How to Grow Salvias in Australia

Scarlet sage (Salvia splendens), mealycup sage (Salvia farinacea) and painted sage (Salvia viridis) are salvias of the mint family, Lamiaceae. All three are grown from seed for spikes of colour from late spring until frost, and the blue and painted kinds keep bees busy. The usual mistake happens on sowing day: burying seed that needs light.

Three mistakes that matter

1. Burying the seed. All three germinate best with light reaching the seed, so seed sown deep often never comes up. Press it onto the surface of damp mix and leave it uncovered, or barely covered for painted sage.
2. Planting out into cold ground. Scarlet and mealycup sage are frost tender and sit still in cold soil, and a late frost can kill them. Keep seedlings under cover until the last frost has passed in your zone.
3. Soggy soil. Salvias rot at the roots and base where water lies, and mealycup sage is prone to root disease in wet ground. Plant into free-draining soil or a raised bed, as set out in Site, soil and setup.

When to plant

Warmth decides the start: salvia seed comes up in about 5 to 15 days once the mix holds 22 to 26°C. Spring garden soil is rarely that warm, so outside the tropics start seed in trays indoors or on a seedling heat mat. One sowing usually carries a bed through the season.

In Melbourne and the cool zone, Melbourne Cup weekend in early November is the traditional signal to plant out frost-tender seedlings.

Site, soil and setup

Give salvias full sun, at least 6 hours a day. Scarlet sage also flowers in part shade and does best in a sheltered spot. All three want free-draining soil with some organic matter, and scarlet sage prefers it close to neutral, around pH 6.0 or above.

Damping off fungi survive between crops on old plant debris. Clear spent plants away, and use a fresh spot if seedlings collapsed there the year before.

Container growing

All three suit pots, and compact 'Blaze of Fire' also fits window boxes. Give each plant at least 10 L of potting mix; a 30 cm pot holds about 13.5 L. Bagged mix can carry Legionella bacteria, so wet it before opening, wear a mask and gloves, and wash your hands afterwards.

• Watering: soak the pot once the mix is dry a finger's depth down; summer pots can need it daily.
• Feeding: from the first buds, water on fish and seaweed blend at 25 mL per 9 L every fortnight.
• Position: the sunniest spot you have, with a heavy pot for the 90 cm stems of 'Blue Bedder'.

Sowing Seeds

Start salvias in trays for the longest season, or sow direct once the soil is warm and frost is over.

Starting in trays

• Sow 4 to 8 weeks before your last frost, into fresh seed raising mix.
• Press the seed onto the damp surface and leave it uncovered; give painted sage only enough mix to hold it in place.
• Water from below or with a fine mister, so the seed is not washed under.
• Keep trays at 22 to 26°C in bright light, and expect seedlings in 5 to 15 days.
• Move each seedling into its own cell or small pot once its first true leaves open.
• Harden off the seedlings (more time outdoors each day for a week), then plant out at 5 to 10 cm tall.

Water each transplant in with half-strength seaweed solution, 15 mL per 9 L. Space plants 20 to 40 cm apart, closer for compact scarlet sage and wider for the taller two.

Sowing direct

• Rake a fine, level seedbed after the last frost.
• Press 2 to 4 seeds onto the surface every 30 cm.
• Keep the surface damp with a fine spray until seedlings show.
• Thin to the strongest seedling at each spot once true leaves open.

The three share one method but differ in size and thirst.

Care by growth stage

Salvias are light feeders, and a bed dug with compost carries them most of the way. Water matters more: scarlet sage needs it steadily, while the other two cope with the soil drying between drinks.

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

Deadheading

Faded spikes left on a plant turn to seed and slow the next flush, so a weekly trim keeps salvias flowering until frost.

• Young plants: pinch out the tips of scarlet and mealycup sage in spring for bushier plants; flowering starts a little later.
• Scarlet sage: snip each faded spike back to the next pair of leaves.
• Mealycup sage: cut spent spikes to a leaf pair, and after a long flush trim the whole plant lightly to keep it compact.
• Painted sage: cut back faded stems to bring on fresh spikes.
• Seed for next year: leave a few painted sage stems to ripen, as the Tips explain.
• End of the season: pull out spent plants and compost them.

Companion planting

Salvias sit well beside other warm-season flowers that go out after the last frost and want the same sun.

Grows well with

• Marigolds: frost tender too, they go in at the same time in the same full sun.
• Zinnias: another after-frost annual for a cutting bed, in full sun and free-draining soil.
• Petunias: sown on the surface in warmth like salvias, they share pots and window boxes.
• Vegetable beds: 'Blue Bedder' and painted sage bring bees and beneficial insects into the patch.

Keep apart

• Mint: its runners take over a bed and crowd low salvias.
• Tall sunflowers on the sunny side: a row of them shades salvias for much of the day.

Harvesting Blooms

Cut mealycup sage once the bottom three or four flowers on a spike have opened, and painted sage when its bracts are fully coloured.

• Cut in the cool of the morning with clean secateurs.
• Take each stem at full length, just above a pair of leaves.
• Strip leaves that would sit under water, and stand stems in a bucket of water as you go.
• For drying, wait until painted sage bracts have stiffened a little.

To dry mealycup or painted sage, hang small bunches upside down in a dry, dark, airy room for about two weeks. Keep them away from the damp air of a kitchen, laundry or bathroom. Use fresh stems in small vases and the dried spikes in winter arrangements.

Common problems

No seedlings. Seed covered too deeply, or mix far below 22°C, is the usual cause; the first of the Three mistakes that matter covers the fix. Read more

Seedlings topple over. Damping off (a stem rot of young seedlings, mostly from Pythium species and Rhizoctonia solani) strikes seedlings in wet mix. Read more

Tall, pale, floppy seedlings. They are stretching for light, usually on a dim windowsill, and need the brightest spot you have. Read more

Scarlet sage wilts and browns. It is not drought tolerant, and dry soil in hot weather scorches it; water as set out in Care by growth stage.

Flowering slows. Old spikes setting seed hold back new ones; trim them as set out in Deadheading.

Pests and diseases

Salvias are seldom troubled for long: snails take seedlings, and sap-suckers build up in hot, dry weather.

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). They chew seedlings and soft shoots at night, most of all after rain, and leave silvery trails. Collect them by torch about two hours after sunset, and set beer traps nearby. Read more

Aphids (family Aphididae). Small sap-suckers cluster on new shoots and under leaves and leave sticky honeydew. Hose them off with a strong jet, or spray insecticidal soap onto the leaf undersides. Read more

Two-spotted mite (Tetranychus urticae). Leaves turn yellow and finely stippled, and numbers climb fast in hot, dry weather. Hose the undersides of the leaves and keep plants watered. Read more

Powdery mildew (Golovinomyces biocellatus). White powdery patches spread over the leaves, mostly in summer and autumn; it has been recorded on salvia in Queensland. Remove the worst leaves and spray 1 part full-cream milk to 10 parts water. Read more

Prevention first

• Give plants the full spacing from Sowing Seeds, so air moves between them.
• Water the soil, not the leaves, early in the day.
• Raise seedlings in new mix and scrubbed trays.
• Check shoots and leaf undersides once a week through summer.

Tips

1. Save painted sage seed at the end of autumn, once most bracts have fallen. Seed from a mixed planting may give mixed colours.
2. Painted sage self-sows where it is happy, so pull unwanted seedlings while they are small.
3. In frost-free gardens, scarlet and mealycup sage can live on as short-lived perennials; trim them back after flowering for another flush.
4. Plant a clump of 'Blue Bedder' where you can watch it: in south-east Queensland gardens, blue-banded bees are regular visitors to salvias.