Monday, March 21, 2016

The Right Plant for the Right Place by Rebecca Anderson

Photo courtesy
When Master Gardeners and Extension horticulture staff are helping people with plant problems, we usually start with the soil.  It is thought that 80% of plant problems are related to soil issues.  We like to start with soil testing to find out if there are any deficiencies or excesses in the soil that can be corrected so plants will grow better.  But what happens when the soil test doesn't show problems and your plants still aren't thriving?  What else could be going on?

Photo Courtesy Rebecca Anderson, native plant garden newly planted

Photo courtesy Rebecca Anderson, native plant garden five years later
It's a good idea to take a wider look at the plant's location.  What is the sun exposure where the plant is growing?  Most flowering plants need 6 to 8 hours of full sun every day. Others are shade loving like impatiens. There's a mantra in the horticulture world: "Right plant, right place."  It is very difficult to make a tender plant thrive in a hot, exposed location, just as it is tough to have a sun-loving plant exist under a shade tree. This sort of evaluation of plant placement needs to be repeated periodically. For example, a maple tree may not have been making much shade over nearby rose bushes 10 years ago when it was planted, but today it may be causing problems. 

Another fact to to consider is the other plants growing near the struggling plant. There are certain plants such as black walnut trees that release allopathic chemicals that prevent other plants from growing too close. This is a protective mechanism for the walnut tree to keep it from getting crowded, but it doesn't help the other plants that were placed too closely.  As plants grow over time, ones that may not have been crowded initially may become too close together. This can lead to competition for resources such as nutrients and water. The possibility of disease also increases because airflow between crowded plants is diminished and it is easier for pests to move from plant to plant when the plants are too close together. 

Watering techniques should be evaluated as well. Too much water can be just as harmful as too little.  Plant roots need access to air in the soil as well as water and nutrients, and excessive water fills in the air spaces between soil particles, essentially drowning the plants. Automatic watering systems are increasing popular, but they still need to be monitored over time. Plants' needs change as they grow and they also change with weather patterns. Don't forget to turn down the irrigation when it rains and consider increasing watering a little when it is hot and dry.  Not all plants have the same water requirement, so it helps streamline irrigation by placing high water use plants in a separate area from more xeric individuals.

Soil can still be a source of problems, even if the soil test numbers show nutrients are adequate.  One big problem along the Colorado Front Range is compaction.  In many areas the soil is predominantly clay and it compacts easily during the home construction process.  Compaction restricts the movement of air and water through the soil, starving plant roots of needed nutrients.  The soil here also tends to be alkaline (has a high pH), which not all plants are adapted to.  Plants that thrive in acidic soil, such a blueberries, will struggle in the native soil of this area. 

A little bit of planning can go a long way when adding new plants or replacing struggling ones in the landscape.  Don’t forget to check the plant’s needs against the conditions of the site.  Consider the mature size of the plant compared to its neighbors and try to allow enough room for everyone.  A landscape is a living, growing and evolving space so don’t be afraid to make changes as seasons pass.  A weak or overgrown plant may not be a problem but an opportunity to try something new!

For more information on finding the right plant for the right place, see Colorado State University’s CMG Garden Notes #512 .