Gary Zimmer, Curator of Gilman Park Arboretum in Pierce
Every once in a while we horticulturists face an event that “puts us in our place” and reminds us how little control we have over the landscape. These events aren’t necessarily all bad, and can be used as a learning experience. For me, these events usually involve my incessant “pushing” of the border between hardiness zones 4 and 5. I’ve had many successes with zone 5 plants—and also quite a few failures. But last summer we dealt with a totally different challenge that I’m hoping will become a valuable learning experience.
After the Flood Receded
June 2010, following several days of torrential rains, about a third of the 10+ acres comprising Gilman Park Arboretum was under 1-5 feet of water for six days. Of course, even after the flood waters receded, the soils remained saturated for several weeks. Since this portion of the arboretum is in a designated flood storage area, I have known all along this was a possibility and had taken that into consideration when selecting plants for the area. It has flooded many times over the years, but never more than two days at a time; and I found out neither I nor the plants were prepared for flooding of this magnitude.
My first inclination, viewing the area after the waters receded, was to just cry. The area looked “totaled.” Fortunately I had learned from other natural events to simply leave it alone for awhile. The worst thing to do is to give up or start ripping things out.
Documenting the Affects
Almost immediately I saw that this could be a great learning experience; that I could document what happened to help myself—and others—in future planning and planting. So even though I didn’t really have the time for it, I made the time and started documenting what was happening. As a result, I now feel comfortable making recommendations for others in similar circumstances. Some of these observations may even be valuable for homeowners selecting landscape plants for heavily or over-irrigated turfgrass lawns. If a tree or shrub could survive this flood, they should be able to handle just about any amount of irrigation they receive.
One of the unknowns from this experience is whether older plants would have fared better. Many of the trees and shrubs that were killed were relatively young, small plants; older, more established, plants may have survived. Still, for what it’s worth, there are three broad generalizations I would make about landscape plants for flood-prone areas:
- Don’t plant viburnums. I don’t like saying that because I love viburnums, but they just don’t seem to be able to handle extreme wet situations. Few of our viburnums survived and some that did are still, more than a year later, recovering from severe damage. However, there was one very dramatic exception to this warning and for me this was the most amazing revelation from the flood. Despite all the destruction in our viburnum collection, a pair of Viburnum dentatum ‘Blue Muffin’ shrubs, with 4 of their 5 feet of growth submerged in floodwater, never lost one leaf. I was, and still am, simply amazed. That’s one tough plant! Another exception is Viburnum sieboldii ‘Wavecrest’. This 3-foot plant looked totally dead but, within a couple weeks, it came back with a vengeance from basal shoots and looks better today than it did before the flood.
- Do plant dogwoods. On a few of them, lower limbs needed to be removed, but virtually all the dogwoods survived.
- No surprise here, but don’t plant evergreens. Any evergreen. The only evergreen that survived the summer, Abies nordmanniana, was totally dead this spring. And Picea mariana supposedly tolerates flooding, but all five of our 6-9’ black spruce were killed outright.
A Record of the Damage
As I mentioned earlier, I kept detailed records of everything that happened in the ensuing days, weeks and months. The damage was put into nine different categories, ranging from “killed outright” to “no damage at all.” Some plants looked good immediately after the waters receded, but died within two months. Some lived the rest of the year, but were dead this spring. Many lost everything below the waterline, but remained healthy above. Some had total dieback, but later began recovery from basal shoots. Still others lost most of their foliage, but put out new buds on existing wood. It was truly amazing to watch the differences in reaction to the flood.
There were many surprises for me—both positive and negative. Some notable “good” surprises were the lack of damage on things like ‘Blue Muffin’ viburnum mentioned earlier, wisteria, Cercidiphyllum, redbud, magnolia and witchhazel. Negative surprises involved the many maples and larches that died, which I thought would handle flooding better. And of course there were trees that are supposed to be hardy and proved to be so—oaks, birches, hickories, buckeyes and baldcypress—all of which I would recommend for flood-prone areas and even heavily irrigated lawns.
I also documented damage to perennials, and again there was a wide range of response. Two perennial gardens were totally under water for six days. I was resigned to them being total losses but there were surprises here too. The “Wet Mesic Garden” was specifically designed to handle flooding, and there were some disappointments. Lobelia, Eupatorium ‘Prairie Jewel’, Chelone and Ligularia were all killed when others survived with little or no damage.
The perennial bed at the arboretum entrance was almost entirely wiped out though surprisingly all the ornamental grasses survived: Molinia, Miscanthus, sedges and even little bluestem. I was able to “make lemonade from lemons” with this garden, though, and hopefully this can be an inspiration for others in similar situations. The area had turned into one big weed patch and I was hesitant to replant anything since flooding may recur, but then I looked closer and it hit me… I don’t have to plant anything! Amid all the weeds were scores of little quaking aspen trees expanding from the colony at the back of the garden. It was a poor site for a perennial garden anyway and the aspen colony is an arboretum favorite for many people. What a golden opportunity to let the colony expand right up to the entrance structure! I did some cleanup and I’m anxious to see what it will look like five years from now. Gilman Park Arboretum will never be quite the same again, and in some ways that’s alright. Maybe, with the lessons learned, it will be even better someday.
2010 FLOOD DAMAGE – GILMAN PARK ARBORETUM
Several days of heavy rain in mid-June resulted in flooding of approx. 1/3 of arboretum. Water was from 1-5’ deep over the affected area for 6 days. After water receded, soil was very wet for several weeks.
WOODY PLANTS | KILLED OUTRIGHT:
- 2 Buxus var. koreana x B. sempervirens ‘Glenco’ 1’
- Sassafras albidum 1” cal.
- Carpinus 1” cal.
- Acer pseudosieboldianum 1” cal.
- Betula lenta 1 ½” cal.
- Acer triflorum 4’
- Larix sibirica 2’
- Viburnum burkwoodii 5’
- Betula uber 8" (very young, small trees)
- Corylopsis spicata 3’
- 2 Nyssa sylvatica 3’ (larger one survived)
- 5 Picea mariana 6-9’
- Ulmus thomasii 1 ½” cal.
- 2 Acer pseudoplatanus 4’ & 5’
- Viburnum burejaeticum 5’
- 2 Viburnum x bodnantense ‘Dawn’ 4’
- Viburnum trilobum ‘Redwing’ 1’
- Halesia carolina 3’
- Pseudotsuga menziesii ‘Glauca’ 2’
- 2 Hydrangea macrophylla ‘Endless Summer’ 2 years old
DIED LATER – WITHIN TWO MONTHS
- Picea pungens 12’
- Pinus parviflora ; 2” cal. 6’
- Larix kaempferi 3” cal. 12’
- Acer truncatum ssp. mono 3 ½” cal. 10’
- Abies homolepis 2” cal. 6’
LITTLE INITIAL DAMAGE BUT DEAD IN SPRING
- Acer triflorum 3” cal.
- Abies nordmanniana 4” cal.
TOTAL DIEBACK WITH NEW GROWTH FROM BASE LATER
- Aesculus x mutabilis ‘Induta’ 2’
- Viburnum sieboldii ‘Wavecrest’ 3’ (very vigorous new growth)
- Aesculus x arnoldiana ‘Autumn Splendor’ 2 ½” cal., 8’
TOTAL DEFOLIATION OF ENTIRE PLANT WITH NEW BUDS & LEAVES ON OLD WOOD
- Staphylea trifolia 4’
- Buxus microphylla ‘Wintergreen’ 3’ (very limited)
- Buxus microphylla var. koreana 4’ (very limited)
- Viburnum nudum ‘Winterthur’ 3’
- Lindera benzoin 5’
- Viburnum sargentii 3’
TOTAL KILL BELOW WATERLINE – BRANCHES REMOVED
- Quercus dentata 2” cal.
- 2 Magnolia stellata 10’
- Carpinus caroliniana 7” cal.
- Cornus kousa chinensis 9’
- Heptacodium micronoides 8’
- Cornus mas 12’
DEFOLIATED BELOW WATERLINE WITH NEW BUDS & LEAVES LATER
- Quercus mongolica 10’
BRANCHES KILLED BELOW WATERLINE – NEW SHOOTS FROM BASE
- Viburnum lantana 10’
- 2 Hamamelis vernalis 6’
NO DAMAGE AT ALL – EVEN TO FOLIAGE UNDERWATER From my observations, I would not hesitate to recommend any of these plants for use in wet or flooded areas or in heavily irrigated turf areas. This list does not include larger trees (over 10 yrs.) that had no damage.
- Wisteria macrostachya ‘Aunt Dee’ 9’
- Campsis radicans 2 ¼” cal.
- Cornus sericea ‘Isanti’ 5’
- 10 Taxodium distichum All sizes
- Nyssa sylvatica (smaller ones died)
- Asimina triloba 3’
- Cornus sericea ssp. stolonifera ‘Flaviramea’ 7’
- Salix exigua 7’
- Cornus sericea ‘Kelsey’ 2’
- Cornus racemosa 15’
- Viburnum carlesii ‘Cayuga’ 5’
- Viburnum sieboldii ‘Seneca’ 6’
- Viburnum dentatum ‘Blue Muffin’ 6’
- Betula papyrifera ‘Prairie Dream’ 5’
- 3 Cercidiphyllum japonicum 3 ½” cal.
- Quercus ellipsoidalis 2 ¼” cal.
- Carya ovata ; 4” cal.
- Quercus nutallii 1 ½” cal.
- Quercus michauxii 1” cal.
- Betula potannini 4” cal.
- Ulmus Americana ‘Valley Forge’ 4” cal.
- 2 Betula fruticosa 2” cal.
- Populus tremuloides Many, all sizes
- Carya tomentosa 2” cal.
- Cornus drummondii 2 ½” cal.
- Cephalanthus occidentalis ‘Sputnik’ 6’
- Sambucus Canadensis ‘Lancinata’ colony
- Viburnum opulus 6’
- Quercus acutissima 2” cal.
- 2 Cercis canadensis 1 ½” Cal.
- 2 Cercis canadensis ‘Northland Strain’ 3” cal.
- 3 Aesculus glabra 3” cal.
- Aesculus parviflora 5’
PERENNIALS | KILLED OUTRIGHT
- Monarda ‘Marshall’s Delight’
- Solidago rugosa ‘Fireworks’ (few came back in spring)
- Ligularia dentatum (few came back in spring)
- Aster umbrellatus
- Heuchera micrantha ‘Palace Purple’
- Eupatorium altissimum ‘Prairie Jewel’
- Liatris pycnostachya ‘Eureka’
- Lobelia cardinalis
- Lobelia siphilitica ‘Blue Select’
- Chelone lyonii
TOTAL TOP-KILL WITH GOOD RECOVERY FROM ROOTS LATER
- Rudbeckia fulgida ‘Goldsturm’
- Physostegia virginiana ‘Vivid’
- Cacalia suaveolens
- Heuchera richardsonii
- Lilium superbum
LITTLE, IF ANY DAMAGE
- Eupatorium purpureum
- Miscanthus sinensis ‘Strictus’
- Carex muskingumensis
- Filipendula rubra ‘Venusta’
- Schizachyrium scoparium ‘Blaze’
- Molinia caerulea ‘Skyracer’
- Iris pumila
- Geranium sanguineum ‘Johnson’s Blue’
- Helenium autumnale ‘Rotgold’
- Asclepias incarnata
- Iris pseudacorus
- Iris versicolor
- Lysimachia punctate ‘Alexander’
- Spartina pectinata