Growing Sweet Alyssum: A Complete Profile
By Growing Home Greens Team · July 18, 2026
Sweet alyssum is one of the better-documented companion flowers in this whole list, backed by actual published field research on why it’s planted alongside crops like lettuce and broccoli. It stays low, a 4- to 8-inch spreading mat, and disappears under dense clusters of tiny, four-petaled white or purple flowers.
Surface-sown seed that needs light
Sweet alyssum can be started indoors about 7 weeks before your last frost or direct-sown right around that date; either way, the seed needs light and shouldn’t be covered. It’s fast, reaching maturity in about 40 days, and dense (3 plants per square foot) since its job is to form a low, spreading mat rather than stand as an individual plant. Use it as a living mulch or border between rows rather than planning dedicated bed space around it.
A midsummer slowdown that a hard trim fixes
Sparse, leggy growth usually means too much shade or too little water. Sweet alyssum wants consistent moisture and will stall out in a dry spell. A midsummer slowdown in bloom is common in hot climates; shearing plants back by about a third often triggers a fresh flush once temperatures ease, especially with heat-tolerant varieties.
A hoverfly draw with the research to back it
A published field study found sweet alyssum intercropping attracts hoverflies that reduce aphid pressure on nearby brassicas, and it’s used commercially as an intercrop with lettuce for the same reason. See the full companion guide for sweet alyssum. Its low, spreading habit makes it a natural border or living-mulch choice in the Garden Designer, tucked along the edges of the beds it’s protecting rather than occupying prime square footage.
Companion planting guide for Sweet Alyssum · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Mature height: 3-10 in
Method: Either: Start indoors for an earlier harvest, or direct-sow outside for less fuss. Either works.
When to plant sweet alyssum, by zone
Every zone sweet alyssum grows in. Pick your zone in the header and it will be highlighted here. Each zone links to its full page.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 2a & 2b | Apr 1–Apr 8 | May 20–May 27 | Jun 29–Jul 6 |
| 3a & 3b | Apr 11–Apr 18 | May 30–Jun 6 | Jul 9–Jul 16 |
| 4a & 4b | Mar 27–Apr 3 | May 15–May 22 | Jun 24–Jul 1 |
| 5a & 5b | Mar 22–Mar 29 | May 10–May 17 | Jun 19–Jun 26 |
| 6a & 6b | Mar 7–Mar 14 | Apr 25–May 2 | Jun 4–Jun 11 |
| 7a & 7b | Feb 20–Feb 27 | Apr 10–Apr 17 | May 20–May 27 |
| 8a & 8b | Feb 4–Feb 11 | Mar 25–Apr 1 | May 4–May 11 |
| 9a & 9b | Dec 28–Jan 4 | Feb 15–Feb 22 | Mar 27–Apr 3 |
| 10a & 10bFall window | Aug–Jan | Oct–Mar | ~40 days after transplanting |
| 11a & 11b | Nov 13–Nov 20 | Jan 1–Jan 8 | Feb 10–Feb 17 |
Bloom dates are about 40 days after the sow or plant-out date, not after starting seeds indoors.
Zone 2 sows before zone 3 here, which looks wrong and is not. USDA zones rank winter cold, not season length, and zone 2 is mostly interior Alaska, where hard winters come with warm summers. More on what a zone measures.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Sweet Alyssum plants fit per square foot?
Spacing: 3 per square foot (square-foot-gardening spacing). Mature height: 3-10 in.
Good companions for sweet alyssum
- Broccoli: Sweet alyssum intercropping is documented to attract aphid-eating hoverflies, but the published research behind this (Brennan 2013) specifically tested lettuce, not broccoli: treat the broccoli extension as plausible but unconfirmed by that study.
- Lettuce: A published field study (Brennan 2013, Biological Control) found strip-intercropping lettuce with sweet alyssum reduces aphid pressure via hoverflies, whose larvae can eat up to 150 aphids a day: real, measured pest control, not folklore.
Full companion guide, including what to keep away from sweet alyssum →
Varieties worth considering
- 'Snow Crystals': University of Wisconsin-Madison Extension describes this tetraploid variety as vigorous with a mounding habit, large white flowers, and improved heat tolerance over standard sweet alyssum, useful if your bloom window needs to stretch through a hot summer to keep attracting hoverflies. (source) Buy seeds: True Leaf Market
- 'Easter Bonnet' series: An early-blooming series Wisconsin Extension lists in Deep Pink, Deep Rose and Violet, at 4-10 inches tall. The pick if you want color beyond Snow Crystals' white without giving up an early bloom start. (source) Buy seeds: True Leaf Market
- 'New Carpet of Snow': A compact white type Wisconsin Extension lists at just 3-4 inches tall, lower and tighter than Snow Crystals. Good for a true low mat right at a bed's edge rather than a fuller mounding border. (source)
Why each variety is listed comes from the source shown next to it. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement. The buy links are separate from those sources: they go to seed suppliers that sell that exact variety, and we may earn a commission on some of them.
Where to buy sweet alyssum seeds
High Mowing Organic Seeds (sweet alyssum seeds)
The varieties we recommend above each have their own buy links, for the suppliers that sell that exact variety.
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See it growing
Search YouTube for "growing sweet alyssum" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Sweet Alyssum: A low, spreading groundcover flower with field-study backing for pulling aphid-eating hoverflies into vegetable beds.
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