Frustrated Homeowners and Challenging Conditions

Planting around tree roots, especially when they’re giant and growing above the ground, is one of the most common questions frustrated homeowners ask me. Gardeners often end up feeling defeated and either 1) don’t plant anything, or 2) end up planting a lawn around the tree, which has its own set of problems like damaging the roots or trunk with the mower. It’s a challenging situation to be sure, but there are certainly many plants that will thrive in this environment.

I have some tips and techniques to share that will help you overcome the obstacles. But first, let’s talk about why planting under trees is more of a complex issue than people realize. Generally speaking, tree roots grow above ground because they’re growing in a less-than-ideal space. Or perhaps there’s been soil erosion. Or it might be a variety that tends to grow that way. There are lots of reasons.

An extreme example is shown in this photo where the giant tree is crammed in between a street and sidewalk, leaving very little soil for the poor tree. The roots are starved and are desperately seeking oxygen and nutrients above ground. But most of my clients don’t have tree roots that are this exposed – usually there are only a few large roots above ground with a solid mat of roots just under the soil’s surface. Needless to say, they’re frustrated because the plants they’ve tried just don’t thrive.

Challenging Conditions for Plants

Plants usually don’t do well when planted close to a tree’s trunk or within its drip line because a tree’s roots are the first to take any water and nutrients, leaving very little behind for any remaining plants. Yes, the big dog eats first. Not to mention, it’s a nightmare to plant anything larger than a 4″ pot thanks again to the surrounding tree roots, so larger plants (1-gallon and up) are squeezed into whatever hole could be dug with minimal amendments added.

Some gardeners build a circle around the tree, adding 8 or so inches of new soil and consider this spot a brand-new raised bed. Sound like a tempting and simple idea? Don’t do it. Most trees have shallow feeder roots just under the soil’s surface, and when covered with more than a few inches of soil, they can quickly suffocate. The disastrous result can be an untimely death of the tree.

Planting Strategies for Tree Roots

So how do you plant around a tree’s roots? In this photo, a lush mat of creeping phlox was planted via small plugs. And that’s the key right there – plugs, groundcovers, and 4″ pots. I never use 1-gallon sizes under trees for the reasons above, not to mention I don’t want to permanently damage the roots by digging that much either.

And speaking of damaging roots, it’s critical to use caution when planting under trees to minimize the destruction of the feeder roots. Sure, even when planting small plugs or 4″ pots, you’ll undoubtedly end up cutting through some of these roots, but fear not – the damage will most likely be minimal. As a general rule, don’t cut any root thicker than a Sharpie pen.

I’ve grouped my favorite plants for under trees into 3 main categories: Bulbs, Groundcovers, and Perennials (including grasses and succulents). Generally speaking, when it comes to plant selection, I stick to those that not only have shallow root systems but are also drought-tolerant and shade-tolerant.

Bulbs for Under Trees

Spring bulbs can be a great choice to plant under deciduous trees – even those that need full sun to bloom, like daffodils and crocus. While the tree is deciduous without winter leaves, bulbs appreciate the sun. Yet once the tree’s spring leaves appear, most bulbs are finished blooming and won’t be affected by the shade. Plus, the small size of bulbs means they’re easier on you and the tree to physically plant around those imposing roots.

Some examples of bulbs that grow really well among a tree’s giant roots include cyclamen and late winter bloomers like the ones featured in my recent article Planting Around Tree Roots. Cyclamen bulbs easily re-seed among a tree’s roots, adding much-needed late winter color.

Groundcovers for Under Trees

Groundcovers are ideal for planting around large tree roots as they’re often available either as flats, 6-packs, or 4″ pots. There are tons of options available, but the following are just some that have shallow roots, require little water, and do well in partial shade.

Geranium cantabrigiense ‘Biokovo’ is hands-down my go-to groundcover for shady, low-water areas. This variety is evergreen in my zone-9 garden, with a heavy show of pale pink flowers in the spring and summer. But even when not in bloom, it remains a tidy and well-behaved 2-4″ tall, slowly spreading mound, whereas many other varieties get leggy after time. Its roots are also incredibly shallow, allowing it to easily re-root in those difficult patches near exposed tree roots.

Ajuga is one of my favorite groundcovers to plant in difficult sites such as around tree roots. With a little added water, it quickly spreads into a dense mat. Yes, it can be invasive, but with a little yearly thinning, you can easily keep it in check. My favorite variety is ‘Primrose Heron,’ which spreads less and has unusual yellow-green spring foliage. Both Ajuga varieties do well in part shade.

Epimediums (Barrenworts) are excellent groundcovers, slowly spreading in dry, shady sites. They have the sweetest little flowers too. Satureja douglasii (Yerba Buena) is another amazing little groundcover with shallow roots, low-water needs once established, and quickly spreading to 2′ x 6′ wide. It smells like mint, and I use it throughout my garden in any shady spot where I want a lush patch of evergreen. And when given afternoon shade, it’s happy as can be.

Rubus pentabulus (Creeping Raspberry) is another deer-resistant, low-growing groundcover perfect for under trees. It needs a little summer water to do well and has slightly prickly stems that re-root along the ground to 4-feet or more.

Larger Plants for Under Trees

I’ve included Grevillea ‘Fanfare’ in the groundcover section because, even though it’s typically available in 1-gallon sizes, it’s still fantastic for planting under trees. The reason is simple – because it spreads to 10-feet or more, it can be planted farther away from the tree’s drip line and allowed to spread. I’ve found it also does really well with part-shade with no reduction in flowers. Oh, and did I mention the deer never touch it, it’s super low-water, and the hummingbirds go crazy for it?

Similar to the Grevillea, Ceanothus is another example of planting a 1-gallon plant farther from the tree trunk and letting it spread to fill the space under the tree. There are several low-growing varieties such as ‘Centennial’ or ‘Carmel Creeper,’ and all are loved by pollinators and hummingbirds.

Perennials, Grasses, and Succulents

Many of the perennials, grasses, and succulents I recommend are available in flats, plugs, 4″ pots, or are easily planted from small cuttings or transplanted seedlings. If you’re having problems finding them in 4″ pots, try asking your local nursery if they can request some from their grower. I’ve had great luck with this.

Heuchera maxima is another go-to perennial to plant among tree roots. It’s often available in 4″ pots and is easy to start from small cuttings. It’s much larger than other Heuchera varieties, growing to 18″ x 18″ with tall wands of white flowers lasting for weeks. If you have a bit more water to offer, Tiarellas are also perfect for tree roots for the same reasons – they’re a bit smaller (12″ x 12″), but many have striking foliage with cute little spires of flowers.

Centranthus (Jupiters Beard) is usually found in 1-gallon containers, which means you should plant it outside the tree’s drip line. However, when happy, the Centranthus will gladly re-seed itself around the tree, meaning you get the flowers without digging and damaging the tree roots. Both the white-flowered variety and the more common red-flowered one are low-water and tough as nails.

Bergenias are another super tough, low-water perennial that are typically only available in 1-gallon sizes. However, because they quickly multiply and transplant so easily from cuttings, they’re ideal for tucking here and there among tree roots. And even when not in bloom, the oversized evergreen foliage is beautiful on its own.

Succulents and Ferns

I have oak trees throughout my garden, which, as you may know, are very sensitive to having their roots disturbed. Succulents are fantastic for planting among the tree roots as they have shallow roots, are very low-water, and appreciate partial shade. If you’d like to read more about the other plants that live in the dry shade under oaks, click here.

Many ferns do wonderfully well planted under trees thanks to their shallow roots. Alas, it’s too hot and dry in my climate to plant most varieties. There are a few exceptions that do well in my hot and dry garden, which are the Western Sword fern (Polystichum munitum) and the Japanese Holly fern (Crytomium falcatum ‘Rochfordianum’).

Grasses for Under Trees

Grasses are fantastic to plant around tree roots as they’re often available in 4″ pots or may re-seed, allowing you to transplant them. Deschampsia cespitosa (Tufted Hairgrass) requires a bit more water than my garden has to offer, but the following grasses are much more drought-tolerant:

I hope you’ve enjoyed this post and that it’s given you some hope in what to plant in this very challenging situation. I thought I’d share with you what inspired me to write this post in the first place.

A few weeks ago, my friend gave me this vintage Sunset magazine from almost 75 years ago. It’s amazing how the gardening-related articles seem as though they could’ve been written yesterday – in fact, except for all the ads and recommendations to buy every pesticide under the sun to blast the life out of all those pesky insects (thank heavens we’ve moved beyond that!). Even the title of the article, “The Right Flower in the Right Place,” is as popular now as ever. But if you look at the first section covered, it talks about what to grow under trees – hence my inspiration.

I love seeing your daily videos – it makes me think I’m there in your garden with you! Wishing you and Tom all the best as you continue to forge forward in your beautiful garden.