Shade has a very bad reputation with gardeners who blame it for the general lack of success they have gardening in wooded areas. Of course, it’s true that you can’t grow just any plant in shade (vegetables, for example, loath it), but there are in fact lots of plants that will grow perfectly well in shade. I mean plain shade, such as on the north side of a building or under a pergola. Not the shade of trees. Because under trees, the situation is very different.
You see, the real problem of gardening under trees is not so much the shade itself (not if you choose the right plants) as the presence of so many tree roots. These roots dry out the soil, leaving it in perpetual drought, and also deplete most of its minerals while they’re at it. This is called root competition. Some trees (maples, spruces, pines, willows, liquidambars, birches, etc.) are worse than others, with root systems that literally skim the soil surface or even rise above it and really suck all the goodness out of the soil. And make digging hell too! But just about any tree, even the so-called deep-rooted ones, is going to have plenty of roots in the top foot (30 cm) of soil. This combination of conditions – shade and root competition – is what is known as called dry shade.
1. Dig big. You need a big planting hole, as deep as the new plant’s root system and three to four times as wide. The wider the hole, the slower tree roots will be in coming back. So a big hole gives your plant a chance to settle in before the competition arrives.
2. Cut roots as needed. After all, otherwise you won’t be able to dig at all. You’ll need more than a shovel: pruning shears, a hand saw, maybe an axe. Sure, if you hit a big root, move the hole over a bit and start anew, but otherwise feel free to chop the hell out of any secondary roots you run into. Don’t worry that you’ll be harming the tree. A healthy tree can lose a third of its roots in one year and still be in fine shape. It will simply respond to root pruning by growing abundant new ones.
3. Line the hole with 7 to 10 sheets of newspaper. For the same reason as point 1 above: to keep the tree roots from moving in before your plant has settled in. Do not use landscape fabric: you want a temporary barrier that will decompose and disappear over time so your plant’s roots can expand. (And landscape fabric will not keep tree roots out: they’re very tenacious!) Make sure you cut off or fold down any part of the newspaper sticking above the ground; otherwise it will act as a wick and dry the soil out. An added plus is that when newspaper decomposes, it turns into… compost! So it feeds your plant as it disappears, usually within 12 months.
4. Plant only dry shade tolerant plants. Why put in a sun-loving plant like a peony? It will only be miserable. Or a moisture-living plant like an astilbe? It will out and out die. Try hostas, epimediums, Solomon’s seals, bigroot geraniums, hellebores, wild gingers, ajugas, even many ferns. The list of plants that can tolerate dry shade is surprisingly long! Check out my book, Making the Most of Shade for tons of suggestions.
5. Plant only mature plants. This is more important than you think! Young plants, even those that are reputed to be dry shade tolerant, will have a very difficult time settling down in an area that will soon be invaded by tree roots. Even if they do survive, they’ll take forever to reach their full size. But a mature plant, with its large mass of dense roots, will be able to withstand the coming invasion. Plus you get that “well-established garden” look right from the start!
6. Backfill with a mix of good soil and the original soil, then water well. But you already knew that, so skip on to the next point.
7. Give your plantings extra care the first year. That too you probably already know, but I want to insist on it. Any new plant needs extra care at first and plants that will eventually be drought stressed by surrounding tree roots, more than most. You don’t need to keep them soaking in water, but do check weekly and water if needed. The old “finger in the soil down to the second joint” still remains the best moisture meter ever! It it feels moist, don’t water. If it feels dry, do water. And watering is the main care they need at this point. Dry shade plants, practically by definition, don’t need particularly good soil or even much fertilizer, but they do need moisture until they are thoroughly established. Then you can bring on the dry conditions and let them grow on their own.
That’s it! When you apply the right techniques, it becomes a cinch to create a beautiful garden in dry shade.