Powerful Perennials

Joyful childhood memories are always remembered as happening under the friendly shade of the huge trees that encircled our yard. The enormous homemade teeter-totter where we sang made-up nonsense songs as we teetered up and down would never have been as enjoyable sitting out in a full sun spot. The thick rope tire swings and nailed board ladder to reach high to “I dare you spots” in the trees were the best toys imaginable.  Not only are trees where children play but beneath them is where families hang-out for relaxing time or picnics. Trees are valuable! They perform as a protective barrier from the outside world while they provide air conditioning, homes for birds, fresh oxygen in the air and mainly shade in the garden. Whatever is done in a garden, the first priority is to be gentle with trees for they are the basis for all enjoyable outdoor living.

Gardeners often blame tree shade for ruining their flowerbeds. But the culprit may not be the shade but the masses of tree roots beneath the ground that supports the tree. Perennials, heuchera, though it prefers more sun, heucherella and tiarellaare comfortable growing in the shade of trees because of their shallow root systems, but they grow better under trees that do not have shallow roots. In other words; if a shady perennial flower bed is viewed as a problem in your landscape, grow shallow-rooted plants under deep rooted trees. Blaming shade for having a wimpy looking shade garden could be because the soil is jammed full of tree roots that hog all the moisture and minerals, leaving nothing for the plants. All that needs to be done to grow shallow root perennials under trees is to add a layer of mulch or topsoil and get them planted and established before the tree roots have time to move and refill the new mulch.

Shallow-rooted trees

Trees that are undesirable due to shallow root systems are probably members of The Populus tree family for they have found the western mountains their favorite place to grow. This family includes cottonwoods with their shallow aggressive roots, and aspens that sprout new sucker trees as they invade surrounding areas. Another family of shallow root tree is the Weeping Willows or salix. Willows are invasive by the sheer volume of roots they produce. These types of trees expand their root systems into the top layers of garden topsoil and in their relentless search for water are infamous for damaging septic systems. These trees are fast-growing trees for a homeowner who is overly anxious for shade.

It’s said that whoever plants these types of trees is planting only for himself. The deep rooted, slower growing trees are planted for the individual and their grandchildren.

Deep-rooted trees for the Rocky Mountains

(only a few mentioned and all are large shade trees)

There are many deep-rooted, low-zoned trees that are superior in providing shade in a garden so never choose a tree just from a visual glance at the tree or the low price on the sales tag.  Trees are permanent structures that require research and thoughtful choice before purchasing. Here are a few deep-rooted trees for consideration:  Pine Trees are very popular in mountain landscapes and anchor themselves with a strong taproot. Deep rooted trees like Green ash or fraxinus are excellent alternatives to popular maples and oaks for they are extremely cold hardy. Linden trees with their perfect umbrella shaped foliage are dependable and hardy and are adaptable for smaller yards. Before purchasing shade trees for your yard check local extension services to help make the best choices for your area.

A conifer’s root structure consists of a permanent primary root that extends as deep as the height of the tree. A pine tree’s secondary roots sit in the top twelve-inches of soil. Pine trees are like an iceberg with their drip line reaching a distance of two to four times the height of the tree. Losses of perennials planted under pine trees are mainly in winter when they do not get water. Their dense foliage does not allow winter snow to melt through to the ground so any plant in a pine trees drip line suffers from lack of water.

We grow male green mountain ash at our Idaho home. They have been planted along the highway for privacy because of their dense, well-shaped foliage. This is one of four we planted and all are growing beautifully. The male mountain ash is fruitless and fall clean-up is a breeze for the entire tree will turn a brilliant yellow and within a week the leaves have fallen and can be raked.

Picture: chapt. 3, heuchera, ss, fig.5, Tilia, Linden tree

Tilia or Linden with its nice symmetrical foliage looks excellent in both casual and formal landscapes. Lindens have heart-shaped leaves, fragrant spring flower clusters, and turn gold in fall. The straight trunk and high canopy allows sun shine in below the tree but will keep rain water out so a watering system in gardens beneath Lindens is suggested.

These are only samples of the deep-rooted trees that will provide a shady place for relaxation and their roots will not give plants too much competition if the following tips are used. 

• Planting the right plant in the right place is first, as usual, so plant partial or shade plants under trees.
• Partial shade or shade perennials  bloom as readily in a shady garden as well as full sun perennials will bloom in a hot sunny garden.
• Excellent foliage plants are more important in a shady area than flowers.
• Light colored flowers show up better in shade gardens than dark colored plants that seem to melt into the shade.
• Raised flowerbeds for maximum soil and drainage give the best success for growing flowers in shady gardens.
• Many shady gardens rely on the wonderful Alpine ground covers that grow well in shade and stay evergreen like the ajuga shown below.

Perennials to Plant Beneath Shade Trees:

Ajuga or Bugleweed

Ajuga reptans, usually called by its common name of bugleweed is suitable for growing under trees. Caution is advised when planting beneath mature trees to avoid damaging their roots. By adding in a top layer of mulch for planting, ajuga will send out runners to carpet this area into a lovely easy-care garden.

Ajuga reptens is a useful and adaptable ground cover that is attractive year around for it is evergreen to semi evergreen. Ajuga, ‘Bronze Beauty’ and ‘Burgundy Glow’ are the hardiest, zone-three) of the bugleweeds and will fill a western shady flowerbed under trees nicely.

 Ajuga is famous for its vigorous variegated foliage of bluish bronze and rich deep greens. Flowering spikes of deep blue, peak in May and June but will continue blooming into July. Leaving the spikes uncut may result in self-seeding which is an excellent method of germination over tree roots for the seedlings will find their own niche, be stronger and more root tolerant.  Bugleweed’s rhizomes spread by runners, quickly filling in a garden spot with a thick carpet of foliage. In Rocky Mountain gardens ajuga is not as aggressive for our soils are a little more alkaline than it prefers and our winters a little colder but it still performs well but without its usual vigorous tendencies. Ajuga spreads by sending out runners on top of the soil mulch. These runners can be harvested anytime of the year and replanted. Once ajuga grows in a garden new starts will always be available. The runners never compete or damage tree roots. The best time to propagate the runners is when the mother plant is still young. Lift the rooted runners of ajuga and plant them immediately.  Pruning, like fertilizing, is not necessary but if the plants become entangled, simply mow or cut them down to keep the plant contained. A tree’s root system greedily takes all moisture available so even though ajuga is a dry shade perennial occasional watering will keep it healthier.  

Lamium maculatum or Dead Nettle

Lamium is another shallow-rooted, drought-tolerant perennial that does a remarkable job of growing under the challenge of shade trees.  Lamium’s appearance with its silvery foliage adds light and sparkle to a shady area. My personal favorite is ‘Beacon Silver’ that is silver with a green margin.

Lamium, ‘Silver Beacon’s eye-catching nine-inch foliage is silver with a green margin. The long blooming purplish-pink flowers are two lipped with the lips fusing into their throat. It’s interesting that the Greek word for throat is lamios and this explains the name lamium. The peak bloom time for lamium is late April but it will keep blooming sporadically into September.

‘Shell Pink’ is also an excellent ground cover for shade. The leaves of ‘Shell Pink’ are green with a middle silver stripe with pale pink flowers, almost opposite of ‘Silver Beacon’. Both of these fine ground covers will carpet a continuous silver mat of foliage without holes, especially in a raised bed with added mulch or compost. Both are hybrid perennials but show no susceptibility to winter’s cold and are deer resistant. Occasionally deer will eat off the blooms of any spring blooming perennial much to the disappointment of a gardener. Lamium is not fussy about soils and will grow without fertilizers.  Avoid planting lamium in perennial borders for it may spread too vigorously and crowd out the other flowers. Allowing lamium to set-seed usually results in a plant different from the parent and this is usually green with a stripe in the mid-section of the leaf. These reverted seedlings are extremely hardy and will gradually take over the entire shade bed.

Hybrid Lamiums will revert to the original species which is superior in health, spreading abilities and wintering. To keep the silver leafed varieties in a garden, lamium may have to be cut back after its initial big bloom push to prevent seeding and/or the reverted plants weeded out. Many gardeners prefer the original species in their gardens due to it hardiness and spreading abilities.

Ajuga and Lamiums are only a couple of perennials that will perform well in the challenges of a shaded area under trees. Spring flowering bulbs grow naturally well in this environment for they are able to absorb enough sunshine before the trees leaf out. Alchemilla or lady’s mantle with its graceful pleated foliage and bright yellow-lime lacy sprays is delightful under trees and so is convallaria or lily-of-the-valley. Wild Geraniums, especially the big leaf varieties and periwinkle are good choices as well as Hosta which is surprisingly drought tolerant.

The bottom line is being careful not to damage tree roots when digging and planting. Very often a nice shade tree can offer a higher evaluation dollar and more appeal than a newly remodeled kitchen just because of the welcoming feeling they give a home.