English ivy

Identification and origin

Hedera helix belongs to the family Araliaceae. It is native to most of Europe, from Ireland and southern Scandinavia to the Mediterranean basin (Iberian Peninsula, Italy, the Balkans, Greece and the islands), and east to Ukraine, European Russia, the North Caucasus and Turkey. Planted around the world as an ornamental, it has naturalized in North America, Argentina, Mexico, Australia and New Zealand; across much of the United States it is considered invasive, smothering woodland understory plants and climbing into trees until they decline and die.

It is a woody evergreen vine that clings to any support with adventitious rootlets growing from the stems. It has two stages. The juvenile stage, the one most often seen, creeps or climbs: its glossy dark green leaves have three to five lobes, and it does not flower. Once well established, usually after about ten years, ivy switches to the adult stage: the branches become shrubby with no rootlets, and the leaves are unlobed, oval to diamond-shaped. These branches bear umbrella-like clusters of small, nectar-rich, greenish-yellow flowers in late summer and fall, followed by black berries that ripen over winter and into the next spring. A climbing ivy can eventually reach 19.5–78.5 ft tall; as a groundcover it stays 6–9 in high but spreads without limit. There are hundreds of cultivars, with miniature, bird’s-foot, heart-shaped or curly leaves, or leaves variegated with white, cream or yellow (‘Glacier’, ‘Goldchild’, ‘Duckfoot’, ‘Needlepoint’ and many more).

Light

Indoors, most cultivars grow best in bright light without direct sun, which can scorch the leaves: near an east, west or north window, or set back from a south window. Ivy tolerates lower light, but then grows more slowly and variegated forms turn green; if the variegation fades, move the plant closer to the light. It can also be grown under artificial light. Outdoors, it grows equally well in full sun and deep shade.

Watering

Water thoroughly, then let the top few centimeters of mix dry before watering again, without ever letting the root ball dry out completely. The warmer the room, the faster the mix dries, so let observation, not the calendar, tell you when to water. Always empty the saucer: ivy left standing in water ends up with root rot. Rainwater is ideal, but tap water is fine. In the ground it tolerates some drought once established, but it has the best foliage in evenly moist soil.

Potting mix

A good houseplant potting mix or a peat-free multipurpose or loam-based mix, in a pot with good drainage. Ivy is not a heavy feeder: a foliage houseplant fertilizer once a month while it is actively growing is plenty, and none when growth stops, in summer heat or in cool conditions. Yellowing between the veins can signal a nutrient deficiency; in that case, apply a general-purpose liquid fertilizer at the dilution on the label. In the garden it tolerates almost any soil that is not waterlogged and prefers rich soils on the alkaline side.

Temperature

Ivy likes it cool: indoors it does well at 50–70 °F during the day, with slightly cooler nights. The warm, dry air of heated homes favors spider mites; cooler temperatures and more humid air help keep these pests down, at the cost of slower growth. It prefers moderate humidity but tolerates the low humidity of most homes; a tray of wet pebbles helps. Give it good air circulation and do not crowd the pots. Outdoors it is hardy in USDA zones 4a to 9b; in cold regions it benefits from a spot sheltered from winter wind and sun.

Repotting

Ivy can often stay in its nursery pot for a year or two. Repot when the plant becomes top-heavy, when roots fill the pot or poke out of the drainage holes, or when the root ball dries out too fast. The new pot should be only about 1 in wider than the old one: an oversized pot keeps the mix wet too long and leads to root rot. If the plant gets too big, it can also be planted out in the garden.

Pruning

Start training it while it is small: pinch the stem tips often to make a bushy plant, and cut back overly long shoots when it gets straggly. Remove at the base any shoots that revert to all green on a variegated cultivar, or to ordinary ivy leaves on a cultivar with unusual leaves. It is easy to train over a wire hoop or frame to make a topiary, as long as it is trimmed often. In the garden, trim back excess growth in mid-spring; an overgrown ivy can be cut back hard in early spring and regrows readily from old wood. Regular pruning keeps it in the juvenile, non-flowering stage. Wear gloves and long sleeves, because the sap irritates skin.

Propagation

Very easy. Stem or tip cuttings often root in a plain glass of water. You can also insert semi-ripe stem sections with at least two leaves into a free-draining mix in late summer, cover them with a plastic bag and keep them in bright light out of direct sun, removing the bag once new growth appears. Layering works just as well: pin a stem onto a pot of moist mix and sever it once it has rooted. In the ground, stems root on their own at the nodes, and birds spread the seed.

Common problems

One symptom can have several causes: check watering, heat, light and the leaf undersides before treating.

• Spider mites: a major problem indoors, worth checking for regularly, and favored by warm, dry air. Spray the foliage with water often, raise the humidity and keep the plant cool.
• Aphids on soft new growth, mealybugs, scale insects and whiteflies: cut out heavily infested parts and wash the plant by dunking the foliage upside down in water with insecticidal soap, with the soil covered by plastic.
• Leaf spots caused by bacteria or fungi: not serious; remove affected shoots and avoid wetting the foliage.
• Root rot: slow-draining mix, watering too often, a pot that is too large.
• Loss of variegation: too little light, or shoots that have reverted to green.
• Yellowing between the veins: a possible nutrient deficiency.
• Outdoors: cankers, stem rot and powdery mildew; ivy also creeps into gutters and damages paint, loose mortar and siding if it is not kept in check.

Toxicity

Toxic to pets and people. All parts of the plant contain triterpenoid saponins (hederagenin), concentrated mostly in the leaves, which are more toxic than the berries, along with polyacetylene compounds. In dogs, cats and horses, eating the plant causes digestive upset: drooling, vomiting, abdominal pain and diarrhea. In people, swallowing it can cause a burning throat, vomiting and abdominal pain and, in severe cases, hallucinations, delirium or convulsions. Simple contact with the sap gives some people redness, itching and blisters. Wear gloves when handling it, keep it out of reach of children and pets and, if it is swallowed, call Poison Control or your veterinarian.