UNITED STATES—Environment is what determines what plants grow where. It may sound simple enough, but environment is a combination of many different factors, including but not limited to climate, soil quality and exposure. Each of these factors is a complicated combination of other factors. For example, climate includes temperature, humidity, rainfall, frost dates, winter chill duration, wind and so on.
Home gardening, like the production of horticultural and agricultural commodities, is obviously limited by environment. Plants that want rich soil with good moisture retention are not happy in clay or inert sandy soils. Annual vegetable and flower plants that do not tolerate frost are grown after the last frost, and finish before the first frost. Annual plants that survive frost are grown in between.
Environmental modifications, such as irrigation, fertilizers and other soil amendments, make it possible to grow what would not normally grow in particular environments.
However, environmental modifications are not always practical. For example, if the cost of irrigation of a particular commodity might exceed the projected revenue of that crop, an alternative crop must be grown instead.
pH (the ‘power of hydrogen’) is another one of the many limiting environmental factors. It is what makes the soil acidic or alkaline. Some plants prefer the soil to be slightly acidic with low pH. Some are more tolerant of slight alkalinity with high pH. What we choose to grow in our gardens should be adaptable to the pH of the endemic soil, whether it is acidic, alkaline or close to neutral.
There are all sorts of fertilizers and soil amendments that can modify the pH somewhat if necessary. Such amendments make it possible to grow rhododendrons and azaleas and other plants that prefer slightly acidic soil where the soil is naturally and slightly alkaline. The problem is that the adjustments of pH are not permanent, so it must be maintained. In many situations, major modification of pH is impractical. It is generally more practical to select plants that will be happy with the natural endemic pH.
There are so many more of the fancier cultivars of hydrangea, Hydrangea macrophylla, than there were as recently as the 1990s. Many of the pink and blue hydrangeas were interchangeable years ago. They would bloom blue if the soil was acidic. They would bloom pink if the soil was alkaline. Their color changed accordingly when planted from potting media into soil of another pH.
Most of the modern cultivars nowadays are better at one color or the other. Those that want to be rich pink or almost red might turn lavender or purple in acidic soil. Those that want to be rich blue might do the same in alkaline soil. That makes for many hues of pink, blue, lavender and purple. Most of those that bloom white always bloom white, and their foliage might be a little lighter green.
There is also much more variety in floral form than ever before, although all bloom in summer or autumn with big rounded or nearly spherical trusses of many small flowers. The deciduous leaves are about six inches long, and pleasantly lush and glossy. Modern compact cultivars stay low and dense. Larger cultivars get about six feet high and wide, with somewhat open branch structure.
Horticulturist Tony Tomeo can be contacted at tonytomeo.wordpress.com.