Snapdragons: A Complete Guide to Sowing, Growing, and Caring

Snapdragons (Anthirrhinum majus) are a delight, with their showy, butterfly-attracting flowers and their low-maintenance requirements. Most are grown as annuals since they tend to die back after heavy frost, but they can also be grown as short-lived perennials in warmer areas. They can also self-seed.

Basic Information

Height at maturity: 25-150 cm (depending on the variety)
Width at maturity: 20-40 cm (depending on the variety)
Light needs: Full sun to partial shade
Hardiness: Down to 0 degrees C
Type of soil: Well draining
Soil pH: neutral to alkaline
Pests and disease: Sensitive to spider mites, thrips, aphids and whitefly
Diseases: Botrytis blight, Rhizoctonia, Rust, Pythium, Powdery and
Downy mildew
Where to plant: Pots, flowerbeds, rock gardens and borders
Features: Fragrant; great for biodiversity and pollinators - attracts hummingbirds and butterflies
Pruning: Pinch off any dead foliage; remove old flowers to encourage new blooms
Flowering period: May-October
Best time to sow seeds: March-April, September-October
Pet safe

Starting your Seeds

You can either direct seed your snapdragon seeds in the fall, later spring, or early summer, or you can sow them in a greenhouse in seed cells 8-10 weeks before planting out.

Cover your seeds with a thin layer of vermiculite to retain moisture and hold seeds in place. Bottom water or mist lightly to avoid moving the seeds for 3-5 weeks at 13-18°C (55-65°F) in full light are ideal conditions for seedling development. Keep the soil mixture moist all throughout this stage.

Time to germinate: 10-14 days
Ideal germination temperature: 17-21°C (65-72°F)
Plant spacing: 30-60 cm (12-24 in)

Soil reccomendations

Beds in locations with naturally sandy loam soils may be suitable for growing snapdragons without any amendments.

Heavy soils should be improved prior to planting by tilling in organic material such as peat moss, rice hulls, compost, or decomposed manure.

Growing medium for raised benches should consist of less than 50 percent field soil, with the remaining percentage consisting of a mixture of more than one of the following: vermiculite, perlite, peat moss, composted bark, or rice hulls.

If using compost, make sure it is free of disease-causing organisms. It may be necessary to disinfect the soil.

Young plants

After 3-5 weeks, you can start hardening off snapdragon seedlings and transplanting them outdoors. They can now be exposed to temperatures as low as 18ºC (64ºF).

Reduce soil moisture levels to obtain optimum root penetration and to prevent fungal diseases. Allow soil mixture to dry between waterings.Ideally, you should water in the morning. Keep leaves dry especially after nightfall.

A broad spectrum fungicide may be applied to prevent damping off. Extending day length to 14 hours will promote early flowering.

Growing on

After 5-6 weeks like this, they will be able to withstand temperatures as low as 16-18ºC (60-64ºF). Anything lower will increase the risk for poor growth and leaf chlorosis.

By this time, after the second true leaves unfold, you can transplant them. Leave in the greenhouse for the first 24 hours after transplanting. It will take another 5-6 weeks to adjust to new pots.

Continue allowing soil mix to dry between watering but do not allow plants to wilt severely as this will damage their growth.

Harvest when pollen is visible on the flowers and there are at least 5-7 open florets. Hang to dry.

Advice

Antirrhinum is very susceptible to high salt levels in all stages. The root system is also very sensitive. Prevent over watering and cold media (less than 15ºC/58ºF). Do not allow plants to wilt severely. It's best to water your plants in the morning.

Using support nets might be reccomended on tall varieties to keep them upright, but not necessary.

You can use labelled fungicides to prevent and/or cure problems. Do not use ammonium-based fertilizers as this will result in thin, elongated roots more susceptible to soil born fungi. Avoid overhead watering; allow foliage to dry during daytime to prevent disease.