I’ve come to love using trees as anchoring points for developing new garden areas; a starting point to build from that a messy brain can latch on to and think, ‘Yes! A starting point.’
Planting under established trees is challenging. It’s far easier to buy a young tree, plant it, and plant everything you’d like to see under it on the same day. You should definitely do that instead.
Sadly, few of us have time machines to visit our trees in their youth. And there is something satisfying about making it work, when you are crawling around the raised roots of a maple tree digging into a crevice to plant a tiny fern that you think “will look cute someday.” Maybe you put a rock next to it, to show off the green. It will look cool someday, you tell yourself.
Here are a few moments in the evolution beneath the maple tree in the back yard. Took trying it out for me to realize a pure circle doesn’t work here, at all. On a more traditionally angular yard with fencing and raised garden beds and decks and right angles galore, a defined shape might work okay, but the borders of our yard are swoops and curves. It’s a wild setting, kind of sprawling, and this shape felt like it didn’t belong.
It looks like I slipped a doily under a tree.
Doubling down on a bad idea:
This orientation (below) works better. The plants are still young and I’ll be dividing and continuing to fill the space out this spring, but it feels more satisfying to look at:
Things I’ve learned about planting under mature trees:
Timing: Spring. Early. The cool air helps the soil hold moisture and reduced leaf cover in the trees above. Densely-leaved trees like maples and oaks hover over soil like umbrellas – it takes a good hard rainstorm to soak the soil in those circumstances, and establishing plants need that moisture. A deficit of organic matter helps not at all (more on that below). People always say that planting earlier in the day is best, and it’s certainly better for me because I have less interest in doing anything as the day wears on, but if a plant is going to die because it went into the ground at 2pm instead of 8am let’s assume its chances weren’t great to start with. Water it into the ground with a bottle of water and be done with it.
Soil: Soil under trees is variable, but generally fairly crappy. On the ungenerous soil of West Hatfield, which is a product not of the Connecticut River floodplain but of a bunch of glaciers shoving granite around, soil almost always needs some amending, but plants that will survive in the stingy environment below tree canopies don’t ask for much. I will occasionally use potting soil left in an abandoned pot, or a handful of compost here or there, especially when the planting holes are shallow by necessity. My experience with many natives (which despite much of what I mention here, is mainly what I use around trees) is that they do not appreciate or want the same level of soil nutrients needed to, say, grow tomatoes. Variegated Solomon’s Seal sulked all summer the year I delivered a small layer of composted manure. They are used to fighting tree roots for ‘whatever is left’. Shredded leaf mulch is perfect – nature doing its thing, making soil. I keep shredded fall leaves in chicken wire cages over the winter and use that as needed.
Bark mulch used after planting helps maintain moisture but is not a necessity. If you have it, you have it. It will break down, add to the soil structure, and hold moisture in the meantime. (If tree roots are exposed, they should not be covered.) I lay the mulch between roots, using the roots as Jersey barriers for a little structure, leaving a little doughnut shaped well around the new plant so that water can make it into the soil. Mulch also makes things look a bit more ‘finished’ and deliberate.
Tree roots: And lots of ’em. I will cut small roots here and there if I need to, but generally look to lay plants between the roots.
Water run off: Strategically placed rocks, logs, or even other plants can form a natural container for the new plant and hold soil amendments within that frame. These makeshift berms are helpful on the thin, compacted soil that tends to function like pavement, especially on hillsides, as new transplants send out roots.
Plants: Choose small, scrappy little guys. You want multiple small plants grouped together in order to cover the space over time. If you are able to shop at home, native ferns can be dug up in early spring with a serrated knife and transplanted dormant or nearly-so to their new homes.
Wispy Maidenhair ferns (surprisingly tough) and leathery-leaved Christmas ferns are both particularly good under trees and the foliage contrast works. They tolerate drought and the green leaves complement tree bark. Native geraniums do well too.
Trilliums can be dug up in bloom or shortly after, pre-dormancy (when you can still find them) and brutally hacked at. You will think they won’t survive, and they may give every appearance of immediately dying, but they will likely show up next year. They can be treated like peonies, with their growing points beneath a layer of shallow soil.
Woodland natives work well here: they can tolerate the shade, and they can tolerate the dryness. Since it is mostly or entirely illegal to swipe plants from public land, I shop at home for what is native to our property. I’ve used tiarella (foam flower) successfully, which shouldn’t work but for some reason, does. There is a field of them in a swampy area next to the stream. Surprisingly content in a swamp or in the meager dry shade of a tree.
Hellebores are also easy to move around, particularly if yours seed around widely, as mine do. Small ones can be plucked out of the ground with a spade and moved over. Hostas can be carved out (serrated steak knife) and replanted as soon as they emerge in the spring. Again, you want multiples (you can carve out a piece of hosta as if you were cutting out a pie slice, then tease out growing points in sets of three to replant over several square feet. It will pay off, I promise. Epimediums tolerate dry shade, and are a little magical.
You could also pay for plants, like a normal person. There is some benefit to starting very small, though, and that’s easier to do when you are prying small amounts of plant material from existing mature plantings. You want root systems that don’t ask for more than what the space will provide in the first season. As plants establish, they will become more resilient but you don’t want to have to abandon all other interests to care for the little snowflakes. You also do not want to try digging a hole for a gallon sized Krossa Regal hosta under a maple.
Bulbs: Don’t neglect bulbs: early emerging daffodils, particularly Baby Moon, Tête-à-Tête, and February Gold. If your tree is younger, or has the decency to not be a maple with thick ridges of root system sprawling laterally below the canopy, you may be able to use larger bulbs that need to be a few inches deeper. Ice Follies daffodils are our earliest blooming larger daffodils, and also my favorite, Barrett Browning.
Scilla and crocus work well and are conveniently small, which is nice if you are digging planting holes with your index finger. It helps to hide them among daffodils; squirrels will eat the bulbs but will leave them alone if they have to nose aside ‘Baby Moon’ to get at them. The key is that that after the flowering period is over, the leaves need enough light to photosynthesize to maintain the bulb and increase the colony for next year. If there is a burst of bloom followed by shade, ultimately, the bulbs will not be perennial – they will whither and run out of energy.
