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How to choose all-star plants: Defining which plants can grow in your garden

by Timber Press on January 9, 2013

in Design, Gardening

Mums are bright, trendy kids who strike a pose in fall, but if kept in the garden, most require plenty of pinching to remind them to be cute. Instead, why not try naturally tidy aster or the spring-spectacular cushion spurge?

The following is excerpted from Andrew Keys’ Why Grow That When You Can Grow This? 255 Extraordinary Alternatives to Everyday Problem Plants

If the garden is the high school musical, then plants must be its cast of characters, and, of course, the cycle of seasons is its plot. Like every good play, then, every good garden must set the stage, and the bits and pieces that make up the garden’s setting tell us what plants will grow best.

HARDINESS

Hardiness is the first growing need to consider in plant problem-solving. The term hardiness refers to how much cold a plant can weather. The U.S. Department of Agriculture’s Hardiness Zone Map is the most widely accepted tool for determining the chill factor of your garden location. The USDA map divides North America into ten hardi­ness zones by average low temperature, then divides them a step further, giving each zone an “a” and a “b” part. That way, gardeners can pinpoint within five degrees the average low temperature where they live. When you’re on the hunt for plant problem-solvers, make note of a plant’s hardiness rating on its tag. If, for example, it says “Zones 5–10,” you’ll know that, in trials, that plant survived low temps from hardiness zone 5a (−15 to −20 degrees F/−26 to −29 degrees C) to 10b (35 to 40 degrees F/4 to 2 degrees C).

It’s also important to know that even if a plant is “zone hardy,” all zones are not created equal. Heat and humid­ity are supporting players in the garden setting. After all, Zone 6 in cool Massachusetts, a location where relative humidity and precipitation are high, is a far cry from Zone 6 in the high, dry desert of New Mexico. Right now, there’s no tool as accepted as the USDA Zone Map for determin­ing a plant’s penchant for heat, but we’ll talk about heat and humidity in the big picture and what they might be like where you live in a moment. A basic awareness of cli­mate will go a long way toward helping you pick the right problem-solver in terms of heat, cold, and hardiness zone.

LIGHT

If you’re choosing a plant for a certain spot, keep an eye on that spot for the next few days. Does it get full sun (five to six hours or more of sunlight per day), part shade to part sun (three to four hours), or full shade (one or two hours or less)? Lots of plants also grow great in light shade, which means filtered or reflected sunlight for much of the day—light that shines through the branches of tall trees, for example.

Now take a look at the light requirements for the plant you wish you could grow. If it’s a sun-worshipper and you garden in a shady location, or vice versa, it’s probably time to search for a problem-solving plant. All plants get their energy through photosynthesis, a process for which sun­light is required. Some plants need more of it, and some thrive on less. Sun is also a hot-button issue—literally. With sun comes heat, and while some plants may like it sunny, they may not like it hot. Because the sun’s rays tend to be more kind in the morning, some all-star plants do better with a little shade in the heat of the day.

As a Mediterranean native, Italian cypress gets the sniffles in cold, damp northern climes.’Shawnee Brave’ and ‘Degroot’s Spire’ make great, and hardier, alternatives.

WATER AND SOIL

Water and soil are two plant growing needs that are inex­tricably linked, like star-crossed lovers. Plants need water especially during the growing season, when they’re actively packing on roots and shoots. How much average rainfall does your garden get when plants are at their growing peak? Would that plant you wanted to grow wilt if you couldn’t water it enough? You’ll need to water even the most drought-tolerant plants for a time when they’re newly planted to get them settled in, but if an established plant continues to wilt dramatically without lots of water, odds are there’s a low-water all-star that would be happier with the amount of water that falls naturally from the sky where you live.

Water and soil both play roles in drainage. If you find it’s mucky not too far below the surface of your garden’s soil, or if water pools for days or weeks in your garden when it rains, you definitely have wet soil, also known as soil that doesn’t drain well. Wet soils occur near bod­ies of water or places where water pools—rivers, ponds, lakes, and streams.

While boggy conditions can be a challenge for some plants, many plants actually prefer moist soil, a step down in dampness from wet. Since water helps with the break­down of organic matter—what gardeners know as that good stuff that comes from great compost, for example, or decaying leaves or bark mulch—nutrients tend to be more readily available for uptake by a plant’s roots.

Dry soil can be more challenging. If you garden in a location where water doesn’t reach or collect readily in the topsoil—a sunny hillside or under a dense canopy of mature trees, for example—you may deal with soil that dries out more quickly. Most plants do fine in average soil, a compromise between wet and dry, and the major­ity of plants at nurseries will have tags that tell you they prefer soil that’s well-drained. Translation: they like water, but they’d rather not sit in it or go months without it.

But wait—there’s more to soil and drainage than meets the eye. Soil’s role as a complex character also lies in its makeup. Is your soil clay? Is it sand? Is it more like loam, with plenty of organic matter? You’ll find all-star solutions that do well in each soil type, and each has its own quirks.

Clay soil, for example, gets mucky and doesn’t drain well when it rains. It also hardens to a plant-killing crust dur­ing drought. But guess what? Clay is high in the nutrients that plants love. It may need to be worked a bit to unlock those nutrients and improve how it drains.

In contrast, sand wants nothing to do with water or nutrients— water runs right through it. Sandy and rocky soils often are lean, drain fast, and leave plants holding the bag. The good news is that plenty of plants love these lean soils, too.

Loamy soil is the type in which most gardens grow most readily. The secret to loam’s success lies in its diversity of particles—some tiny, like clay, and some big, like sand—as well as plenty of organic matter, breaking down and pro­viding good stuff for the ecosystems of tiny life that exist in all soils, as well as plants.

Soil pH, a measure of soil acidity or alkalinity, can be a big deal too, as it influences a plant’s ability to absorb nutrients. Some plants, like those that have adapted to live under the canopies of conifers, would much rather grow in acidic soil. Others, particularly many desert plants, prefer alkaline soil. Soil pH is measured on a scale from 0 to 14, with 7 being neutral. A rule of thumb is that soils higher in organic matter that’s breaking down tend to be more acidic, while soils that are low in organic matter are more alkaline.

Confused yet? Don’t worry! There are a few easy ways to unearth your soil’s potential. First, read up on the typical soil in your part of the country. Next, get a soil test—a real one, not a DIY kit from a store. Odds are a nearby college or university has a lab that does soil testing. It’s as simple as sending them a bag­gie with a form, and voila! They’ll reply with a wealth of information on your soil and what grows there, including its composition in terms of sand, loam, clay, organic matter, and other things, as well as pH. They’ll also tell you whether it’s worth attempting to amend your soil—that is, adding various components like organic matter to help plants grow better.

MAINTENANCE

What is maintenance? Maintenance is pruning, water­ing, mulching, amending the soil, raking leaves, and mowing the lawn. It’s is everything you have to do to keep your garden going. It takes time, and a lot of people resent it, including me.

Maintenance is so important for many garden plants because they’ve been bred to live solely in your gardens. Plants can’t prune or mow or spray themselves for bugs, so these tasks fall to you. In the world of garden plants, maintenance can be as key to survival as any other growing need, but while the other factors we’ve discussed come part and parcel with a garden’s location, mainte­nance is down to you. It’s your garden—how much work will you put into it?

Maintenance is a touchy topic in this busy day and age, as well it should be. Many a popular problem plant whose mug shot is a poster child for high maintenance. Most plants need at least a small bit of care at some time in their lives, and while many problem-solvers may be low maintenance, the zero-maintenance garden is a myth.

GEOGRAPHY

Different regions set the stage for the garden play in different ways. Here’s a breakdown of those regions, moving clockwise around the continent.

The Northeast and Midwest stretch roughly from the Great Lakes to the East Coast, and feature cold winters and summers that are hot and humid, but relatively mild compared to neighboring regions. All-star plants should enjoy moisture year-round—below-freezing winters with frozen ground and snow that segues to rain in spring. Summers aren’t as soggy, but they come with thunderstorms. Areas along coastlines are cooler and drier in summer because of wind, and milder in winter. Everything gets more extreme away from the coasts, with hotter summers and colder winters. Since these cold-weather regions are also home to lots of deciduous trees that lose their leaves, the soil tends to be high in organic matter and more acidic.

The same goes for soil pH in the Southeast, much of which has the added bonus of an abundance of red clay. If there’s one thing a southern gardener knows, it’s that climate here tends to be humid year-round. Winters are mild and wet, and temps may dip below freezing, but not so much that the ground freezes. Summers are the pres­sure cooker of seasons, with extreme heat coupled with high humidity. Thunderstorms bring periodic relief. All-star plants have to take the heat and wet, as well as soils that may not drain so readily.

Following along, we come to the Southwest, where climate transitions from humid to arid, and as tree cover becomes less common, soil transitions from acidic to alkaline. Winters are mild but chilly, and this is when the region gets most of its rainfall. Summers are hot, hot, hot, with high humidity in eastern portions of Texas—where it’s more likely to rain some in summer—that tapers off into the dry heat of the true deserts of New Mexico, Arizona, and southwestern California. All-star plants must be able to withstand drought and thrive in soils that are lower in nutrients.

The West Coast trends from dry to wet. Coastal regions of California see Mediterranean climates, with cool, mild winters when rainfall is plenty, and dry summers with low humidity and little to no rain. Summer temps range from mild to hot, with more extreme heat inland. All-star plants here need to handle prolonged periods of drought. Up the coast in the Pacific Northwest, drought becomes less of a concern as the climate turns to mari­time. Summer temps become mild, and there’s rainfall aplenty year-round. Warm ocean currents make winters wet, but usually mild as well.

The Mountains region includes the area from the mountains of the West Coast to the Rockies, and just on the other side. Between the mountain ranges, winters are cold and wet and summers dry, with areas of high desert and low humidity. Here, all-star plants have to deal with extremes of temperature and lack of moisture. Soil can be lean, and higher elevations bring dry air—just as valleys are a bit more temperate, because moister air pools in lower-lying places.

Finally, the Great Plains are a return to more extreme seasons as you move from west to east—perhaps the most extreme in terms of shift. East of the Rockies, in the vast plains at the center of North America, humidity returns, and with it summers can be a steam bath. Winters can be similarly damp, with excesses of snow, but they can be dry as well, especially in the southern plains. Though all-stars here must deal with these extremes, the plains are blessed with some of the continent’s richest soils, and plants benefit from that.

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Andrew Keys is a writer, designer, consultant, and lifelong gardener. The host and producer of Fine Gardening‘s Garden Confidential podcast, his writing has appeared in Fine Gardening and other magazines, as well as on his blog, Garden Smackdown.

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“It’s nice to have this as a source book for choosing plants for my garden when I’m tired of pandering to something I already have or I’m ready for a change. Andrew’s book can be a help towards gardening smarter, not harder!” —Kylee Baumle, Horticulture

“The key to Keys is the way he nudges us out of our box, and gets us thinking. … This is ‘teach a man to fish’ stuff that will hold its value, no matter which new plant alternatives come along.” —Toronto Gardens blog

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