How to Grow Verbena in Australia

Garden verbena (Verbena × hybrida) is a tender perennial of the verbena family, Verbenaceae, grown as an annual for its clusters of small flowers. It blooms for months in pink, purple, red and white, filling beds, pots and hanging baskets through the warm season. Most failures happen before the first shoot: the seed is slow, and a cold, soggy tray rots it.

Three mistakes that matter

1. Sowing into cold, wet mix. Verbena seed takes three to four weeks to come up and dislikes excess moisture, so it rots in a chilly, soggy tray. Wait for warm soil, keep the mix damp rather than wet, and give it time.
2. Heavy soil and too much water. Roots rot in waterlogged ground, and plants that sit wet often collapse at the base in summer. Choose free-draining soil or a raised bed, and water only once the soil has dried below the surface.
3. Shade and crowding. In low light, or packed closely with still air, plants flower less and powdery mildew takes hold. Give them at least 6 hours of direct sun and the full spacing in Sowing Seeds.

When to plant

Sow when the soil holds 21 to 24°C, which suits spring and summer in the south and the drier, milder months in the north. Verbena is frost tender, so plant out only after the last frost. One sowing flowers for months, so most gardens need only one batch a year.

At the cool start of a window, sow in trays on a seedling heat mat or in a warm, sheltered spot. Sowings made after the window closes run into frost in the south or humid heat in the north.

Site, soil and setup

Verbena wants full sun, at least 6 hours of direct light a day, and soil that drains freely. It copes with acid and neutral soils, so pH seldom needs correcting, and it is fairly drought tolerant once settled.

Damping off fungi survive between crops on old plant material, so choose a fresh spot if seedlings collapsed there the year before. See water-repellent soil for more on sandy ground.

Container growing

Verbena suits pots, window boxes and hanging baskets, and a container lets you control drainage. Give each plant at least 10 L of fresh potting mix: a 30 cm pot holds about 13.5 L. Florist Mix, at about 30 cm tall and spreading, is the better choice to spill over a basket edge. Potting mix can carry Legionella bacteria, so dampen it before opening the bag, wear a mask and gloves, and wash your hands afterwards.

• Watering: pots dry out far faster than beds; water once the top few centimetres feel dry, and never let the mix dry out completely.
• Feeding: from the first flowers, water on fish and seaweed blend at 25 mL per 9 L every fortnight.
• Position: full sun all day if possible, with drainage holes clear and no saucer left full of water.

Sowing Seeds

Most gardeners start verbena in trays, because the slow seed is easier to watch there, though it can also go straight into warm soil.

Starting in trays

• Fill punnets with fresh seed raising mix and sow 5 to 6 mm deep.
• Water once, then keep the mix just damp, never soggy, in a warm spot.
• Expect seedlings in about 3 to 4 weeks, sometimes a little sooner at 21 to 24°C.
• Move seedlings to single cells when the first true leaves appear.
• Harden off the seedlings (stand them outside for a few hours of gentle light, lengthening the time daily for a week or two before planting).
• Plant out 25 to 30 cm apart at 5 to 10 cm tall. Water each one in with half-strength seaweed solution, 15 mL per 9 L.

Sowing direct

Rake a fine seedbed and sow 5 to 6 mm deep. Thin the seedlings to 25 to 30 cm apart once they are big enough to handle. Snails find direct-sown seedlings quickly, so check the row at night.

Both mixes are sown and grown the same way. Height is the difference, and it decides where each one goes.

Care by growth stage

Verbena is a light feeder, and water matters more than fertiliser: steady at first, then deep but occasional once plants are established. Keep water off the leaves, because damp foliage invites mildew and grey mould.

If growth stalls in thin, poor soil, scratch in a light dose of all-purpose controlled release granules (NPK around 14-5-10) at the label rate.

Deadheading

Garden verbena keeps flowering all season when spent clusters come off, and a light trim restarts plants that tire in midsummer heat.

• Every few days: snip faded clusters off just above a pair of leaves.
• At planting: pinch out the growing tips for bushier plants with more flowers.
• Midsummer: if flowering slows, trim the whole plant back by about a quarter of its height and spread.
• Near bushland: remove heads before seed drops, because verbena self-seeds; your council can say whether it is a local weed.
• Frost-free gardens: tidy lightly in autumn and cut back harder in spring as new shoots appear.
• Frosty gardens: pull out spent plants once frost ends the season and compost them.

Companion planting

Verbena mixes best with plants that share its full sun, dry feet and long summer season.

Grows well with

• Petunias: the same full sun, free-draining soil and basket life, with matching spacing.
• Lavender: wants the same lean, well-drained ground and little water once settled.
• Zinnias: sown into the same warm soil, they add height behind a verbena edge.
• Vegetable beds: verbena draws bees and butterflies, part of a pollinator garden.

Keep apart

• Zucchini and other hungry, thirsty crops: the rich soil and steady water they need keep verbena too wet.
• Sunflowers to the north of the bed: tall stems cast shade over low verbena for hours.

Harvesting Blooms

Cut stems for small posies when the outer ring or two of florets in a cluster have opened and the centre is still in bud.

• Pick early in the morning, when stems are fully charged with water.
• Carry a bucket of water and drop each stem in as you cut.
• Cut just above a pair of leaves, so the plant branches and flowers again.
• Pull off lower leaves so none sit in the water.

Keep cut stems somewhere cool and out of the sun until you arrange them. Change the vase water whenever it clouds or runs low. Cutting counts as deadheading, so every posy also feeds the display outside.

Common problems

Nothing comes up. Verbena usually needs three to four weeks, so be patient. Cold or soggy mix is the usual cause of a bare tray; see the first of the Three mistakes that matter. Read more

Seedlings collapse at soil level. Damping off, a rot caused mainly by Pythium species and Rhizoctonia solani, pinches young stems where the mix stays wet. Read more

Established plants wilt in moist soil. Root rot follows waterlogged ground or heavy watering; see the second of the Three mistakes that matter.

Flowers turn brown and furry. Grey mould (a Botrytis fungus) spreads through flowers in cool, damp weather, so pick off affected clusters and water at soil level.

Few flowers in midsummer. Heat and ripening seed slow new buds; the midsummer trim in Deadheading usually brings a fresh flush.

Pests and diseases

Verbena is fairly trouble free in sun and good drainage; most problems follow drought stress, shade or wet weather.

Powdery mildew (Golovinomyces species). A white, powdery film spreads over the leaves, worst on plants short of sun or stressed by drought. Remove badly affected leaves and spray 1 part full-cream milk to 10 parts water. Read more

Two-spotted mite (Tetranychus urticae). Fine yellow speckles appear on the leaves, worst underneath, and spread fast in hot, dry weather. Hose the undersides of the leaves on three mornings running, and water deeply so plants stay unstressed. Read more

Aphids (family Aphididae). Small sap-suckers crowd the soft tips and leave sticky honeydew. Wash them off with a firm spray of water, or wet the leaf undersides with insecticidal soap. Read more

Garden snail (Cornu aspersum). Snails and slugs chew seedlings at night, worst in wet spells and under heavy mulch. Hunt them by torchlight a couple of hours after dark, especially on rainy nights, and lay a shallow beer trap near the bed. Read more

Prevention first

• Plant in full sun and give each plant the full spacing from Sowing Seeds.
• Aim water at the soil early in the day, leaving foliage dry.
• Soak deeply in dry spells, because drought-stressed plants draw mites and mildew.
• Use new seed raising mix and clean trays for every sowing.

Tips

1. To keep a favourite colour from a mix, take a cutting of that plant, since cuttings grow true to the parent.
2. Purpletop (Verbena bonariensis and Verbena incompta) is a different plant: a tall, upright weed up to 2 m. Garden verbena stays low and spreading.
3. Lemon verbena (Aloysia citrodora) is a shrub in another genus, grown for lemon-scented leaves, and needs its own care.