Monday, July 7, 2008

Wild and Wonderful Ivy

Most of us think of ivy as a rampant but boring evergreen ground cover. But look closer and you’ll find a plant with a myriad of interesting variations that can not only provide mass ground cover, but also elegance and curiosity as a potted, trellised or even bonsai plant. Plants in the genus Hedera (Latin for ‘ivy’) are characterized by twining vines with aerial roots that assist them in their ascension.

Ivies are woody plants that spread out until they find something that lets them spread up. When they climb they attach themselves via root-like hold fasts. Ivy can cover slopes, chain link fences and is in fact a plant of choice used to cover massive sound barriers along interstate highways. As a vine for growing in shade, it is unsurpassed. If you want ivy to grow on a structure, fasten it as desired, then watch it go. As far as price per square foot is concerned, ivy is notably inexpensive.

All Hedera, regardless of species, have many things in common. Its foliage is alternate, 3-5 lobed or entire, often variegated. There are various cultivars and growth habits. The leaves range in color from creamy white to deep green with uncounted natural and hybridized variations. It produces umbels of tiny, 5-lobed greenish flowers followed by berry-like fruits in fall. The fruits are toxic to humans but not to animals.Hedera have two distinct growth phases. A young, juvenile plant often has lobed, minutely hairy leaves, adventurous rootlets, and climbs. The older, mature plant has larger, mainly broadly ovate leaves without lobes. Mature plants produce flowers and fruits. This latter phase is seldom seen when the plant is grown indoors. Mature unlobed ivies grown vertically often produce lobes, so pay attention if that is a concern of yours. Lobing is also affected by seasonal variation. This plant mutates readily and is generally hardy to USDA climate zone 5. Zones 6-10 are ideal. Climate zones 7-10 are best for variegated cultivars. Your nearby Cooperative Extension Service office can help you determine your soil pH by a very inexpensive soil sample.

They can live in bright to low light, but variegated forms require higher light, turning greener in low light. They tolerate average to dry conditions but must be well watered during extending dry spells. In addition, the soil must be well drained and completely dried out between irrigation cycles or ivy will get root rot. Hedera prefers humid climates but will tolerate average humidity.

While ivy grows in full sun, exposure to wind can cause leaf burn. It's ideal for shady gardens because it thrives in dark shade. Ivy makes an extensive root system that is tough and deep. Digging it out is a real chore. But, if you decide to remove an established plant it will not return from roots left in the ground once the major stems and leaves have been eliminated.

Be careful when deciding whether to plant ivy outdoors; the same qualities that make them a quick solution for covering up "problem areas" in your garden can make them quick weeds. The very characteristic that makes it a fine ground cover can render it unwelcome: it covers ground. Ivy can be troublesome if completely unchecked, but it’s nothing like kudzu. Ivy does not damage trees or sound structures. It isn't a parasite. It cannot harm a mature tree, but it could outlive it and therefore give the impression that it's killing it when actually the tree is just old. It cannot collapse a sound building. If it’s not pruned it can get into gutters or under shingles and dislodge them under its own weight. A mass of ivy can pull off stucco that's old or not firmly attached, but the plant itself will not do structural damage. In fact, it can protect a building from weather and provides extra insulation.

There are many Hedera species and I am going to describe 6 of them. The ones most common in the U.S. are the first three in the list, H. helix, H. canariensis, H. colchica.

Helix, which means "twining", refers to the way the ivy leaf attaches to the stem. H. helix has several subspecies (helix- English ivy, hibernica- Irish ivy, poetarum-Italian ivy, to name a few) but in general any ivy that starts with “H. helix” is often called English ivy. Brought to North America by colonial settlers, this plant grows easily in many types of soil and in sun or shade and is hardy from Zones 5-9. English ivy is fairly drought-tolerant once it is established. Its two to four inch leaves are alternate and simple or entire (unlobed). Juvenile plants’ leaves have 3-5 lobes and adult leaves are ovate to rhombic (diamond-shaped). Mature plants bear pale green flowers and produce berry-like fruit in fall clusters. English ivy can out-compete grasses, herbs and trees because it is a vigorous climber. In the south, H. helix can grow throughout the year. It mounds up to 1’ tall and climb up to 50’.

H. canariensis (African ivy, Algerian ivy, Canary Island ivy, Madeira ivy or Elephant Leaf ivy) is native to north Africa and the Iberian peninsula. It is distinguished by red leaf stems and 4-8” long heart-shaped or 3-lobed glossy emerald-green leaves. A variegated form is also available. A vigorous climber, this tropical or sub-tropical plant is damaged if temperatures fall below 20F (-6.6C). Growing only in Zones 8 - 10, it is adaptable to various soils and pH, but prefers rich, moist soil in partial sun to shade. It establishes and grows rapidly. If you live in Zone 7 or cooler, African ivy makes a good houseplant.

H. colchica (Persian ivy or Colchis ivy) is native to Asia, Georgia, Russia, northern Turkey and Iran. It's hardy to USDA climate zone 5 or 6 through 9 or 10. Foliage is 3-8” long, dark green, heart-shaped, leathery. When crushed the leaves are refreshingly aromatic.

H. rhombea (Japanese ivy) is native mainly to Japan and Korea. In the U.S. it thrives in Zones 6-9. Characterized by unlobed ovate or triangular leaves only 2" long, Japanese ivy is generally expensive and hard to find.

H. azorica is native to the Azores and thus known only as Azores ivy. Fan-shaped light green leaves grow 3" long on this fast climber. New growth is white and hairy.

H. nepalensis, or Nepal Ivy, has elliptic lobes with 3-6 “teeth.” Native to Himalayas, Afghanistan and western China, it has weak vigor.

I love ivy because it can be elegant, whimsical or purely functional depending on the variety. Fortunately, my Hedera wish list is almost complete. Here are my favorites so far:

H. helix ‘Baltica’- Flat, green, palmate foliage is more heart-shaped and has white veins. Grows in Zones 5-9.

H. helix 'Gold Child'- Variegated flat, palmate green leaves are splashed with gray and broad green-gold margins. Hardy from Zone 5 to 9.

H. helix 'Needlepoint'- Its delicate willowy leaves are under 1" long and look like a bird’s foot, but is hardy from Zone 5 to 9.

H. helix 'Telecurl'- Grows in Zones 5-9 and has a green ruffled leaf is curled between 5 lobes.

H. helix 'Anne Marie'- Variegated flat, hand like leaves have creamy colored lobes.

H. helix 'Ivalace' aka ‘Wilson’- Rippled 5 lobed dark green leaves have crimped margins that curve upward. Hardy in Zones 5-9.

H. helix ‘Teardrop’- 2002 Ivy of the Year. Mostly unlobed foliage that elongate to a point. Slow growing and stiffly branched. Has survived - l5 degree F temperatures.

H. canariensis Gloire de Marengo'- Zones 6-9. Heart-shaped or triangular foliage with wide white margins and grayish centers.

H. colchica 'My Heart'- It's hardy in USDA climate zones 5 - 10.  Needs some shade in zones 7-10.  You'll love its particularly large, green heart shaped leaves.

H. colchica 'Dentata Variegata'- won three awards from the Royal Horticultural Society (1907, 1979, and 1984). Large triangular leaves with a green center and light green edge have sharper points than usual at the end of its lobes. Hardy from Zones 6-9 and can take greater cold than ‘Gloire de Marengo’.

Hedera can be rooted in water using a stem or the tip cuttings of juvenile growth. A hormone to encourage growth works well too. While cuttings can be easy to do, finding the variety you want can be difficult. If you purchase an established plant, plant it in well drained soil just deep enough so that the root ball is flush with the surrounding earth. Let the soil completely dry between watering. Plant them 18” apart or more and they’ll fill in the space quickly. The original plants are considered mature after 2 years and can be thinned. If you’ve working in a small area that might be the best thing to do, but if you’re in a large space, thin what you need to keep it manageable. But how do you keep this plant manageable?

Cutting is successful with persistence but does not kill the plant. However, the use of cutting and then applying an herbicide may provide better control. Digging or pulling a plant up provides immediate control with little re-growth, but don’t leave the pulled plants on the ground; they can root and continue to grow.

Control Hedera that is growing up trees by cutting the vine at waist height, loosening the vine around the limbs and removing the roots. If the root can not be removed by hand, strip the bark and notch the exposed section of the vine. Paint on an undiluted herbicide such as glyphosate.

Hedera can have various pests and problems. Avoid the most common (root and stem rots and leaf spot) by not over irrigating. If you’ve got a rampant leaf spot problem use a fungicide. Spider mites are the most serious pests, usually on plants grown indoors. Treatment requires pesticides that are specifically developed for spider mite control (miticides or acaricides). Because most miticides do not affect eggs, a repeat application at an approximately 10- to 14-day interval is usually needed for control. Aphids can be controlled chemically, but also tend to kill other good bugs in the area. Try spot treatment first. Mealybugs have never destroyed ivy, but if they bother you try using the thumb and forefinger. If they’re really doing damage try Malathion. Whiteflies; I hate them but they’re easy to control. If your ivy is grown inside, try a white fly trap. If the ivy is outside an insecticidal soap is the least toxic material that can also get rid of them.

To sum up:
  • Plant Hedera at the same level it grew previously; don’t bury it.
  • Plant 18” apart.
  • Let the ground dry between irrigations.
  • Hedera is typically hardy between Zones 5-9.
  • Monitor the borders of the desired growth area to prevent escape.
Whether inside or out, Hedera is a wonderful plant with many potential applications. With a little love and care, this is a plant that will grow where and how you want it. Take some time to examine ivy varieties; you’ll be surprised at all Hedera have to offer.

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