for example a plant that grows in zones 6-10 in zone 6) to keep in mind that winter damage can occur because temperatures will likely fall below the average, especially if this happens for an extended period. It is advisable to locate borderline-hardy plants in protected areas. Although not discussed as frequently as cold hardiness, there are also plant heat zones which are based on the number of days over 86 degrees Fahrenheit. Plant heat zones should be considered when choosing plants near the warmer part of the range (a plant that grows in zones 2-4 in zone 4). These plants may not be able to withstand higher heat well and can decline due to heat damage in hot and dry weather.
Light. The correct light exposure is important because plants have adapted to perform best in certain conditions. Incorrect conditions can impact a plant’s ability to photosynthesis, flower, and develop, and can reduce its ability to handle stress (such as direct sun for a shade plant or lack of water). Full sun plants should receive a minimum of six hours of direct sun daily, part sun 4-6 hours, and shade plants less than 4 hours. It is also important when that sun exposure occurs. Part sun and shade plants generally perform best with morning sun and afternoon shade, or filtered sun. Direct afternoon sun is generally too intense for these plants. Plants that do not receive enough sun will flower less and will be more open and less full. Shade or part shade plants in too much sun may experience leaf burn or leaf bleaching, and are likely to experience water stress more easily.
Soil type and conditions. Soils are generally classified based on the relative proportions of sand, silt, and clay they contain. The proportions of these components determine water infiltration and retention as well as soil aeration. Sandy soils have rapid drainage, poor water retention, and high aeration. Clay soils have greater water retention, drain poorly, and have fewer air spaces. An ideal soil is around 40% sand, 40% silt, and 20 % clay. The health of soil can change over time as use can lead to compaction, erosion, and depletion of soil nutrients. In many cases, soils can be amended to improve soil conditions by adding organic matter or tilled to relieve compaction. A soil test can provide information on soil nutrient levels and pH and should be done prior to fertilization or liming. Although soil can be improved, it is important not to ignore the natural conditions of the area. Acidic soil or poorly drained soils are conditions that some plants are better adapted to than others. Again, the practice of choosing the right plant for the right place helps to reduce plant stress and promotes healthier plants.
Weather exposure. Microclimates, or pockets of modified conditions, can be influenced by buildings, bodies of water, structures, and surrounding plants. Although these conditions are usually site specific, there are some general microclimates that should be considered when planting or designing a landscape. Areas with a southern exposure have the greatest sun exposure and amount of heating. Plants in these areas will likely experience greater heating in late winter and early spring, which may lead them to break dormancy earlier than other plants and putting them in greater danger for damage from spring freeze and frost events. These plants also have a greater chance of experiencing frost cracks in winter. Southern and western facing walls absorb heat which is radiated back to the surrounding plants, causing additional heating. In the summer, this may lead to earlier water stress or heat damage. Topography such as hills and slopes can be more likely to experience erosion and potentially drying winds. Low areas can be cold traps.
Space. Give you plants room to grow! Although tempting to select a plant larger than your area with the intention to keep in trimmed back, this can be an uphill battle if the plant is happy in its new home. Average and maximum plant size, growth rate, and size of the planting area should all be considered. Planting too close to a house, sidewalk, or another plant can lead to uneven growth (or pruning), additional plant stress, and can lead to a decline in plant health.
The Planting Hole. The commonly accepted guidelines are that the planting hole should be no deeper than the rootball (1-2” less than the height of the root ball is common) and no more than 2-3x as wide as the diameter of the rootball. In regards to depth, it is important not to plant too deep or too high. Problems that arise when trees and shrubs are planted too deep include root and crown rot, girdling roots, and lack of oxygen to the roots. All of these can result in slower plant growth and general lack of plant vigor. A wide planting hole is important as preparation breaks up the soil surrounding the newly installed plant, allowing for roots to extend into the native soil and become established more easily. There are lower oxygen levels in undisturbed soil, which contributes to slower root growth as roots reach the undisturbed area surrounding the planting hole.
Preparing the Plant for Success. Life during production can be stressful on plants. Container grown plants have a limited rooting area within the pot, which commonly leads to circling roots. Circling roots need to be addressed at planting or they can lead to poor establishment and girdling, which can eventually lead to plant death. Methods for dealing with circling roots include cutting the root ball at intervals using pruners or a knife, separating roots by hand, or shaving the outside of the rootball.
Balled and burlapped plants (B&B) also need attention at planting. All string or twine needs to be removed from the ball. All synthetic burlap needs to be removed and at least the upper half should be removed with natural burlap to ensure root growth isn’t inhibited. For larger plants that come with a wire basket, at least the top third of the basket should be removed.
Backfill. Backfilling is a very important part of the planting process. It is important when backfilling not to over-compact the soil. Heavy tamping, either with equipment or feet, can be very common but is not good for the plant. Heavy tamping removes all air pockets from the soil and, although large air pockets are undesirable, small pockets are needed. Light tamping is ok, but a better method for settling soil is to water thoroughly halfway through filling the hole and then again as the hole is completely filled. The hole should be backfilled with existing soil unless the soil is of very poor quality such as excessively sandy, heavy clay, or fill from new construction. If an entire planting bed is being created, performing a soil test and amending the bed with organic matter as recommended is a good practice.
Staking. Staking of trees should be as-needed, depending on the size and condition of the tree and the area that it is being planting. Large trees, trees not stable in the soil, or trees planted in windy areas need staking. Small trees generally don’t need to be staked if they are stable in the soil, since the movement or the trunk due to wind helps to create a stronger tree. Trees should generally remain staked for only 1-2 growing seasons (1 year). Not removing stakes in a timely manner can result in girdling of stems or branches or plant damage due to rubbing from the staking materials.
Good maintenance helps to ensure good establishment, which is the foundation for future plant health.
Mulch. Mulch is best applied in spring when the soil still has winter moisture. Mulch should be applied no more than 2-4” thick and should be kept away from the base of plants. When used appropriately, mulch reduces evaporation from the soil, adds organic matter to the soil (for organic mulches), acts like an insulator for plant roots (lessening the effects of fluctuating temperatures), and helps suppress weed growth. Mulch should not be piled up against plant crowns or tree bases because it can maintain moisture against the bark, leading to disease development, or can act as a home for rodents that may eat the bark or stem. Too thick a mulch layer can either stay too wet, leading to rot problems, or can prevent water from reaching the soil where it can be taken up by plants. Keep in mind that inorganic mulches such as stone or plastic don’t provide the same benefits to the soil or plants.
Watering. Adequate (but not excessive) water is essential for establishment and success of new plants. Plant water needs vary on a day to day basis and are influenced by soil type, plant size, weather conditions, and location in the landscape. The goal when watering plants is to make sure water is applied in the root zone of the plant (where it can be used by the plant) and that it is applied deeply – slowly soaking into the soil to at least the depth of the root ball. Shallow watering encourages root growth only at the soil surface, which does not allow for adequate establishment and will not be beneficial in times of water stress. Not sure if a plant needs to be watered? Feel the soil (and not just the soil surface). Keep in mind that rainfall may not be enough or consistent enough for good establishment and that supplemental irrigation may be needed through the first growing season. New plants need at least 1” of water every week for the entire first year.
Pruning. Many times plants are pruned to create a desired shape or to keep a plant a certain size. Plants can also be pruned to rejuvenate the plant and to thin out old, woody stems. Care needs to be taken when pruning plants to consider how plants will respond to the pruning. One common mistake is pruning at the wrong time of year. For flowering plants, when buds are set and when flowering occurs should determine when plants are pruned. The old adage “if it blooms before June, don’t prune” is a good starting point. Many plants that bloom in spring set flower buds the previous year in either summer or fall. If a plant such as forsythia or lilac is pruned in fall or early spring, there is a good likelihood that it will not flower because buds will be removed. Plants that bloom in summer and fall generally set buds in spring of the same year.
Another consideration when pruning is the impact it will have on light exposure throughout the canopy. Plants that are pruned to be wider at the top will result in reduced light penetration to lower parts of the plant. This will reduce plant growth in the lower part of the plant. Plants should be pruned so that they are wider at the base, allowing for better sun exposure.
Renewal pruning can be done to improve the look of older or overgrown shrubs. Over a course of a few years, up to one-third of the oldest, largest stems should be removed to the ground. This will encourage growth of new stems. This will be repeated until there are no longer overgrown stems.
Wrapping evergreens in winter. Use of burlap barriers can help protect evergreens from winter damage. The barrier should be constructed about two feet from the drip line of the plants, especially on the south and west sides or the sides exposed to wind. The top should be left open to allow light and air penetration. Individual plants should not be tightly wrapped as this can trap moisture and increase disease potential. Barriers should be removed in spring as the weather warms.
Amanda Bayer, Extension Assistant Professor of Sustainable Landscape Horticulture, University of Massachusetts Amherst