Silver inch plant

Identification and origin

Tradescantia zebrina belongs to the spiderwort family, Commelinaceae. Its native range runs from Mexico to Colombia across all of Central America: Guatemala, Belize, Honduras, El Salvador, Nicaragua, Costa Rica, and Panama. Grown around the world as an ornamental, it has naturalized in many tropical and subtropical regions and is considered invasive in Florida, where planting it in the ground is not recommended.

It is a tender herbaceous perennial with a creeping or trailing habit. Its succulent stems root at the nodes as soon as they touch soil. The plant rarely grows more than 6–9 in tall but spreads 12 in – 2 ft or more. Its alternate leaves are fleshy, ovate to lance-shaped and pointed, clasp the stem, and measure 1–3 in long. The upper side, green to purplish, carries two broad silvery stripes; the underside is a deep magenta-purple. Fine hairs line the leaf edges, and the leaf surface seems to sparkle in bright light.

The tiny flowers have three lavender to purple petals and yellow anthers and emerge between two boat-shaped bracts. They appear off and on in warm climates but rarely on indoor plants. The epithet zebrina means “zebra-striped”; the genus honors John Tradescant and his son, gardeners to King Charles I of England. It is still sometimes sold under its old names, Zebrina pendula or Tradescantia pendula. Among the cultivars, ‘Quadricolor’ is striped cream, pink, purple, and green, and ‘Burgundy’ has dark purple foliage.

Light

Indoors, give it bright light, ideally filtered: that is what keeps the silver stripes and purple tones. It tolerates direct sun if shaded from afternoon sun; sun that is too strong, especially in hot climates, washes out its colors.

It tolerates shade, but in low light the stems drop their lower leaves and stretch, and the leaves lose much of their color. If you move it outdoors for summer, wait until all danger of frost has passed and acclimate it gradually to outdoor light to prevent sunburn; outside, light shade suits it best.

Watering

During active growth, water regularly and generously to keep the mix moist, but let the surface dry between waterings. The pot must always drain: mix that stays soggy leads to root and stem rot.

From fall to late winter, during its rest period, cut back noticeably and let about two-thirds of the mix dry before watering again. It appreciates average to high humidity. Avoid wetting the foliage and crowding plants together, both of which encourage leaf spots.

Potting mix

A light, well-drained, soil-based potting mix is all it needs; loamy or sandy textures and acidic to alkaline pH are fine. Always use a pot with a drainage hole. During active growth, a balanced liquid fertilizer once a month keeps the foliage dense.

Temperature

Indoor temperatures of 64–75 °F suit it perfectly. Do not let it drop below 50 °F: this is a tropical plant that cannot take frost.

Outdoors year-round, it can only be grown in frost-free climates, USDA zones 9a to 11b, where it makes a groundcover. Elsewhere it is used in hanging baskets or summer containers, or simply moved outside for the warm months and brought back in afterward.

Repotting

Grow it in pots, hanging baskets, or at the edge of a shelf where its stems can trail freely. With age the plant inevitably loses its lower leaves and gets thin: rather than repotting an old clump again and again, renew it regularly from cuttings. When a pot of rooted cuttings gets crowded, move the whole group into a larger container.

Pruning

It takes hard pruning very well: cut it back firmly each year in very early spring if it has sprawled. Pinch the stem tips regularly for a fuller plant, and remove dry leaves at the base of the trailing stems. On variegated forms, remove shoots that have reverted to plain green. Wear gloves, since the sap can irritate skin.

Propagation

It could hardly be easier. In spring or summer, take tip cuttings about 3 in long and insert four to six together in a 3 in pot of well-drained mix. Keep them warm in bright, filtered light, with the mix barely moist: roots form in about two weeks. Cuttings also root readily in a glass of water, and no rooting hormone is needed. Layering works too, since the stems root at the nodes wherever they touch the soil.

Common problems

• Stems bare at the base: normal aging, made worse by low light. Rejuvenate the plant from cuttings.
• Dull leaves with faint stripes: too little light; on the other hand, sun that is too strong also washes out the colors.
• Long, spindly stems: not enough light, or no pinching.
• Stem or root rot: mix kept soggy.
• Spots on the leaves: fungal leaf spot, encouraged by wet foliage and crowded plants.
• Pests: aphids, mealybugs, scale, whiteflies, spider mites, thrips, and vine weevils.

The same symptom can have several causes: look at light, watering, and the condition of the stems together before acting.

Toxicity

Toxic, though of low severity, to both pets and people: the leaves and the watery, mucilaginous sap are the culprits. Chewed or swallowed, they can irritate the mouth and stomach of dogs, cats, and children. Simple contact can cause skin irritation and redness (dermatitis) in sensitive people. Wear gloves when pruning or taking cuttings, keep the plant out of reach of pets and children, and if any is swallowed, call your veterinarian or Poison Control.