How to Grow Sweet William
Sweet William At a Glance
Difficulty
Moderate
Category
Flower
Sun Exposure
Full Sun, Partial Sun
Frost Tolerance
Frost Hardy
Cold Hardiness
Survives to -23°C
Plant Family
Caryophyllaceae
Growing Season
Cool Season
Plant Lifecycle
Biennial
How to Start It
★ Recommended for beginners
Sweet William flowers in its second year, so sow it in late spring or early summer for blooms the following summer. Sow seeds 0.5 cm deep in a spare corner or right where it will flower, and keep the soil damp: they sprout in 10 to 21 days. Thin them (pull the extras) so each plant has 20 cm, or move the young plants to their flowering spot by early fall so they settle in before winter.
Sweet William is a biennial: it makes a low clump of leaves the first year, survives the winter, then flowers heavily the next summer. Let a few flower heads drop their seed and new plants will keep coming up on their own, so you get flowers every year.
When To Start
First chance to plant
30 Days Before Last Frost
Last chance to plant
60 Days Before First Frost
When should you plant Sweet William?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Sweet William Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Sweet William Calendar
Set your location to turn these into exact dates and reminders.
Sow sweet William now for flowers next summer
60 days after your last frost· every year
Cut sweet William for the vase and snip off faded flowers
320 days after your last frost· every year· optional
Did you water your sweet william seedlings today? Keep the top of the soil damp until they are up and growing.
About 1 days after you plant it
Time to thin the sweet william seedlings: snip the extras at soil level so each one has room to grow.
About 31 days after you plant it
How is your sweet William doing? Keep the soil lightly moist while the seedlings grow.
About 30 days after you plant it
Checking in on your sweet William. This year it builds a leafy base, and the flowers come next year.
About 90 days after you plant it
Picking time may be here: check your sweet william.
About 90 days after you plant it
The Journey Ahead
Sweet William's Lifecycle
Seedling
Mature Plant
Seed Production
Step 2
Planting & Sprouting
Expect sprouts in 10–21 days
Growing Tips
- 1Plant sweet William in full sun, or a spot with afternoon shade where summers are hot.
- 2Give it well-drained soil with a little compost, since it rots in soggy ground over winter.
- 3Water when the top few cm of soil are dry, and keep the soil evenly moist while the seedlings are young.
- 4A light feed of compost tea in spring, as the flower stems grow, is all it needs.
- 5Wash aphids off with a spray of water and pick slugs off at dusk.
- 6Keep pets from chewing it, as it can upset a cat's or dog's stomach.
Seedling Phase
Step 3
Growth & Maturity
~90
Days to Maturity
45 cm
Mature Height
30 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
Harvest Window
30 days
When to Pick
Harvest flowers at peak color
How to Harvest
- 1Cut stems for a vase when about a third of the small flowers in each cluster have opened.
- 2Cut early in the morning and put the stems straight into water.
- 3Snip each stem just above a pair of leaves, which can give you a smaller second round of flowers.
- 4Cut off faded clusters to keep the plant tidy, but leave a few to make seed if you want new plants.
Step 5
Saving Seeds
How to Save Seeds
Sweet William only makes seed in its second year, after it flowers. It can cross with pinks and carnations flowering nearby, and hybrid F1 types will not come true, so expect some new colours. Leave a few faded flower clusters on the plant until the small pods turn brown and dry and the tips start to open. Snip them into a paper bag, shake out the small black seeds, and let them dry a few more days. Store them labelled somewhere cool, dark and dry, where they keep about 3 to 4 years.
Seed Production
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