The science of the gardens

By Lynette L. Walther | Nov 03, 2017
Photo by: Lynette L. Walther The type of roots a perennial possesses will determine how and if it can be divided. These dahlia tubers are produced as the plants grow over the summer months. Each of these tubers will produce a new plant.

My college physics class was not exactly one of my favorites, but I clearly recall one moment in that class when I sat up and took notice. That ah-ha moment paved the way for the rest of that class to help me understand the world around me. That split-second of insight struck when the instructor described how, after the clouds clear and the sun comes out following a ripsnorting thunderstorm, everything appears greener. You know that effect.

Turns out that greenness isn’t just an optical illusion, but is a physics-class turning point! The electrical energy in lightning separates the nitrogen atoms in the air. Those atoms then fall to earth, diluted within the rain water and combine with minerals in the soil to form nitrates — which those of us who garden recognize as fertilizer! It’s elementary: Lightning + rain = fertilizer.

John Fromer knows how science and the garden are no strange bedfellows. In fact, Fromer, who with his wife, Kathy, runs Appleton Ridge Flower and Vegetable Farm, recently spoke to a lunchtime seminar at Merryspring Nature Center on that very topic and shared some garden science facts.

He discussed the classifications of plants — annuals, biennials, perennials and beyond that, herbaceous perennials (those that die back to the ground in the winter) and woody perennials (those that do not). Former spoke about leaf shapes and stems and roots, too. Annuals live one season -- plants such as snapdragons, green beans, calendulas and tomatoes. They grow, bloom, fruit and set seed and die in one growing season.

Biennials produce foliage only their first growing season, plants such as foxgloves, parsley, mullein or some hollyhocks for example. Their second growing season, they bloom, set fruit and produce seeds and die. Perennials live more than one season, though not all perennials are long-lived. Some only live a couple of years. Examples are agastache, Maltese cross or delphinium. Herbaceous perennial examples are daylilies, Kirengishoma or liglularias. Woody perennials include many shrubs, tree peonies, rose of Sharon and climbing hydrangea.

All of those plants differ in many ways, including their root systems. Roots are one way to determine which perennials can be divided and which cannot. For instance, those with a tap root — plants like lupines, baptisia, sweet Cicily, monkshood and the like are difficult (but not impossible) to divide. (Experts suggest slicing the taproot along its length to divide, something I have not tried.) Taproots are known for their ability to pull nutrients from seep down, making plants like comfrey good additions to compost piles because of the extra nutrients their leaves and stems contain.

“Root hairs only live one to two days,” Fromer said. Those “hairs’ or tiny roots increase the area that roots can absorb water and nutrients. This is one reason vigorous weeding around perennials and annuals during dry times can disturb, even damage those tiny hairs on plants. Same goes for the stems and leaves of adjacent plants, because they are the “circulatory” systems of plants, distributing the sugars that plants create through photosynthesis and the water and nutrients absorbed through the roots.

Another factor in the science of growing things is the pH, or acidity, of the soil in which plants are grown. Some plants, like hollies and hydrangeas, for instance, benefit from a slightly acid soil and fertilizers for those plants are often labeled as being for “acid-loving” plants. However, not all plants like acid. If the pH of the soil in which some plants are grown is too acid, they will not be able to extract the proper nutrients from the soil because the nitrogen is bound up. Applying the correct amount of lime can correct this balance, and that is why Fromer recommends soil testing to be certain how much lime to add and when. Or if soil needs more acid, for certain plants.

“Lime takes about six months to activate the soil,” Fromer said. “Put out lime in the fall for it to be available in the spring.” My weedy mix of a “lawn” which is composed of a variety of grasses, clover and an occasional weed, stays green even when the summer temps go up and the rain fails, in part because of appropriate applications of lime — no other chemicals required. Unlike monoculture lawns of nothing but grass, my lawn is a haven for pollinators. The presence of buttercups in my eclectic lawn tells me that my soil has an excess of acid, so lime is applied.

Fromer also noted that shade plants often benefit from additions of potassium, while full-sun perennials would not necessarily need more. But a soil test can tell anyone for sure what is needed. A lawn, a garden of vegetables or ornamentals, is not much different from those science experiments we conducted back in the day. Only difference is that now we get zucchini, or tomatoes or delphiniums instead of a passing (hopefully) grade. You could say, it is science in action.

Plants with tap roots, like this perennial baptisia, are difficult to divide and transplant. Understanding which plants can be divided and how to do it is all part of the science of growing things. (Photo by: Lynette L. Walther)
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