Planting
What to Plant in September
For half the map, the best planting month of the year. Bulbs, bare-root peonies, the fall perennial window, and one loud last call.
If August is the month the calendar argues with the heat, September is the month the calendar wins. Cooling soil that is still warm at depth is exactly what roots want, and nearly everything hardy wants planting somewhere on the map right now: spring bulbs in the cold half, peonies through the middle, and in zones 7 and 8 the opening of the best planting weeks of the whole year. Only the almost-frost-free south keeps waiting.
As always, the months here follow our planting calendar, which anchors every window to typical zone frost averages, and your garden is not an average: local frost dates swing by weeks either way, so read September as a season, not a deadline, and check your own zone's page for the fine print.
What should I plant in September?
By zone. In zones 3 and 4, finish the spring bulbs and stop there; in zones 5 and 6, this is the last month for perennials and shrubs, with bulb planting open alongside. In zones 7 and 8, September is the gateway: the year's best window for everything hardy opens now, peonies included. Wherever it is hardy, it is also the final month to plant or divide bearded iris. Frost dates vary by weeks, so check yours.
Spring bulbs: the window opens
The rule for the spring-flowering bulbs is 6 to 8 weeks before the ground freezes, and September is when that maths starts landing. Zones 3 and 4 are already finishing: September is their last month. Zones 5 and 6 open now and run through October. Zones 7 and 8 hold off until October and November, when their soil has actually cooled; bulbs planted into warm ground can sprout too early or sulk. If you have not ordered yet, our August guide covers the order-now logic; this month is about getting them into the ground.
Narcissus
The first bulb to plant, because it roots earliest: in the ground by late September in the cold zones. Deer never touch it, and one afternoon's planting keeps announcing spring, every March and April, long after you have forgotten the digging.
Tulipa
The most patient of the bulbs: it can go in any time before the ground freezes, so plant the daffodils first and the tulips after. April and May pay the invoice in almost every color there is.
Crocus
Cheap by the hundred and the earliest real color of spring, February and March. Tuck them anywhere: a drift under a tree, holes in the lawn, the front inch of a border.
Allium 'Globemaster'
The bulb for late spring: purple spheres in May and June on 2.6-foot stems, planted this fall like the rest. Deer and drought both leave it alone, and the seed heads stand all summer.
Peonies: this is the month
Peonies are planted in fall as bare roots, and September is the heart of it: zones 5 and 6 run August into September, zones 7 and 8 open now and run into October. In zones 3 and 4 the moment was late summer, so plant immediately or hold roots for spring pots. Set each root shallow, with the buds no more than about two inches down; planted deep, a peony grows happily and never flowers.
Paeonia
Set out as a bare root this month, anywhere in its zones 3 to 8 range, a peony often sulks through its first spring, offers a few flowers in its second, and then settles into decades of May and June shows. Buy it once, site it in full sun, and let it get on with a very long life.
Bearded iris: last call
Bearded iris plants and divides on its own clock, July to September, everywhere it is hardy, and this month closes it. If a clump has gone quiet in the middle or a neighbor is offering rhizomes, this is the week to act, not next month: divisions set out now still root before the cold. Replant each rhizome on the surface, top in the sun, and it flowers next May and June. The full how-to is in our dividing guide.
Perennials and shrubs: where September fits in your zone
The hardy fall window is the same deal everywhere, roots down in cool soil about six weeks before real frost, but September means a different thing at every latitude. The zone table is blunt about it.
| Zones | Typical first frost | What September means |
|---|---|---|
| Zones 3 to 4 | Mid to late September | Frost is here or close: the perennial window has closed, so finish the bulbs this month and call the planting year done. |
| Zones 5 to 6 | Early to late October | Last call for perennials and shrubs, with the window closing at the end of the month while bulb planting runs alongside. |
| Zones 7 to 8 | Early to late November | The gateway opens: September and October are the best planting weeks of the whole year for everything hardy. |
| Zones 9 to 10 | December, or rare to none | Still summer: hardy planting waits for October and November, when the cool season arrives to do spring's job. |
Whatever your zone, the aftercare is the same: a September planting spends its first weeks growing roots you cannot see, so soak it on day one and stay on the watering can until real rain arrives to relieve you. Steady moisture is the whole job.
Plant something blooming right now
The zones with an open window get one more treat: September is when the nurseries flip their benches to asters and mums, and anything hardy planted while in bloom settles in just as well while looking wonderful doing it.
Symphyotrichum oblongifolium 'October Skies'
A compact aromatic aster in true sky blue, flowering September and October at a tidy 1.6 feet. Planted in bloom, it feeds the last bees of the year in its first season and comes back stronger every fall.
Tricyrtis
The September surprise for shade: small sculpted flowers speckled like quail eggs, September into October, zones 4 to 8, in the same cool spots hostas love. Plant it beside a path, because the detail deserves a close look.
Chrysanthemum
Mum season proper: September is when garden centers stack them to the ceiling, and a well-budded plant keeps opening into October. Think of fall-bought pots as long-lasting decor rather than permanent residents; the mums that reliably return went into the ground back in spring.
Is September too late to plant perennials?
Depends entirely on your zone. In zones 3 and 4, honestly yes: frost is on the doorstep, so save the plant list for spring. In zones 5 and 6 you have until about the end of the month; in zones 7 and 8 you are not late, you are early, at the front of the best window of the year.
When exactly should bulbs go in?
About 6 to 8 weeks before your ground freezes: September in the cold half of the map, October and November in the mild half. Planting order helps too: daffodils first, because they root earliest, then the rest, with tulips last, since they are happy to wait.
Can I still divide bearded iris in September?
Yes, and it is the last month for it: the July to September window closes now. Lift, split, and replant with each rhizome sitting on the soil surface, and the divisions still root before winter. Our dividing guide walks through the whole job.
What about zones 9 and 10?
Hold on a few more weeks. September there is still summer by soil temperature; the hardy window opens in October and November, and the fall-planted bulbs follow in November and December. In the nearly frost-free garden, the cool season is the planting season.
Design a garden with these plants
Open BloomsEye Studio with this guide's plants ready to drop onto a plan, then watch the whole bed bloom across the year.