This summer’s brutal heat and drought have been hard on the landscape, with dead trees and damaged lawns everywhere. We returned from traveling in late June to find our garden slowly turning to toast. The hostas were brown, crispy potato chips, and the swamp-loving box elder was the first tree to die. Japanese maples and yew hedges became blondes under the searing summer sun. Some trees would look fine on Monday and be completely brown before the weekend. In most cases, the oak, pine, maple and ash trees already had some hidden damage that weakened them and reduced their resilience. Dogwoods, red buds and sassafras all started dropping their leaves. One day in July, the thick carpet of fallen leaves under my sycamore made me think it was October.
If you have an irrigation system in your garden, your losses might have been minimal. Others tried to save their plantings by dragging hoses across their lawns in the vicious heat. Decisions were made about which things to save and the wise gardeners opted to save the trees and the shrubs, letting the lawn go. Smart move. Trees reflect generations of care, add value to the landscape and are expensive to remove. They also contribute to energy conservation, storm-water control and environmental quality of life.
All this newly vacant space gives us a great opportunity to rethink our planting schemes and replace the lost materials in our gardens. As we commonly say in horticulture, the loss of a specimen tree, shrub or perennial gives us 'a new planting opportunity.' So, make the best of a bad situation and plant for the future. I shall be reducing the lawn size to the barest minimum to accommodate my two German shepherds. Converting lawn to a shade garden saves mowing and conserves water by thick mulching. Trees cool the air and their shadows help keep our homes comfortable and make parking lots bearable. There are many reasons to set aside our old-school notion that lawns are necessary.
The punishing heat and drought we suffered this summer pushed many plants in our normal landscape palette over the edge. We witnessed one of the highest summer mortality of trees that I have ever seen, and it taught us valuable lessons for the future. We need to assess our planting choices and irrigation options to assure the continuing beauty of our Missouri gardens and city streets.
New Twists and Old Favorites
J. Frank Schmidt & Son Co., a wholesale tree grower in Oregon, has some great new varieties of ornamental trees for urban settings. The new releases for 2012-2013 begin with our stunning, scarlet photo beauty, ‘Afterburner’ tupelo (Nyssa sylvatica, black gum). This new selection offers a straight central leader, high gloss summer foliage and burning red fall color.
Straight to the Sky Columnar Trees
For very narrow places, like the planting strip between the sidewalk and the street or the driveway and the lot line, try a fastigiated-form tree. These grow very narrowly and reach straight up instead of sideways. Schmidt offers the new ‘Armstrong Gold’ maple (Acer rubrum group) with brighter leaf color and density, golden-orange fall foliage and a very neat upright, columnar growth form (40 feet tall by 12 feet wide at maturity).
The ‘Emerald Pointe’ hardy rubber tree (Eucommia ulmoides) has a similar shape (40 feet by 15 feet) and offers very deep green, corrugated leaves that turn yellow in the autumn.
The ‘Skinny Genes’ oak is a second-generation selection from the ‘Crimson Spire’ series (Quercus robur x alba, red oak crossed with white oak) and offers extremely narrow columns (45 feet by 10 feet). If you want to make a living wall, this oak would make a great choice with rich, dark, mildew-resistant, glossy green leaves that turn yellow in the fall.
Rounding up the columnar group for 2013 is the ‘Lindsey’s Skyward’ bald cypress (25 feet by 10 feet). It is a deciduous conifer with medium green fine foliage that turns a rich rusty russet just before leaf drop.
Heat Resistant Selections
The ‘Highland Park’ maple is a cross between big-tooth and sugar maples. It grows fast and is more upright that its parents, but has that traditional glorious autumn coloration. With thicker, tatter-resistant leaves, it should fare better in the occasional hail storm and offers more heat resistance than species sugar maples.
The ‘Summerburst’ golden rain tree (Koelreuteria paniculata) is a wonderful rounded-crown mid-size tree, reaching about 30 feet by 30 feet over time. On a quick look, one might notice the richer lustrous green foliage that turns yellow in the fall or the pink seed capsules that hang around after the panicles of yellow flowers fade. What you might not see is the improved symmetry of the mature plant or the increased heat resistance until the tree has been around for a while. This is a good tree to incorporate into the border because it will give some shade for heat relief and protection of perennials, without smothering them out. You can also use it poolside, where it offers lasting summer bloom to seed pod interest.
The ‘Emerald Avenue’ hornbeam, released in 2011, offers superior heat tolerance and yellow fall foliage on a single-trunked selection of our native Carpinus. ‘Native Flame’ is a more informal selection with improved red fall color.
The ‘Crimson Sunset’ maple gives summer color with deep purple leaves that hold up to the heat. It adds depth to the fall palette with bronzy-maroon richness.
Noble Trees - Stately Kings of the Landscape
The juried list of recommended shade trees for our neighboring community of Kansas City starts off strongly with four oaks in the top 10 for large landscape trees. They rated white oak (Q. alba) and swamp white oak (Q. bicolor) No. 1 and No. 2 respectively. The White oak is one of my lifelong favorites for its beauty, durability and usefulness. It is the source wood for oak-split baskets, acorns for wildlife and barrels for aging bourbon and single malt Scotch. Bur oak (Q. macrocarpa) and chinquapin oak (Q. muehlenbergii) round out the list at No. 9 and No. 10. All four are Missouri natives and top the list for longevity.
Other long-lasting giant treasures are feathery textured ‘Green Whisper’ bald cypress, Michael Dirr’s gingko selections include ‘Presidential Gold’ seedless and ‘Golden Colonnade’ columnar forms,‘Espresso’ Kentucky coffee tree, ‘Raven’ dawn redwood and the hybrid London plane. Also making the list for longevity are the new sunset maple hybrids and disease-resistant American elm selections. Superlative native tree species include black walnut and northern catalpa.
Some of Henry Shaw’s trees still happy after 150 years in the Missouri Botanical Garden include two ginkgos near the Climatron, bald cypresses near the parking area and the osage orange grove at the Children’s Garden. Hundreds more of his selections can be seen nearby in Tower Grove Park.
The Ugly Ones
There are many trees that should be avoided in our planting plans – ones that break during storms, root into our sewers, attract undesirable wildlife or shed trashy plant parts. Some choices are simple. Don’t plant a mulberry over the driveway unless you want to wash your car every day in fruiting season. A gumball tree (Liquidambar styraciflua) over the patio can cause similar distress, but can be worth the fall color if you can place it in the back bed where the spiky fruits fall harmlessly into mulch. Some of the horror trees to avoid include:
• Invasive tree species such as Bradford pear, Amur maple, chinaberry, tree of heaven, mimosa, white mulberry, sawtooth oak, white poplar, Siberian elm and Norway maple.
• Messy trees like cottonwood, fruit trees and sweetgum.
• Brittle trees that shatter in storms such as Bradford pear and silver maple
• All of the ash trees, including both green and white ash, that will be destroyed soon by Emerald Ash Borers.
A Sorry Sight – Death of Dogwoods
One of the hardest-hit species in our native woodlands was the beautiful white dogwood. These succumbed to the drought by the thousands. With broad leaves that lose moisture quickly, the dogwoods were toast by the end of July. Many of them will never recover and will be missed for their fairyland spring bloom. Dying alongside the dogwoods were the native red-buds. Both species are shallow rooted and require frequent rains. These will be lost on the hillsides or perhaps survive in the wetter low slopes and bottoms. I have struggled with suggestions for plants to replace them. As far as the redbuds and dogwoods go, I think placement will need to be given more consideration in the future. As homeowners, we’ve pushed them out of the shadows, so to speak, and in to the full sun. We need to start planting them as they occur in nature—in shade or clinging to edge of the tree line for afternoon shade.
The crape myrtles are similar in size and scale, but their summer bloom doesn’t fill the spring niche. The Amelanchier laevis ‘Spring Flurry’ or A. grandiflora ‘Princess Diana’ fit the spring bloom spot, but I cannot vouch for their drought tolerance. The hawthorns may be a little tougher, with the white ‘Lavalle’ and ‘Snowbird’ hybrids, rosy reds of ‘Crimson Cloud’ and ‘Paul’s Scarlet’ and the Washington species (Crataegus phaenopyrum) normally perform well here. I have seen both Japanese tree lilac (Syringa reticulata ‘Ivory Silk’), Chinese tree lilac (S. pekinensis ‘China Snow’) and seven-son flower (Heptacodium miconiodes) growing in the heat of southern China without irrigation, so they might be suitable choices for small summer flowering trees.
The hardest part of all of this is to realize that we will face brutal summers like this more often in the future. If we want our gardens to keep looking great, we will need to re-evaluate our planting choices. Think about heat and drought tolerance. Look south for ideas, give up the large lawns and plant more tall shade trees along the streets and around homes. These steps will make a huge difference on the how our landscapes look in the future. Plan well today and plant wisely for tomorrow.