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Durable Plants for Demanding Landscapes

Dr. Dave Creech

The SFA Mast Arboretum, PO Box 13000, Stephen F. Austin State University, Nacogdoches, TX 75962

A paper from the Proceedings of the 10th Metropolitan Tree Improvement Alliance (METRIA) Conference held in St. Louis, MO, September 30 and October 1, 1998, co-sponsored by the Landscape Plant Development Center and the Society of Municipal Arborists.

Abstract

Woody plant evaluation is a long-term process. The introduction of "new and improved" woody ornamentals to the nursery and landscape industry demands many years of evaluation and observation. The researcher waits patiently for record heat and cold, drought and soggy conditions, looks for indications of invasiveness, ease of propagation, and the emergence of significant disease and insect problems. Visual appeal, growth rate and care/culture nuances are recorded along the way and compared to plants already in the trade. All the steps finally arrive at an opinion on the worth and promotion of the particular plant in question. "New" plant introductions are based on the plant's merit in the landscape. Some may fall into the mass market equation with sales in the millions of units while others may fit special niche markets in specific regions. The SFA Mast Arboretum's woody plant evaluation program – "Plants with Promise" – has focused on planting a wide range of species and cultivars in a garden setting and providing good irrigation and weed control in the establishment phase (first two years). No insect or disease control management is employed (except for fire ants) and weed control is handled by Roundup, hoeing, hand-weeding and mulching. The plants described in this paper are uncommon in landscapes, have proven themselves in the Arboretum, and deserve further evaluation in the landscapes of East Texas. They have survived record heat (1998), record cold (1989), and almost every-other-year floods (with 1994, 1995, 1997, and 1998 as major events).

Introduction

The SFA Mast Arboretum is a twenty-four acre garden resource that lies on the main campus of Stephen F. Austin State University in Nacogdoches, Texas (Zone 8a-b). The garden is bisected by LaNana creek, a stream that wanders through the University and the city of Nacogdoches, the oldest town in Texas. Thirteen years after inception on the south side of the Agriculture building, the Arboretum has grown to twenty-four "theme gardens" and is home to over 3000 trees, shrubs, vines, ground covers, grasses and herbaceous perennials. The collection is AutoCAD mapped and a plant accession policy is in place. In 1997, the SFA Mast Arboretum was granted 14 acres across the creek and an eight-acre azalea garden development is underway. Promoted as a community resource, the key features of this new development are an abundance of good soils, irrigation, and excellent public access and visibility. There are two faculty members (Dave Creech and Greg Grant) and one Technician (Dawn Parish) managing a work force of graduate students, undergraduates and volunteers.

Large Trees

Taxodium mucronatum, the Montezuma cypress, is one of the big surprises in the Arboretum. We have found the species to be exceptionally hardy. It easily survived the hard December freeze of 1989 (0°F) and a specimen exists in the Zone 7 Raulston Arboretum at Raleigh, North Carolina (albeit not totally happy). In our region, the Montezuma cypress grows faster than the bald cypress or pond cypress, probably due to needle drop later in the fall and earlier foliage development in the spring. In one planting on the Shelby county courthouse square, the Montezuma cypress is much larger (almost 2X) after ten years than the bald and pond cypress. The species is resilient. For example, in the fall of 1995 and late summer of 1998, the Montezuma cypress lost its leaves in a drought, but quickly reinitiated a new green cloak after rains returned and remains in good health. The species is reported to present less of a problem with knees. We have tested all three at several locations and have always found the Montezuma to outgrow the others. Worthy of planting in Zones 8 and 9 and testing in Zone 7. Taxodium distichum 'pendula' and 'Prairie Sentinel' are superior cultivars of the common bald cypress. Taxodium ascendens, the pond cypress is well adapted, more conical in shape than the bald and easy to separate from the bald (ascending needles on the stem). There are two other members of Taxodiaceae that have performed well in the SFA Arboretum for many years. Glyptostrobus lineatus, the Chinese water cypress, and Metasequoia glyptostroboides, the Dawn Redwood. The former is rare and surprised us by surviving the 1989 freeze with no damage. As a side note, the 25' Dawn redwood in the Arboretum shed nearly all its foliage in mid-July 1998 and has recovered after a long drought with a new cloak of foliage. We have not been able to achieve survival with any Larix species, the true larches; however, we have a few four years-in-the-ground Pseudolarix amabilis plants that look only fair.

Quercus polymorpha, Quercus canbyi, Quercus risophylla and others – The Mexican oaks. This is exciting and uncharted territory but the three listed above have performed well in the SFA Arboretum and in some nearby landscapes. Already in the trade, the trees are easy to establish – they grow quickly in the landscape; the northern limits are not exactly defined but the species have performed well at Zone 7 North Carolina State University Arboretum. My favorite of what we have growing in the Arboretum is Q. risophylla, the loquat leaved oak, a very special tree: leathery, evergreen leaves, columnar habit when young, open and branching with age. Most peculiar, in an attack of cutworms several years back that took all the foliage off the campus and Arboretum red and white oaks, the Mexican oaks were untouched (too much jalapeno sauce?).

Liquidambar styraciflua 'Rotundiloba' is slowly making a name for itself, which it should. With attractive rounded lobed leaves and no fruit, this slower-growing cultivar is worthy of planting. Available as a grafted plant or from micropropagation or tissue culture. We have not seen vivid fall color on our specimens, nor have we observed very much cork development on the limb structure, attributes that give this native a special spot in East Texas landscapes.

Small Trees

Euschapis japonica is one species in the genus and a member of the family Staphyleaceae and a small deciduous tree that appears to be very well adapted to the south. While not yet in the trade, my prediction is that it soon will be. Native to China and Japan, our original plants come to us from North Carolina State University. The species was collected by the National Arboretum in the 1980s. In shade, the species makes an open small-statured tree; in sun, the tree is shorter, dense and attractive. Shoots are stout and attractively striated. Leaves are odd-pinnate to ten inches across and leaflets are ovate-lanceolate to four inches long. Summer flowers lead to the key attribute: an attractive fruit display. Bright red fruits hang from loose panicles, dehisce to reveal jet black seeds and persist for several months (September until leaf fall). The seed appears to have a distinct double dormancy. We have germinated seed after a three-month stratification but the general rule is a 3 month cold-moist regime, followed by a few months at warm-moist regime, which is then followed by another round in the cooler for several months. After that, good stands can be expected. We have not done well with cutting propagation.

Quercus glaucoides, Lacey Oak, is a blue foliaged west Texas oak that has performed well in well-drained sunny locations in East Texas. Reported to reach 20-25 feet tall.

Sophora affinis or Eve's Necklace has been a winner over the years. With light lilac tinted blooms and a striking black seed pod for winter interest, this has been a durable small tree in the Arboretum and in several of our test locations. Native to Arkansas and Texas, the species seems to make the most of any landscape situation as long as the site is well-drained and in full sun. We have found the tree to be exceptionally drought tolerant even during the critical establishment year. Sophora secundiflora, the Texas Mountain Laurel, must be mentioned as one of the sterling landscape candidates in East Texas. It should be planted much more. With a little patience, sun and a sharply drained location, a Texas mountain laurel cannot be beat: evergreen, dense, outrageous blooms and a heavenly scent in the early morning (the kids on our tours cry out, "Grape Kool-Aid!" We have a grey-leafed form and are searching for a hard-to-find white-flowering form, which, for some reason, we do not have in our collection. Lots of opportunity for selection but asexual propagation is difficult.

Acer palmatum and other maples have been easy growers and excellent landscape candidates. Having lost control of our senses many years ago, we are now at over sixty varieties of A. palmatum and do not intend to stop. My only comment is that there is more out there than 'Bloodgood,' 'red,' and 'green'. From diminutive, dense shrub-like specimens like 'Oto hime' to intensely-cut leaf shapes to pendulous to variegated forms, there is something for everyone. We have found the Japanese maple to be dependable, although prone to a little leaf burn in late summer, a condition that depends almost totally on the specific site chosen. We find eastern exposures best and the full force of a western sun should be avoided. Deep shade will allow the tree to grow but color is generally poor. Acer palmatum 'E.P.' a Sherwood Akin introduction is reported to be a good candidate for attempts at growing the species in full sun. We shall see. Acer ginnala, the Amur maple, provides us with a vivid red each spring and our eight year old specimen is over 20 feet and shows no intention of stopping. We have a compact perform is 8' tall in the same amount of time. There are many Acer species that have performed well. Acer buergerianum cultivars coming into the trade show great promise. Acer truncatum has been durable in full sun.

Crataegus brachycantha, the Blueberry Hawthorne, is native to east Texas and Louisiana. It is rarely seen in commercial or residential landscapes. The species makes a very showy small tree with numerous attributes: interesting bark, graceful branch development, a delicate finely-cut leaf, and a bright show of white flowers in the spring. In the Arboretum, unlike many in the Crataegus genus, this species has not been prone to severe rust or other leaf and limb-defacing insects or diseases (note: this species will rust in the nursery, in shade and is prone to disease until well-situated in a full-sun site). The tree has few thorns. To twenty feet in the wild, a specimen is easily managed in a sun to part-shade environment. An excellent small specimen tree, this species is deserving of more use. Crataegus marshallii, the parsley haw, has similar characteristics and appeal.

Daphniphyllum macropodum is a member of the Daphiphyllaceae family, one of 15 species of evergreen shrubs or trees. Native to Japan, China and Korea, this species is adapted to a Zone 7 hardiness zone and performs well in open woodlands. When well-grown, the species is a dense round evergreen mass; oblong leaves are eight inches long and three inches wide, shiny, often sporting red petioles and mid-ribs. Greenish flowers and blue-black seed are somewhat inconspicuous and not key features. D. humile is a related species of slightly smaller stature with similar requirements. Propagation is by seed in the spring or by greenwood cuttings under mist. Seed propagation requires several plants grouped together to insure pollination. Both species are under test in the Arboretum and performing well, albeit growth is much slower than I would like to see.

Pistacia texana, the Texas Pistache, can't quite make up its mind whether it wants to be a tree, or a shrub. The species is dependable in a full-sun, well-drained site. I can also report that Pat McCracken at Taylor's Nursery, Raleigh, NC, has successfully grafted the species on top of Pistachia chinensis. Time will tell what the final growth habit will be – but it's an interesting combination of interest to very few. Hardiness improvement is one possibility.

Styrax japonica cultivars are well adapted to East Texas and rarely available in the state. The Japanese snowbell makes an attractive small tree and features a showy spring bloom. 'Emerald Pagoda' is a large-leafed, large-flowered cultivar, a J.C. Raulston find from an expedition in 1985 to Korea (collected on the island of Sohuksan). Already in the east coast nursery trade, this variety is deserving of much greater use in the south. 'Pink Chimes' is not as pink as we would like - basically much more washed out than when the cultivar is grown further north. 'Carrilon' displays a weeping form (seedlings of 'Carrilon' are often weeping - good potential for selection). 'Isaii' is recently acquired and has not flowered in the arboretum. The Japanese snowbell is a good candidate for a part-shade to full sun environmentand prefers a well-drained, humic soil and even moisture during the establishment years. There are many other species and varieties of the Styraceae family worthy of mention: Halesia diptera var. magniflora (a botanical variety from a community in Florida sporting larger flowers), Sinojackia rehderiana (a floriferous small tree to twenty feet with sytrax-like blooms), Styrax obassia and other species from China look well adapted. Styrax americanum and S. grandifolium, southern U.S. natives, also deserve much greater use.

Cinnamomum chekiangensis, a recently introduced species of Camphor tree, is a promising candidate for east Texas gardeners looking for an attractive broad-leaved evergreen tree. I can't locate the species in any of my references. Our tree was a gift of Kai Mei Parks, Camellia Forest Nursery, Chapel Hill, North Carolina and was collected in China by her husband, Clifford Parks, a botanist at the University of North Carolina at Chapel Hill. The species is evidently quite hardy; only in the gardens three years, the tree has endured temperatures below 11°F. After seeing a thirty-foot specimen at Camellia Forest Nursery, I am convinced we now have a hardy camphor tree for our region. C. japonicum - the common camphor tree grown in semi-tropical and tropical locations, has suffered limb damage from mid-winter freezes during most winters and is no longer with us. The Lauraceae family is large with some 250 evergreen species, mostly strong zone 9 and 10 residents. This rare under-tested species should be hardy into Zone 7. We have observed the tree at SFASU for three years and have found it to be durable and attractive. It was planted as a small specimen in a raised sandy loam bed in the bottomland section of the arboretum. The tree is fifteen feet tall, an attractive dark-green pyramid, and endured a complete blow-down during the flood of October, 1994 (propped back up, some soil thrown, and then staked for a few months). We rooted the species in high percentages with a May cutting collection and have about a hundred one gallons to be distributed. There are two other broad-leaved evergreen trees that may find a place in landscapes: 1) Machilus thunbergi is an evergreen native of Asia, a member of the Magnoliaceae family, and looks promising in the deep South – provided selections are sought that come from cold-hardy stock plants. We have seedlings from a twenty-five year old specimen in Aiken, South Carolina, that has endured below zero freeze events and we have one plant surviving of six clones (National Arboretum) planted just before the 1989 freeze, 2) Phoebe chekiangensis, another rare member of the Lauraceae family, has been a durable conical evergreen tree in our gardens. Like the Cinamomum, I can find little in the literature concerning this plant. All three are interesting broad-leaved, small-statured evergreen trees. (Note: we have two rare Nothophoebe cavalieri plants in our collection soon to be planted).

In the conifer arena there are many strong performers – at least in the early stages of testing. Culivars of Thuja plicata, T. occidentalis and T. orientalis look promising. Juniperus virginiana 'Grey Owl" is a standout specimen in full sun. X Cupressocyparis leylandii and Cupressus species and cultivars appear to be fast growing and attractive when young. The Arboretum's Cupressus lusitanica (?) from seed taken from specimens in Mexico's San Madre Oriental mountain range have made strong growth and features blue-green foliage and a conical growth habit. Cupressus glabra 'Carolina Sapphire' is impressive. Chamaecyparis and Cryptomeria species and cultivars deserve extensive testing. Cryptomeria fortunei has been a standout in a hot, full sun location. Many others do well in a part shade enivronment. The SFA Arboretum is home to 14 cultivars of C. japonica. Chamaecyparis pisifera 'Blue Boulevard' is a striking small specimen tree to ten feet in about that many years and is now available in Texas – good in part shade. Thuja occidentalis 'Filiformis Aurea' is bright yellow with long weeping needles. Thujopsis dolobrata has been a superior plant. In a trial of over forty Juniperus horizontalis cultivars established in 1988 and ended in 1996, 'Blue Chip' and 'Bar Harbor' were superior performers.

Shrubs

Mahonia gracilis, a native of Mexico, has been a stellar performer. Our oldest plant is placed in the worst possible site imaginable: a hard-packed, beat-down east Texas red clay right on the very edge of a hot parking lot in full sun. July is miserable in Nacogdoches. Not only that, the spot was out of reach of the nearest sprinkler head. That meant dry times ahead. We planted a small one-gallon plant there in 1988 as a companion to a strange "shrub oak" from Mexico and then mulched the area heavily with three to four inches of composted pine bark. While the oak has only survived, the Mahonia has slowly matured into a superlative specimen. Fully five feet across and three feet high, this evergreen plant has a lot to offer. New growth is a lustrous lime-green. The winter interest is terrific in full sun, a mixture of oranges, yellows and light green growth. Late-winter flowers are bright yellow and held on slightly erect racemes emerging from held near the terminal buds. Plants grown in part-shade tend to be taller and open. Propagation is difficult; we have failed to root a cutting and seedlings are slow and prone to damping off. We have an excellent seed crop this year and hope to establish plants for distribution. Actually, I think there are many Mahonias that should be planted in Texas for part shade winter and early spring interest. When planted in mass, few plants make a stronger impression. Mahonia fortunei has been dependable. There are several hybrids worthy of seeking out: Mahonia X media cultivars 'Underway', 'Winter Sun", and "Lionel Fortescue." The hybrid betweenMahonia bealei and M. lomariifolia"Arthur Menzies" is a knockout.

Itea virginica – Virginia sweetspire – has long been one of our favorites. Easy to maintain at four feet, the species is a thicket-forming shrub with terrific flower interest in May and good fall color if given enough sun. Sweetspires can handle full sun fine if given mulch and moisture. There are four named varieties: 1) 'Henry's Garnet' is known for a 6-inch infloresence and excellent fall color, 2) 'Longspire' has very long infloresences, 3) 'Sarah Eve' has a smidgeon of pink to the flower, and 4) the latest variety, 'Saturnalia', is more erect and shrub-like (a NCSU release). There are other species of Itea worthy of use: Itea oldhammei and I. illicifolia in the Houston region and Itea chinensis in all regions are good candidates for the part-shade garden.

Vines

We have become vine-crazy at the SFASU Arboretum with a new theme garden that we call the "Lines of Vines." We have planted vines at the base of ten-foot posts and trained them into tree forms for easy maintenance and observation. The place floods about once every year or two - vines go under six feet of water. Standouts include:

Campsis grandiflora - the Chinese trumpet creeper – is a must-plant for any landscaper that can find that full-sun spot. Outlandish flowers to three inches wide, this bright petunia-on-a-stick look will raise the eyebrows of most. Actually, I get more phone calls on this species when it is in bloom than any in the Arboretum. Much less invasive and obnoxious than our native C. radicans, the species roots easily from juvenile wood (going to be an interesting plant for the nurseryman looking for well-timed flowering of product for sale). In the landscape, flowering comes in a surge in late spring and early summer and then off and on the rest of the year, depending on the degree of pruning and training. There are several C. radicans and C. grandiflora X C. radicans clones floating around that offer flower interest and diversity and are worth planting.

Bignonia capreolata 'Atrosanguinea' – the red-flowering cross vine. Our original plant was a gift from the legendary Lynn Lowrey and we have given away hundreds of plants to nurserymen in our effort to see tthat this cultivar gets more attention. Outrageous floral display if the crown of the plant can grow into full sun. B. capreolata 'Tangerine Beauty' is equally floriferous and a fine addition to any Texas garden. Two new ones for us: 'Helen Fredel' and 'Jekyll Island', with the former sporting the largest blooms of any in the collection.

Gelsemium sermpervirens 'Woodlander's pale yellow' – a little diversion from the ordinary traffic-stopping yellow so common in the trade.

Kadsura japonica 'Fukurin' – glossy leaved, evergreen vine with leaves edged to various degrees of cream and yellow - a standout Zone 7 - part shade candidate. Kadsura japonica 'Chirimen' – sports an interesting variegation a cream white marbling throughout the leaf , while Kadsura japonica 'alba' freatures dark green foliage and white-fruit 4)

Lonicera sempervirens 'Leo' – a heavy-blooming coral honeysuckle – ten in our trials with more to be added soon.

Wisteria frutescens 'Dam B' – our native Wisteria – has a much smaller leaf and bloom than the invasive Wisteria sinensis that is commonly seen in the trade. A blue-flowering and white-flowering form is available and the species is easier to control. Wisteria floribunda and Wisteria sinensis cultivars in our line of vines garden are well represented. We like 'Violacea plena' and 'Rosea.' We are looking for our first 36" long infloresence; we're not yet there but are getting closer. Wisteria macrostachya 'Clara Mack' is striking and a prolific bloomer. Milletia japonica is a Wisteria relative with much smaller leaves and less aggressive habit than its more vigorous cousins. Rare in the trade but easy to propagate, we think this species is special.

Celtis sinensis 'Emerald Cascade' – had to fit this one in somewhere – a weeping hackberry that we call a weeping "sugarberry" hoping the name change helps. This geotrophically-challenged brute can be sculpted into almost anything if time and passion are on hand. Easy to root.


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