How to Grow Snapdragons in Australia

Snapdragon (Antirrhinum majus) is a short-lived perennial in the plantain family, Plantaginaceae. Australian gardens grow it as a cool-season annual for bedding, pots and cut flowers. Squeeze the sides of a flower and the dragon opens its mouth, a trick few children can resist. The step most gardeners get wrong is burying the tiny seed, which needs light to germinate.

Three mistakes that matter

1. Burying the seed. Snapdragon seed needs light to germinate, so seed covered with soil often never comes up. Press it onto the surface of damp seed raising mix and leave it uncovered, as set out in Sowing Seeds.
2. Sowing into the heat. Snapdragons can stop flowering for a spell in very hot weather, and humid heat suits rust. Sow inside your zone's window in the table under When to plant, so the plants flower through the cooler months.
3. Wet, crowded leaves. Rust is the most serious disease of snapdragons, and it thrives on foliage that stays damp. Keep to the spacing in Sowing Seeds and water the soil rather than the leaves.

When to plant

Snapdragons flower best in cool, bright weather, so sow for flowers from late winter into spring. Autumn is the main window in most zones, and southern gardens can sow again from late winter. Seedlings come up in 7 to 14 days at a soil temperature of 21 to 24°C, so autumn trays are quick in warm soil.

For late-winter sowings, start the tray in a warm, bright spot or on a seedling heat mat.

Site, soil and setup

Give snapdragons full sun and fertile, free-draining soil rich in compost. They cope with part shade if they get at least 3 hours of direct sun a day. They prefer soil close to neutral, and heavy, sodden ground brings root rot.

Plant in a different bed from last season's snapdragons, and clear the old plants away, because they carry rust into a new crop.

Container growing

'Tom Thumb Mixed' grows to about 20 cm, so it suits pots, window boxes and the edges of tubs. Choose a container of at least 10 L with drainage holes, such as a 30 cm pot (about 13.5 L), filled with fresh potting mix. Bagged mix can carry Legionella bacteria: wet it first, wear a mask and gloves, and wash your hands afterwards.

• Watering: water at the base whenever the mix is dry a few centimetres down.
• Feeding: potted plants often need more feeding than beds. Give fish and seaweed blend at 25 mL per 9 L every fortnight, then liquid potash at the label rate once buds show.
• Position: full sun, moving pots to follow the sun as winter shadows lengthen.

Sowing Seeds

Raise snapdragons in trays and plant them out, which gives the tiny seed the steady moisture and light it needs.

Starting in trays

• Fill a tray with fine seed raising mix, firm it gently and water it before sowing.
• Mix the seed with a little dry sand and scatter it thinly over the surface.
• Press the seed onto the mix and leave it uncovered, or dust it with vermiculite, which lets light through.
• Cover the tray with glass or clear plastic to hold moisture, and mist it or water from below so the seed stays on top.
• Seedlings usually appear in 7 to 14 days.

Pricking out and planting out

• Move seedlings into cells or small pots once their first true leaves appear, usually 3 to 4 weeks after sowing.
• Harden off the young plants (stand them outdoors for a few hours, then longer each day, until they take full sun and wind).
• Plant out when they are 5 to 10 cm tall, at the spacing in the table below.
• Sowing direct works in fine, damp soil in mild weather, but the seed washes away easily; thin seedlings to the same spacing.

'Tom Thumb Mixed' is a dwarf snapdragon. Tall cut flower snapdragons are sown the same way, but they need wider spacing and a stake.

Care by growth stage

Snapdragons flower best when they are fed regularly, with even moisture at the roots and dry leaves. Switch to a potassium feed once the first spikes show.

Stake tall types at planting, before the spikes lean, and tie each stem loosely to its stake as it grows.

Deadheading

An early pinch and regular deadheading keep snapdragons bushy and flowering for longer.

• Pinch: at about 10 cm, pinch the tip back to a pair of leaves so side shoots carry more spikes, a few weeks later.
• Tall types for one long stem: skip the pinch and let the main spike run.
• Spent spikes: cut each one back to a pair of leaves or a side shoot once most of its flowers have faded.
• After the first flush: cut the plants back lightly and feed them, and a second flush often follows.
• Spotted leaves: remove leaves with rust while you deadhead, and put them in the bin rather than the compost.
• End of the season: pull out and dispose of old plants, as flowering usually declines after the first year and rust carries over.

Companion planting

Snapdragons share their autumn sowing months with most cool-season flowers.

Grows well with

• Violas and pansies: sown in the same months, they fill the front of the bed below the spikes.
• Calendula: another autumn sowing that flowers alongside in the same sun and soil.
• Cornflowers: upright blue flowers that suit a picking bed beside tall snapdragons.
• Sweet peas: grown on a trellis behind, for a second cut flower in the same season.

Keep apart

• Sunflowers: sown in the same autumn months in the subtropics, they soon tower over dwarf snapdragons and shade them.
• Nasturtiums: they sprawl over dwarf plants and smother them.

Harvesting Blooms

Cut a spike when the florets on its lower third have opened and the rest are still in coloured bud.

• Cut the longest stem you can, just above a pair of leaves, so side shoots follow.
• Strip the lower leaves and stand the stems in a clean bucket of water straight away.
• Keep the stems upright, because stems laid flat soon bend their tips upwards.
• Use the short stems of 'Tom Thumb Mixed' for posies and small jars.

Cut snapdragons often last 7 to 10 days in a vase. Most are sensitive to ethylene, the gas ripening fruit gives off, so keep the vase away from the fruit bowl. Snipping off the tight buds at the tip helps the rest of the spike open sooner.

Common problems

Seed does not come up. Seed buried too deep, the first point in Three mistakes that matter, is the usual cause, followed by mix that dried out. Read more

Seedlings collapse at soil level. Damping off (a rot of young seedlings, caused mostly by Pythium species and Rhizoctonia solani) strikes in wet, reused mix or dirty trays. Read more

Seedlings grow tall and pale. They are short of light, so move the tray into bright light as soon as the seedlings show. Read more

Flowering stops in hot weather. Snapdragons often pause in heat; keep watering and deadheading, and they usually pick up as the weather cools.

Pests and diseases

Rust is the disease to watch on snapdragons; the pests are the usual ones of soft, cool-season growth.

Snapdragon rust (Puccinia antirrhini). Pale yellow spots appear on the upper leaf with dark brown, dusty pustules beneath, and badly hit leaves shrivel. It has been widespread in Western Australia for decades and is worst in humid weather. Remove spotted leaves early and clear old plants, as set out in Deadheading.

Aphids (Aphididae). Small sap-suckers cluster on new shoots and under the leaves, leaving sticky honeydew. Hose them off with a firm jet, then spray insecticidal soap on colonies that return, and let ladybirds and lacewings do the rest. Read more

Grey mould (Botrytis cinerea). Ageing flowers turn brown and soft under a grey fur in cool, damp weather. Snip off affected flowers promptly and water at soil level.

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). They chew seedlings to the ground overnight and leave silvery trails. Hunt them by torchlight about two hours after sunset, set beer traps and ring pots with copper strips. Read more

Prevention first

• Clear fallen leaves and spent flowers from around the plants.
• Skip broad insecticide sprays, which kill the ladybirds and lacewings that eat aphids.
• Use fresh seed raising mix and clean trays for every sowing.
• Check the undersides of the leaves each week for rust pustules and aphids.

Tips

1. Sow a second tray about a month after the first to spread the flowers over a longer season.
2. A tray of snapdragons makes a good first project for growing from seed with children, because the seedlings show within a fortnight.
3. Watch the bees: they land on the lower lip and push the flower open to reach the nectar inside.