Surviving Zone Denial: Establishing Exotics in Your Backyard

By James E Powell

For some, greenhouses are an attractive, albeit expensive alternative to battling hostile interior winter climates. But heating costs coupled with the ever-present threat of power outages or running out of the appropriate fossil fuel amount to a different battle in the same war. What we really want are palms and other tropicals in our yard (well, what we really want is a milder climate, but we can't all live in Florida).

I experienced this frustration firsthand when I became a homeowner several years ago. My first home was located in zone 6b. The house was new, and it had neither a large nor established yard. Grass was sparse, competing with reddish patches of mud for sunlight. The sunlight turned the grass a crisp brown and the mud into crusty reddish concrete. The few pitiful trees and shrubs that passed for landscaping in this yard suffered enormously under the sun. So much so, that over a couple of months I laid to rest a pair of dogwoods and two crippled lopsided maples. They made better mulch than shade.

So I had a chance to start fresh. Since I like variety, I promptly decided I would grow one of everything. That's the advantage of loving plants, unlike Noah, you don't have to find a mate for each new acquisition. Most of my choices we of the hardy, evergreen variety. Despite the fact that I'm allergic to pines and all other shapes and forms of conifers, I like having green around all year. So like a painter, I dabbed the yard with all manner of juniper, spruce, cedar and pine, both large and small. But the results were more like modern art, than a Monet. But it was my first yard to do with as I pleased, and so I did.

Soon, I started eyeing plants at the edge of my zone, and plants that normally grew farther south or in more temperate zones on other continents entirely. This wasn't the first time I'd drifted into what some refer to as "zone denial." Years ago, I lived in first floor apartment with a front garden. There, I discovered that callas come back every year with just the slightest protection from the elements. I also found that blue passionflower vines are root hardy here, and that sago palms are not. Much to the dismay of the rental office, I also discovered that wisteria roots have a fondness for cracked sewage lines.

It was inevitable then that plants with uncertain ability to tolerate our long cold winters would creep into my new yard. My first experiment was with a simple red camellia. For some reason, I decided it would look best planted at the front of the house, facing west. This is one of the most exposed locations in the yard. The winds are bitterly cold and incessant in winter here. The plant tends to disappear under snowdrifts, concealed beneath thick coatings of ice every winter. Yet, this camellia is always flowering by February. Success!

Next, I tried blue Atlas cedars. Everything I read said they were only hardy to Zone 7. We're definitely in Zone 6. Sometimes, I wonder if we are really a Zone 5. I looked up blue Atlas cedar in six or seven different gardening guides before I found one that contradicted all the others and claimed it would survive in Zone 6. That's what I wanted to hear. I promptly bought and planted two.

This past winter we had over three weeks of weather where the temperature barely reached the upper teens each day. There was snow cover for over a month. What was for many (elsewhere in the country) the warmest winter on record, managed to freeze my pond almost to its bottom and somehow kill several koi that had lived in it for over three years. Whether they froze or suffocated, I never knew. I stood on the pond one cold morning pouring warm water laced with food coloring onto the surface in an attempt to thaw through the thick layer of ice. But by then it must have been too late. The koi didn't make it, but two blue Atlas cedars survived with no visible damage.

I decided to try another exotic conifer: the monkey-puzzle tree, which is found in mountainous regions of South America. I bought the largest specimen I could find, a potted plant that stood about 8 inches tall. Monkey-puzzle trees in profile are easily as alien and exotic to look at as flattened, wind-swept acacia trees on the plains of Africa. They have short, broad, deep green leaflets covering practically every inch of the plant. Hollywood has a fondness for showing dinosaurs wandering along the edge of monkey-puzzle forests, no doubt looking for something more suitable to eat. Each leaflet bears an extremely sharp pointed tip, so planting, pruning, or even walking near one can be a painful experience. Unfortunately, my first plant died. It died before winter set in, so I knew it wasn't cold weather, and I suspected it had been partially separated from its roots in shipping or when I planted it. So I tried again.

Sure enough, the monkey-puzzle is perfectly at home here, despite the harsh winters. I have two small plants in my yard that have survived the winter without a single leaf turning brown. They experience several growth spurts during the spring, summer, and fall but aren't fast growers. Still, they there is no point in a monkey-puzzle's life cycle at which they are uninteresting, if not downright peculiar. Their dark spiny whorls are completely impervious to the cold. They have become my favorite non-cycad gymnosperm.

At this point I became bolder, and tried three more exotic plants. I planted a small eucalyptus, a hardy banana from Japan, and a hardy palm native to North Carolina. The palm turned out to be a sturdy, slow-growing evergreen. Numerous snows blanketed all but the tips of the fronds, yet when I bothered to brush the snow back once or twice out of concern, I found that the palm was unharmed. The eucalyptus grew rapidly the first year, then suffered because of my excessive attention (see below) during a harsh winter. Yet its roots managed to survive, and the entire shrub survived a second winter, even managing to grow in chilly February, during a warm spell. The banana was a gamble. I read it was hardy to Zone 7 (like the blue Atlas cedar). It grew into a five foot shrub its first summer, then turned to a gelatinous pile after a few frosts. I made a mound of the remains over where I thought the roots might be, and come May, it was putting up its first leaves.

Then the ultimate test: establishing a hardy palm. I decided to try two varieties, both from neighboring North Carolina. Sabal minor is a trunkless fan palm with large pale green fronds. It and related species grow all over the southeastern United States. I bought a large plant from a mail order nursery and planted it up against the house, on an eastern exposure. Then, I ordered another variety that I had not heard of before. The needle palm, Rhaphidophyllum hystrix, is another fan palm from North Carolina that is often referred to as the hardiest palm in the world. The plant is considered fully hardy in zone 6. It has darker almost grass-like fronds and grows very slowly. I planted this plant in a more exposed location near a fence. By mid-January, the Sabal palm was brown to the soil line, but just beneath, it was obviously still alive. On the other hand, the needle palm seemed impervious to the cold. It survived bitterly cold nights, and it also survived covered with snow and ice for several days without any ill effects. While it took the Sabal palm months to produce new growth the next year, the other hardier palm even managed to grow a little during the occasional warm spells in February and March. It seems hardier than some of the plants I could buy at local nurseries. Success at last!

Getting started outside your Zone

Are palms, exotic conifers and other ornamentals out of the question for your outside garden? Definitely not! Gardeners are beginning to discover a number of hardier than expected exotics that can take the worst a Zone 6 winter has to offer. Plants such as the needle palm and the exotic monkey puzzle tree brave the wind and snow just as readily as the somewhat less exotic blue Atlas cedar from North Africa. Other plants manage very well with just a little protection, such as extra mulch or a nearby wall. A combination of strategies can give your yard a unique and tropical appearance without the hassles of moving potted plants in and out to achieve the same effect.

A selection of hardy exotics:

Needle Palm (Rhaphidophyllum hystrix -- native of North Carolina)
What northern gardener wouldn't get excited at the prospect of growing a palm in their yard? Well, the needle palm is perhaps the world's hardiest palm. The plant is reported to survive temperatures well below zero degrees Fahrenheit with no damage, and this is something that I can attest to myself. With only one summer to establish itself, my needle palm, growing near a fence but well away from any heat radiating surfaces, survived snow, sleet, ice storms, and late cold snaps that sent other hardy tropicals into a subterranean retreat. When the chill passed, the fronds appeared slightly mottled but the plant stayed green and even managed to grow a bit during warm spells from late autumn to early spring. The plant has a very classic palm appearance, so your friends won't have to use their imagination to figure out that yes, that really is a green palm frond poking out of the snow in your yard.

Culture details:
This trunkless fan palm is extremely hardy, but slow growing. Mulch around the base helps preserve moisture, which speeds the plants' growth. In Zone 6, an established plant can survive winters with numerous nights in the teens, and occasional cold snaps that drop to zero. No cover is necessary but placement near a wall or fence is desirable to encourage early spring growth.

Saw Palmetto (Sabal minor - native of South Carolina)
If one palm just isn't enough, here's another somewhat less hardy palm for everyone in Zone 6 or below. The large deep green fan-shaped fronds emerge from the ground in late spring and well into fall. But unless the plant is wrapped and protected, these leaves will turn to straw-colored ghosts by January. Still, don't despair, because unless the ground freezes, this palm will return in the spring to once again grace your garden with its tropical presence.

Culture details: Another essentially trunkless and moderately hardy fan palm is Sabal minor. If wrapped in burlap and planted near a building, this plant can maintain its leaves year round. Otherwise, all exposed fronds die back to the ground. It benefits from heavy mulch and lots of water. It is a slow grower and will tend to fade away after a few years of heavy winters without protection.

Eucalyptus (Ecalyptus neglecta - native of Australia)
Even if you don't have a pet koala bear, you will want to give this fragrant beauty a try in your temperate garden. This eucalyptus can grow into a large shrub if the winters aren't too severe. It maintains its round bluish-silver leaves as an adult, unlike some other eucalyptus varieties. It grows best during the warmer months of spring and summer, but will continue to grow into December if the weather stays warm. I made the mistake of covering my plant with a cardboard box during an exceptionally cold week in February, and forgot to remove it as the days grew warmer. What I found when I removed the box was a desiccated shrub that did not grow despite my best efforts. But in late May, a new shoot appeared at the base of the plant.

Culture details: This bluish green eucalyptus retains its attractive round leaves into adulthood. Although sometimes advertised as cold hardy below zero, this plant tends to die back to the ground if it experiences a prolonged cold snap in late spring. Heavy mulch can protect the lower stem and provide studier and faster growth in the spring. I also discovered this past winter that this plant does not like to dry out in winter. So be sure to water it about once every two weeks if it is dry and cold.

Monkey-Puzzle Tree (Auracaria araucana - native of South America)
Monkey-puzzle is a name used to refer to several species of Auracaria, a tropical conifer family that includes the Norfolk Island pine. There's nothing puzzling about the plant, a monkey simply could not climb its barbed branches! This native of the mountains of Chile has reportedly been grown as far north as British Columbia. It endures snowfalls in its native habitat, and seems to do quite well during cold Zone 6 winters. This tree resembles nothing you've ever seen growing in Zone 6 before, but is no more cuddly than a cactus or a porcupine, so it pays to plant it in an out of the way section of your garden where it can be enjoyed�from a distance.

Culture details: This prickly conifer features a trunk and branches covered in broad, short dark green leaves. Once it starts growing in the spring, it tends to continue to grow all summer, with new growth emerging as soft, light green tufts at all branch tips. This plant likes to stay on the moist side when young. It can tolerate cold wet winters and snow with no visible damage. It benefits from being placed near a wall or fence, and from mulch around the base, mainly to avoid drying out. Another somewhat less hardy species in this genus (Auracaria bidwillii) has more of a Norfolk Island pine look with long narrow leaves covering the branches. But this plant needs a good deal of protection or it will die back to its roots in Zone 6. After a couple of cold winters, it will die. Covering young plants with a mound of mulch in winter will allow them to become established, and a burlap wrap during the coldest months is essential.

China Fir (Cunninghamia lanceolata)
The china fir is remarkably similar in appearance to A. bidwillii, but is much hardier. It has slightly longer leaflets that curl down a bit at the tips. It is also less prickly than the Auracaria. The leaves turn an attractive bronze in winter, then revert to a vivid green in the spring. The underside of the leaves is almost white. It is a fast growing tree that branches often. It can ultimately reach 30 feet.

Culture details: It doesn't appear to require any special protection from the elements in Zone 6. Mulching helps to keep the plant from drying out during long, cold, dry winters. Rich, well-drained soil will produce rapid growth from spring through mid summer.

Calla (Zantedeschia sp. - native of South Africa)
Callas have been getting more interesting in the last 20 years. Once upon a time, there were three basic colors: pink, white and yellow. Today there are variants ranging from green to almost black. After the plants bloom, they continue to put on a show with their compact, upright, sometimes variegated foliage. In Zone 6, callas return year after year with almost as much reliability as hostas and other more traditional fare. Like many aroids, they experience a dormancy period in their native South Africa, so a Zone 6 winter is simply a variation on a theme for them. As long as the bulbs don't freeze in the ground, they will return and gradually spread to form large masses of tropical leaves and exotic blossoms year after year.

Culture details: Yes, the common calla is easy to winter over outdoors in Zone 6. Mulch is essential, and a location close to a sidewalk, wall or fence will help avoid damage during exceptionally cold winters where the first inch or so of the ground freezes briefly. Since they experience a dry cool period in nature where they die back to the roots, Zone 6 winters are compatible, if more severe with their natural cycles. Pile 4-6" of additional mulch over the bulbs in late fall for added protection and larger plants the next spring.

Black bamboo (Phyllostachys nigra - native of Japan)
Tropical and temperate regions throughout Asia are filled with great many varieties of bamboos of varying shapes, sizes and colors. Until recently, I was sure that I could grow any bamboo as long as it was green and dull. But the black bamboo has proven to survive Zone 6 winters. It grows more slowly than its hardier cousins, and tends to dislike cold drying winds, but with just a little protection and a little extra water in the winter, it can form dense stands filled with beautiful purplish-black canes and deep green leaves that can add a tropical air to a dull, unattractive garden corner. Some varieties are actually grown for timber in Japan.

Culture details: Black bamboo is less hardy than some of its cousins but the deep purple canes are well worth the effort. Good mulch and constant moisture is essential and this plant suffers in an exposed windy location. For good results, it must be planted against a wall or fence, which provides protection from the prevailing winter winds. If you must try it in a windy location, wrap the canes with burlap in late November and leave them wrapped until early March. It may take a couple of years to become fully established.

Cordyline australis ("False Dracaena 'spike'")
A houseplant has escaped into the temperate garden! When I first heard that this dracaena-like plant would return from its roots in the spring, I was highly suspicious. When I planted mine in an out of the way but not at all protected spot in my garden, I wrote it off in the fall. But late December, it was still growing and green, despite numerous frosts and cold nights. Finally, a hard freeze in January caused the plant to topple over and die. I was sure it was gone then. But in May, not one, not two, but three new growth tips appeared around the fibrous stump of the previous year. And even though I didn't think it would have time to make much of a show, the three new plants have all produced dozens of thin green sword-shaped leaves this year.

Culture details: This plant is increasingly common at garden centers of home improvement shops because of its exotic growth habit and appeal as both a houseplant and as a point of interest in a bed of annuals. It turns out that it is also modestly hardy and will return from the roots in late May, if mulched sufficiently. Oddly enough, it tends to stay green and even continues to grow until the coldest days in January, when it abruptly topples over and dies. One plant often produces multiple growth points in subsequent years.

Blue Yucca (Yucca rostrata)
Few if any yuccas save the ground hugging thorn tipped varieties seem to grow in cool Zone 6 climes. But this silvery blue upright variety can withstand the harsh winters of colder areas, and will eventually grow into a small trunked shrub 6-8 feet tall. Its ability to survive colder weather is due in part to its thick generous root structure, and to its narrow thin leaves. It is a strikingly beautiful plant that happily endures hot dry summers as well. Plus it is more approachable that its hardier though duller cousins.

Culture details: This beautiful blue yucca forms a ten-foot trunk over time and its leaf color is as blue as the Atlas cedar. It will grow in any sunny location, once established. It requires no special protection in Zone 6. Its thick roots penetrate deep into the soil so there's little chance an especially cold winter would kill off this desert beauty.

Tree cholla (Opuntia imbricata)
Many species of Opuntia will grow in colder climates, but only a couple of varieties of prickly pear cactus are commonly cultivated. However, some chollas will also survive Zone 6 (and even Zone 5) winters. The tree cholla is a many-branched upright grower that bears little resemblance to its cousins. The glossy green cylindrical stems are covered in spines, and turn purplish in winter.

Culture details: Like all cacti, it prefers sandy, well-drained soil. It requires no special protection in Zone 6. If your area is subject to frequent rains in spring or summer, you may need to use some type of stones to reduce problems with erosion. Maypop Passionflower (Passiflora incarnata)
What plant is as tenacious as poison ivy, as vigorous as crab grass, as fragrant as honeysuckle, and as blue as the sky on a fall day? Well, a maypop, what else? This plant can climb 20 feet or more, bear dozens of exotic blue flowers, and form numerous pithy but sweet lime sized fruits all in a single summer. Its only flaw is that it spreads rapidly underground, so the following year you might find it tumbling over your other perennials and winding its way up nearby trees. Still, it is easy to control since the stems remain narrow and pliant, and if all else fails, you can let the first few frosts take care of the problem for you.

Culture details: One of the hardiest members of the passionflower family, this vigorous vine dies back to the ground in late fall, but returns in multiples in late spring. It tends to spread rapidly, so be prepared to accommodate or cut back the additional shoots. The beautiful fragrant blue flowers appear from July until frost, and a tasty, if pithy greenish fruit the size and shape of a small lime is occasionally produced along the vine.

Musa bajoo - native of Japan
Okay, so you've made it this far and said, yes I can see this or that plant might survive one of my long cold winters, but a banana? No way! Well, think again. This banana has all the classic features of its cousins, which fill the produce shelves with over (or under) ripe fruit throughout the year. But it doesn't provide edible fruits, just tropical comfort. While it does promptly turn to mush after the first hard frost, the roots happily bide their time underground until the ground warms sufficiently in the spring. Then, multiple trunks emerge rapidly forming a small tree 4-8 feet tall in a single summer. In a sunnier location, the midrib of the leaves will turn red.

Culture details: With their thick fleshy stalks and broad green leaves, a banana is the epitome of the tropics. But this hardy banana from Japan can be grown in chillier climates with sufficient mulch. It dies back to the ground at the first sign of frost, but returns in mid spring from the roots. It should be planted near a wall and in a less windy location to avoid tattered leaves and additional stress. A thick layer of mulch is a requirement. It also likes plenty of water. Regular waterings result in more vigorous growth in the summer, and a greater likelihood of survival in a severe winter. The plant is sort of self-mulching. You can leave the dead trunk and leaves where they fall as extra protection during the winter.

Various Amorphophallus species
While some may look like small, flat-topped trees, the summer growth of these exotic plants from Southeast Asia is actually a single leaf. The first sign that something is a bit odd about this plant is the trunk - it is fleshy and pale, with numerous dark spots. But if your blooms in early spring, then you already knew this plant was not your average ivy, so to speak. The flower looks like a large black calla, but smells like a large dead animal. Like callas, it endures a dormancy period (before the monsoon season), so as long as the tuber doesn't freeze, it is happy to wait for spring. Eventually, you may end up with a dwarf forest as it spreads in all directions forming little tubers that may not make their presence known until the following year. Just keep the windows shut during its flowering season.

Culture details: The voodoo lily is a very peculiar addition to any garden. The large tubers will survive cold winters with some mulching, and the plant experiences a dormancy period in nature (albeit one due to lack of rain rather than cold) so a rest does not harm it. In the spring, large tubers produce a single blackish-purple flower atop a spotted stem. The flower looks and smells somewhat like rotten meat, since the plant's pollinators in the jungle are flies. The flower fades after 1-2 weeks to be replaced with a single leaf that looks like a canopy of leaflets.

Carnivorous plants (Sarracenia and Drosera species - southeastern United States) Water gardeners who've had their fill of water lilies are starting to discover marginal plants. In nature, more amphibious cousins that grow at the waters edge accompany water lilies and other aquatics. These plants prefer high humidity and can stand to be submerged for brief periods of time, but really prefer boggy conditions to living in a pond. Bogs tend to have rather poor, acidic soil, and plants cope with these conditions in a variety of ways. Particularly in the southeast, several types of plants take advantage of the plentiful populations of insects to provide supplemental nutrition to what little they manage to find in the soil. Pitcher plants and sundews are among the hardiest and most attractive of the lot. Some pitcher plants can stand three feet tall and are so colorful that some florists even use them in arrangements. Sundews tend to cling close to the soil but put on a sparkling show each morning. Plus both types of plants can take a bite out of the insect population that discovers your pond each summer!

Culture details: Various carnivorous pitcher plants that grow through the southern United States can actually withstand fairly severe winters. They make attractive compliments to any bog or pond, and require minimal protection in winter. A companion plant, the sundew, also prefers the same conditions. Some sundews reseed themselves, while others form a winter resting bud from which they spring forth when the weather warms up. These plants prefer moist acidic soil (such as peat or sphagnum moss) is best. Simply submerge the pots in shallower areas of your pond.

Final Thoughts
Extending your zone requires many of the same tools as regular gardening. You need good soil, mulch, a wall or fence, burlap, a good water-soluble fertilizer such as "Miracle Grow", and a plant vitamin and hormone formula to encourage rapid root growth, such as "Superthrive". Good soil, fertilizer and growth stimulants help a plant establish a strong root system. Since the plant is certain to face its first harsh winter within a few months of planting, it is critical that it be given every opportunity to become well established. Mulch can protect the roots both from summer heat and winter cold. A protected area such as a fence or wall provides a microclimate that can prevent temperatures from reaching the extremes experiences elsewhere in a garden, and provides extra growing time. Burlap is essential both to protect from the winter cold and the drying winds which can be especially damaging to a fragile plant stressed by other environmental factors. And most of all, be patient and persistent. Not all failures are due to temperature extremes. Plants that normally grow in warmer climates often take advantage of warm spells while the plants we are more familiar with remain dormant. Make sure these plants have what they need to grow (especially water) throughout the winter.