Germination temperature
Germinates easily at 16-21 °C (61-70 °F); more slowly on a cool windowsill.
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Hollyhock seed germinates easily in mild warmth, but the plants are usually biennial and are often damaged by rust. This guide covers sowing, when to expect the first flowers, and how to keep rust under control.
Germinates easily at 16-21 °C (61-70 °F); more slowly on a cool windowsill.
Press the seed into the soil and cover only lightly, if at all.
Quick and fairly even in a warm propagator; slower and more uneven in cool soil.
No special light or dark requirement for germination; full sun for growing plants.
Not required. Nicking the seed coat can speed germination.
Both work. Hollyhocks form a long taproot, so sow in cells or pots and plant out young.
Hollyhock seeds are flat, notched discs of about 4 mm, carried in a ring-shaped fruit. Sow them dry. Only sow seed from healthy plants: rust spores can travel on the papery parts that surround the seed.
Optional. Some seed lots show seed-coat dormancy. In a laboratory study, untreated seed germinated without any pre-treatment, but mechanically scarified seed germinated faster and gave the most vigorous seedlings. Gently rub the seed between two sheets of fine sandpaper or nick the edge with a nail clipper, away from the embryo.
Not needed. Hollyhock has no cold requirement for germination.
Not needed. An overnight soak in room-temperature water does no harm if you want to see which seeds swell, but sow soaked seed immediately.
The RHS gives 16-21 °C (61-70 °F). A propagator or a warm room is ideal; on a cooler windowsill germination simply takes longer. In hot weather keep trays shaded so the surface does not dry out.
Press the seed into the surface and cover lightly with fine compost or vermiculite, if at all. Outdoors, sow groups of three or four seeds where each plant is to grow.
A free-draining seed compost in cell trays or small pots. One or two seeds per cell avoids root disturbance later.
Keep evenly moist but never waterlogged; seedlings in cold, wet compost rot easily.
Hollyhock does not depend on light or darkness to germinate, which is why a light covering works. Move trays into good light as soon as seedlings appear to keep them short and sturdy.
Germination is usually quick at 16-21 °C (61-70 °F). Scarified seed comes up faster and more evenly than untreated seed.
Plant out while the seedlings are still small, before the taproot circles the pot. Space plants about 60 cm (24 in) apart in full sun and fertile, well-drained soil. Dwarf mixes can go slightly closer, but leave room for air to move between the leaves.
In the first season most plants form a low rosette of large leaves and a deep root. This is normal for a biennial: the flower spike follows after a cool season.
The RHS describes hollyhocks as flowering in the second year after sowing, but some strains are grown as annuals and can flower in their first season if sown early. Plants that do not flower in year one will flower the next season.
Cause: hollyhock rust (Puccinia malvacearum), spread by airborne spores and favoured by wet or humid weather. It starts on the lower leaves and moves up. Fix: remove affected leaves early, space plants for airflow, water the soil rather than the leaves, and clear all dead leaves at the end of the season.
Cause: the fungus overwinters on basal leaves, in the crown and on wild mallows. Fix: grow hollyhocks as biennials and discard them after flowering, control common mallow nearby, and do not save seed from rusty plants.
Cause: slugs, caterpillars and flea beetles attack young plants. Fix: protect seedlings at night and check leaf undersides regularly.
Cause: wind and wet soil. Fix: choose a sheltered spot and tie each stem to a stake as it grows; dwarf strains need less support.
In cool climates sow in spring, or in autumn and overwinter young plants under cover to flower the next year. In the Indian plains, sow at the start of the cool season so that plants grow through the winter and flower before the heat; in hill areas spring sowing is common. Avoid raising seedlings through the monsoon, when humid weather favours rust.
Replace plants after a few years, or treat them as biennials, so that rust does not build up. Hollyhocks self-seed readily, so let a few healthy plants drop seed to provide replacements.
Use a soaker hose or water at the base. Overhead watering spreads rust spores and keeps leaves wet.
Hollyhock is listed as non-toxic to cats, dogs and horses, and the flowers are traditionally used as an edible garnish.
Sow the Hollyhock Dwarf mix for compact, colourful spikes that need less staking.
Some strains do if sown early, but hollyhocks are usually biennial or short-lived perennials and most flower in their second year. A plant that only makes leaves in its first season is normal and will flower the following season.
It is not required: the seed germinates readily at 16-21 °C (61-70 °F). Gently nicking or sanding the seed coat can make germination faster and more even.
Rust is hard to avoid completely. Remove spotted leaves early, give plants space, water at the soil, clear all old leaves after flowering, remove wild mallows nearby and replace plants every year or two.