How to Grow Stock in Australia

Stock (Matthiola incana) belongs to the cabbage family, Brassicaceae. It is grown for its spikes of sweetly scented flowers, in the bed and the vase. Across most of Australia it flowers from autumn through winter into spring, and a few stems can scent a whole room. The usual failure is timing: plants sown into warming weather make leaves, then fade before they flower well.

Three mistakes that matter

1. Sowing into warming weather. Stock flowers best in cool conditions, and plants that meet hot days and warm nights before they bloom decline and flower poorly. Sow from late summer into autumn, within the months for your zone in When to plant.
2. Planting into acid soil. Like the rest of the cabbage family, stock does not thrive in acid ground. Check the pH and dig in lime four weeks before planting, as Site, soil and setup describes.
3. Crowding plants and wetting the leaves. Tight, damp foliage invites downy mildew and grey mould, which both thrive in cool, wet weather. Give each variety its full spacing from Sowing Seeds, and water the soil rather than the plant.

When to plant

Stock seed germinates at about 18 to 24°C, yet the plants grow and flower best in cool weather. Sow as the summer heat breaks, so seedlings establish in warm soil and flower through the cool months. For a longer run of stems, sow a few seeds every few weeks through your window.

Near the end of a window, choose 'Dwarf Ten Week Mixed', which flowers sooner than the giant types. Evening scented stock (Matthiola longipetala, sold as Matthiola bicornis) germinates cooler, at about 14 to 20°C, so it can go in later.

Site, soil and setup

Give stock full sun, at least 6 hours of direct sun a day, in a bed sheltered from strong wind. It wants deep, rich soil that drains freely and sits neutral to slightly alkaline, about pH 7.0 to 7.5.

Downy mildew spores survive in old leaves in the soil. Move stock to a fresh bed each year, returning after 2 to 3 years.

Container growing

'Dwarf Ten Week Mixed', 'Evening Scented' and 'Virginian Mixed' are the compact choices for pots. One plant needs a pot at least 20 cm wide and deep, which holds about 5 L. A group needs 10 L or more, such as a 30 cm pot of about 13.5 L.

Fill it with fresh potting mix. Bagged mix can carry Legionella bacteria, so wet it before you handle it, wear a mask and gloves, and wash your hands afterwards.

• Watering: water at the base once the top 5 cm of mix is dry, soaking it through.
• Feeding: fish and seaweed blend at 25 mL per 9 L, fortnightly, then liquid potash at the label rate once buds show.
• Position: full sun, though a few hours of shade suits pots in warmer spots.

Sowing Seeds

Garden stock is usually raised in trays and planted out. Evening scented stock and Virginian stock (Malcolmia maritima, a separate genus) grow in much the same way, but are sown where they will flower.

Starting under cover

• Sow thinly over fresh seed raising mix in a clean tray or punnet, and cover with 3 mm of fine mix.
• Keep the mix moist but never wet or dry.
• Hold the tray at the germination temperature in When to plant, and expect seedlings in 1 to 2 weeks.
• When the first true leaves open, prick out the seedlings (move each into its own cell or small pot).

Sowing direct

• Rake the soil fine, scatter the seed thinly and cover it with 2 to 3 mm of soil.
• Keep the surface damp until seedlings show, usually within 1 to 3 weeks.
• Thin Virginian stock to 15 cm apart and evening scented stock to 20 to 30 cm.
• Leave evening scented stock where it comes up, because it does not take kindly to being moved.

Due to quarantine restrictions and our shipping policy, we cannot send 'Evening Scented' stock seed to South Australia or Western Australia.

Transplanting

• Plant out when seedlings are 5 to 10 cm tall, usually 5 to 10 weeks after sowing.
• Harden off the young plants first (get them used to outdoor sun and wind by leaving them out a little longer each day).
• Space them as the variety table below gives, with the lowest leaves sitting level with the soil.
• Water in with seaweed solution at half strength, 15 mL per 9 L, then mulch lightly.

Care by growth stage

Cool nights, steady moisture and a potassium-rich feed from bud stage decide how well stock flowers.

Deadheading

Take off spent spikes as they fade, which on the dwarf types can bring more flowers.

• How to cut: cut each faded spike back to just above a set of leaves, using sharp snips or secateurs.
• Giant types: the main spike is the crop, and once it is cut the plant is usually finished.
• No pinching: leave the growing tips of garden stock alone.
• Virginian stock: let a few seed pods ripen, and seedlings may come up by themselves.
• End of the season: pull plants out once warm weather stops the flowers, and add them to the compost heap.

Companion planting

Good neighbours share its cool season and its need for sun, without shading it.

Grows well with

• Violas and sweet William: low cool-season flowers sown in the same months, set in front of taller stock.
• Calendula: another annual of the same sowing window, adding orange and yellow.
• Cornflowers: sown in the same months, and a blue partner for stock in the vase.

Keep apart

• Cabbages, broccoli and kale: they share cabbage aphid and cabbage white caterpillars with stock.
• Peas on a trellis to the north: their winter shade falls across plants that need 6 hours of sun.

Harvesting Blooms

Cut stems for the vase when one-third to one-half of the flowers on the spike are open.

• Cut the longest stem you can with sharp snips, and strip the lower leaves.
• Stand each stem in a clean bucket of water straight away.
• Cut off any thick, white, fibrous base, which stops the stem taking up water.
• Change the vase water and recut the stem ends often.

Cut stock usually lasts 7 to 10 days in a vase. Stems keep for a short time at 2 to 5°C, though long chilling costs some of their scent. Use them in vases, posies and table arrangements.

Common problems

Plants fade before they flower. Warm weather is the cause; see the first point in Three mistakes that matter.

No seedlings appear. Mix that dried out, or seed buried deeper than 3 mm, is a common cause. Read more

Seedlings topple over. Damping off (a seedling rot at the soil line, mostly from Pythium species and Rhizoctonia solani) is favoured by wet mix. Read more

Stems flop. Too much nitrogen gives weak stems, so ease off leafy feeds and switch to potassium at bud stage.

Leaf tips and edges turn brown at flowering. A shortage of potassium is a common cause; feed as the flowering row in Care by growth stage sets out.

Mostly single flowers. Many mixed packets give both single and double flowers; see Tips for sorting seedlings.

Pests and diseases

Aphids and caterpillars are the usual pests, and cool, damp weather brings the moulds.

Cabbage aphid (Brevicoryne brassicae). Grey-green aphids gather in colonies coated with a whitish powder, mostly under the leaves. Check leaf undersides often and spray insecticidal soap. Read more

Cabbage white butterfly (Pieris rapae) and diamondback moth (Plutella xylostella). Their caterpillars chew holes in the leaves, worst in autumn and spring. Check the leaves often, and net young plants with fine insect mesh at planting. Read more

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). They eat tender leaves and seedlings at night, leaving slime trails. Collect them by torchlight, set traps and clear their hiding places. Read more

Downy mildew (Hyaloperonospora parasitica). A white, fluffy growth forms under the leaves, which yellow and drop, mostly at 8 to 16°C. The strain on stock does not cross to broccoli or cabbage. Remove affected leaves and thin crowded plants. Read more

Grey mould (Botrytis cinerea). Ageing flowers go soft and grey, mostly in cool weather with heavy dew. Cut off affected spikes.

Prevention first

• Keep to the spacing and watering in Three mistakes that matter.
• Pull cabbage-family weeds such as wild radish, which harbour cabbage aphid.
• Clear away spent flowers and dead leaves, where mould and mildew spores survive.
• Start every sowing in fresh mix and clean trays.

Tips

1. To favour double flowers, chill the tray at 4 to 7°C for 3 to 4 days at the seed-leaf stage. Keep the paler, lighter green seedlings and discard the darkest, which usually flower single.
2. Plant a few stock by a bedroom window or a back door, since the scent is strongest in the evening.
3. Scatter evening scented stock seed among sturdier annuals, whose stems help hold up its slender ones.