How to Grow Hollyhocks in Australia

Hollyhock (Alcea rosea) is a cottage-garden flower in the mallow family (Malvaceae), grown for tall spikes of large, satiny flowers. Most strains live as biennials or short-lived perennials. They make leaves in the first year and flower the next summer on stems 1.5 to 2.5 m tall. They suit cool and temperate gardens best, and the usual mistake is letting rust run unchecked until it strips the leaves.

Three mistakes that matter

1. Moving a big plant. Hollyhocks grow a long taproot early, so a plant lifted late or left to fill its pot often wilts and stalls. Sow in deep single pots or where the plant will flower, and plant out while small.
2. Letting rust carry over. Hollyhock rust lives on through winter in old leaves, stalks and nearby mallow weeds, then infects the new growth in spring. Pick off the first spotted leaves, pull mallow weeds and clear away rusty stalks after flowering.
3. Skipping the stake. A 2 m spike in full flower catches the wind like a sail and snaps or topples. Drive in a stout stake at planting, clear of the crown, and tie the spike to it as it grows.

When to plant

Seed germinates best at 18 to 22°C, though outdoor sowings can go ahead in soil from about 10°C. For flowers next summer, sow from late summer into autumn. In the south, finish around Anzac Day so young plants settle before winter. 'Summer Carnival' sown early in spring can flower in its first summer. One sowing is enough, then sow again every year or two, because plants are short-lived (see annuals, perennials and biennials).

At the hot end of a window, raise pots in bright shade and plant out once the weather cools. Where winters are hard, keep late autumn sowings under cover until their first true leaves open.

Site, soil and setup

Plants usually live 2 to 5 years in one spot, so choose a position that is not dug every season. When plants need replacing, sow the new ones in a fresh bed away from the old rusty ground. For more on soil, see soil pH and preparing a garden bed.

Sowing Seeds

Start hollyhocks in deep pots or sow them where they are to flower, because both spare the taproot.

Starting under cover

• Fill deep single pots or tubes with fresh seed raising mix.
• Sow two seeds per pot, 10 mm deep, and later snip off the weaker seedling.
• Cover the pots with plastic film pierced with a few holes, and water with a spray bottle so the mix stays moist.
• Keep them at the temperature under When to plant. Seedlings appear in 2 to 3 weeks.
• Take off the film as soon as seedlings show, and give them full light.

Sowing direct

In mild weather, sow two or three seeds 10 mm deep at each spot, 40 to 60 cm apart, and thin to the strongest. Direct sowing suits cool and temperate gardens, where hollyhocks also self-sow readily.

Transplanting

Plant seedlings out 4 to 6 weeks after sowing, before roots crowd the pot. Harden them off first (a week or so of gradually longer spells outdoors that toughens soft growth), as in hardening off seedlings. Set each stake as you plant, 40 to 60 cm apart, and water in with seaweed solution at 30 mL per 9 L.

Care by growth stage

Steady moisture while young, dry leaves and a modest feed decide how tall and clean a hollyhock grows. Water at the base in the morning, because rain and splashing water carry rust spores from leaf to leaf.

Weeks count from sowing. Autumn sowings stay as a leafy clump over winter, while 'Summer Carnival' sown in early spring can go straight to the spike. Each spring, spread a 5 cm layer of compost around established plants, clear of the crown. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in at planting can help.

• Tie the spike to its stake with soft ties as it grows, adding a tie with each new stretch of stem.
• Along a fence, tie spikes to the palings or to a wire run between posts.
• Check ties after strong wind and loosen any that cut into the stem.

Cutting Back

Cutting back keeps rust from building up and tidies plants between flowerings. Clean tools after cutting rusty growth.

• Pick off the first rust-spotted leaves in spring as soon as they appear, and bin them.
• Remove badly rusted lower leaves through summer.
• Once the flowers fade, cut each spike to the ground and clear away the stalk and fallen leaves.
• To save seed, leave one or two spikes until the seed cases turn brown, then cut them.

Companion planting

Hollyhocks belong at the back of a border, along a paling fence or at the sunny end of a vegie patch.

Grows well with

• Calendula and cornflower, low enough in front to hide bare lower stems without crowding the crown.
• Vegetable crops, which gain from the bees the open flowers draw.
• Fence and wall plantings, which shelter the spikes from wind.

Keep apart

• Mallow weeds (Malva species), which carry the same rust and shelter harlequin bugs.
• Lavatera and other ornamental mallows, which the same rust attacks.
• Small sun-loving plants on the shady side, where tall spikes block their light.

Harvesting Blooms

Cut a spike for the vase when about a third of its flowers have opened.

• Pick early in the morning, when stems are full of water.
• Stand the stems in a bucket of water straight away.
• Strip the leaves that would sit below the waterline.
• Turn each hollow stem upside down, fill it with water and plug the end with a little cotton wool.
• Pull off faded flowers in the vase so the upper buds open.

Cut spikes usually last 7 to 10 days in a vase. For seed, snip the brown seed cases, dry them upside down and shake out the seed. Store it in a labelled envelope inside an airtight container in the fridge, and sow it the next season.

The petals are edible and add colour scattered over a salad or used as a garnish. Eat only flowers from plants that have not been sprayed.

Common problems

No flowers in the first year. Most hollyhocks are biennial and spend their first season making leaves; see When to plant for the sowings that flower soonest.

Seeds did not come up. Mix that dried out or stayed cold is the usual cause. Read more

Wilting after planting out. The taproot was disturbed, as under Three mistakes that matter; next time, plant out before roots fill the pot.

Plants fading after a few years. Hollyhocks are short-lived and build up rust with age, so raise replacements from seed or keep a few self-sown seedlings.

Pests and diseases

Rust is the most common hollyhock disease, and sap-sucking bugs and mites come next.

Hollyhock rust (Puccinia malvacearum). Yellow to orange pustules appear under the lower leaves first, with bright spots on the upper surface, then spread upward in humid weather. Badly rusted leaves yellow and drop, though plants are rarely killed. It lives on through winter in old growth and mallow weeds, so start with the hygiene under Cutting Back. On plants that rusted before, dust with sulphur as a preventive from early spring, never above 30°C.

Harlequin bug (Dindymus versicolor). These red and black bugs, about 12 mm long, cluster on soft growth, and their feeding makes growing tips wilt. Knock them into a bucket of strong soapy water and remove the mallow weeds where they breed. Read more

Two-spotted mite (Tetranychus urticae). Feeding leaves yellow stippling, mostly under the leaves, and numbers rise quickly in hot, dry weather. Avoid broad insecticides, which kill the ladybirds and predatory mites that keep them down. Read more

Slugs and snails (Gastropoda). They chew young leaves and can strip seedlings soon after planting out. Check under leaves and around rocks where they shelter by day, and set shallow beer traps dug slightly into the soil. Read more

Prevention first

• Space plants 40 to 60 cm apart in full sun so leaves dry quickly.
• Check the undersides of lower leaves each week from early spring, when rust and bugs first show.
• Clear loose timber, boards and litter from around beds, where harlequin bugs and snails shelter, as in garden hygiene.
• Pull mallow weeds along fence lines and paths as well as in the bed.

Tips

1. Lift self-sown seedlings while they are small if you want them somewhere else, before the taproot runs deep.
2. Seedlings from a mixed planting may not match their parents, so keep seed only from the colours you like best.
3. Set 'Henry the Eighth' Black against a pale wall or among pale flowers, where its dark flowers show up.