How to Grow Hollyhocks

How the biennial cycle works

Old-fashioned hollyhocks (Alcea rosea) take two seasons to complete their life. In the first year they put down roots and grow a low rosette of large, lobed leaves. The next summer they send up tall spikes, bloom, set seed and usually die. Some newer varieties are short-lived perennials that last a few years.

Hollyhocks reseed readily, so a planting that is allowed to drop seed keeps itself going. South Dakota State notes that letting several plants set seed each year usually ensures some plants bloom every summer. You end up with a mix of flowering plants and first-year rosettes, like the patches along old farmhouse foundations.

Site

Give hollyhocks full sun, at least 6 hours a day, though light shade is tolerated. Choose somewhere sheltered from strong wind, because the flower stalks reach 4 to 8 feet. Along a fence, wall or building is the classic spot, and it gives the stalks something to lean on. They do best in moist, well-drained soil. NC State prefers sandy to clay loams rich in organic matter, and Cornell warns that rich soil makes plants more likely to need staking.

Plant them at the back of a border where their height won’t block shorter plants. Leave room for air to move around them, which matters a lot for disease.

Planting

You can start hollyhocks from transplants or seed.

Transplants: South Dakota State says buying potted plants is the easiest way to add hollyhocks. Set them 12 to 18 inches apart in a sunny spot and keep them well watered until they’re established. Because the patch spreads as plants drop seed, consider leaving 3 to 4 feet for it to fill out over a few years.

Seed: Sow outdoors in early spring or any time through summer. Cornell’s cutoff is about two months before your first heavy fall frost. Don’t cover the seed, because light helps it germinate. Keep the surface moist, and expect seedlings in 10 to 14 days. Plants from these sowings bloom the following summer. University of Illinois Extension notes that hollyhocks planted early in the season can be treated as annuals, which suggests early sowings sometimes flower the same year. See the timing page for details.

Care

Hollyhocks need little feeding. A slow-release fertilizer worked in at planting is enough, according to South Dakota State. The Wisconsin plant clinic adds that fertilizing beyond what a soil test calls for isn’t helpful.

Support: Stake tall stalks in windy or rich-soil sites, or tie them loosely to a fence. Sources differ here: NC State describes the spikes as rigid enough not to need staking, while Cornell, Texas Tech and Illinois all say staking may be needed, especially in wind. Illinois suggests pinching the main stem early in the season to get shorter, bushier plants that are less likely to need support.

Deadheading: Removing spent flowers right after bloom helps perennial types return, because the plant doesn’t spend its reserves on seed. Leave at least a few stalks to ripen if you want self-sown seedlings. Seed is ready when the pods are completely brown and dry.

Hollyhock rust

Rust is the most common hollyhock disease. It rarely kills plants outright, but it can stunt them and strip their leaves early. Look for orange to yellow spots, about 1/8 to 1/4 inch across, on the lower leaves. Brown to dark-red raised pustules form beneath them on the undersides. Badly infected leaves get holes, shrivel and drop. The fungus spreads on wind and splashing water and survives the winter in old hollyhock leaves and stems.

The Wisconsin plant clinic’s prevention steps:

1. Remove spotted leaves at the first sign of rust and put them in the trash or bury them deeply.
2. Clean up all hollyhock debris in fall.
3. Pull common mallow and other mallow-family weeds nearby, since they carry the same fungus.
4. Don’t save seed from infected plants, and check new plants for spots before you buy.
5. Space plants for air flow, and water with a soaker or drip hose instead of a sprinkler.

Rust-resistant varieties help, but they resist only some strains of the fungus, so don’t count on them alone. If you use a fungicide, choose one labeled for hollyhocks and apply it before symptoms appear, which is when it works best. South Dakota State notes that many gardeners eventually remove badly infected plants and replant in a new location.

Other pests and problems

NC State lists leaf spot and anthracnose as additional foliage diseases, and Japanese beetles, slugs, spider mites and hollyhock weevils as pests. Texas Tech adds root rot. NC State notes the leaves may wither in summer heat.

Regional notes

In West Texas, Texas Tech finds hollyhocks behave as biennials or weak perennials and will likely need staking against the wind. In the Arizona low desert, the University of Arizona chart has them planted in February-March or October-November, blooming April through June. Cornell lists hardiness as zones 3 to 9, and NC State as zones 5 to 9.

Varieties

Cornell describes the Powder Puffs strain (6 to 8 feet, dense double flowers), ‘Nigra’ (deep maroon, nearly black flowers on 5-foot plants), the Chater’s Double series and the 4-foot Summer Carnival series. NC State also features ‘Nigra’. Traditional hollyhocks have single flowers, and many newer cultivars are doubles.