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When to Start Zinnia Seeds

Dates to start zinnias indoors, harden off and plant out for your ZIP code or zone.

Tomato and pepper seedlings in trays under an LED grow light

Zinnia planting dates by zone

At the average last frost date for each USDA half-zone (the median across its ZIP codes, NOAA 1991 to 2020 normals). Enter your ZIP code below for your own dates.

ZoneLast frostStart indoorsTransplantSow outdoors
3aMay 28Apr 30May 28May 28
3bMay 17Apr 19May 17May 17
4aMay 13Apr 15May 13May 13
4bMay 8Apr 10May 8May 8
5aMay 4Apr 6May 4May 4
5bMay 1Apr 3May 1May 1
6aApr 29Apr 1Apr 29Apr 29
6bApr 23Mar 26Apr 23Apr 23
7aApr 16Mar 19Apr 16Apr 16
7bApr 6Mar 9Apr 6Apr 6
8aMar 29Mar 1Mar 29Mar 29
8bMar 18Feb 18Mar 18Mar 18
9aMar 3Feb 3Mar 3Mar 3
9bFeb 2Jan 5Feb 2Feb 2
10aJan 16Dec 19Jan 16Jan 16
10brareby seasonby seasonby season
Your location

Zone medians. Your ZIP code gives the dates of your nearest weather station.

Frost risk

Half of years still get a frost after the spring date, and half get the first fall frost before the fall date.

Frost dates at three risk levels
AverageSaferSafest
Last spring frostApr 23Apr 30May 9
First fall frostOct 22Oct 16Oct 7
Crops (1 selected)

Start your first seeds indoors

Mar 26zinnia

Average frost dates: last Apr 23, first Oct 22 (zone 6b).
Season
Spring seed starting schedule
CropStart indoorsHarden offTransplantSow outdoorsNotes
ZinniaTenderMar 26Apr 2 to Apr 22Apr 23Apr 23Indoors 4 wk before last frost. Transplant at last frost. Sow outdoors at last frost. Sprouts in 3 to 5 days, best at 80 to 85°F soil. Pot up at the first true leaves.

How to start seeds indoors

Light
Give seedlings 14 to 18 hours of light a day on a timer, with fluorescent or LED fixtures 2 to 6 in above the leaves. Raise the lights as the plants grow.
Clemson HGIC: 16 to 18 hours, tubes 2 to 4 in above. UMD Extension: 14 to 16 hours, 2 to 6 in.
Seed starting mix
Use a sterile, soilless mix, never garden soil. To mix your own, combine equal parts by volume of fine pine bark, sphagnum peat moss and perlite.
NC State Extension Gardener Handbook; Clemson HGIC.
Sowing and warmth
Sow two or three seeds per cell and keep the strongest seedling. A mix temperature of 65 to 75°F germinates most vegetables; after they sprout, 55 to 60°F nights and 65 to 70°F days keep them stocky.
UMD Extension.
Potting up
Move seedlings into larger pots shortly after the first true leaves appear, while they are small and recover quickly.
UMD Extension; Clemson HGIC (one or two sets of true leaves).
Hardening off
Start two to three weeks before transplanting, once plants are about 3 in tall: set them outdoors by day, bring them in before sundown, and give them more direct sun each day. Skip days below 45°F or with strong wind.
Clemson HGIC: 2 to 3 weeks. NC State: at least 2 weeks, not below 45°F.

When to start zinnia seeds

Utah State University Extension starts zinnia seeds indoors 4 weeks before the last spring frost and plants them out once the frost has passed; the same date works for sowing directly in the garden, which NC State's plant toolbox recommends right after the last frost. Zinnias are frost sensitive, so neither the transplants nor the seed go out before that date.

ZoneAverage last frostStart indoorsHarden offTransplant or sow outdoors
5bMay 1Apr 3Apr 10 to Apr 30May 1
7aApr 16Mar 19Mar 26 to Apr 15Apr 16
9aMar 3Feb 3Feb 10 to Mar 2Mar 3

The frost dates are the median across each half-zone's ZIP codes (NOAA 1991 to 2020 normals), so in half of years a frost still comes later. The harden off window is the two to three weeks Clemson Extension recommends before transplanting, starting no earlier than the sowing date.

Indoors or direct?

Both methods share the same outdoor date, the last frost:

  • Started indoors, the plants are already about 4 weeks old when they go out. Utah State sows 1 to 2 seeds per cell.
  • Sown directly, they skip the indoor weeks and the hardening off. This is the method NC State's toolbox gives: sow seed directly in the ground after the last frost date.

Starting earlier than the table's indoor date only means older plants waiting indoors for the same frost-free day.

Warmth for germination

Zinnia seed likes it hot. Utah State gives an ideal soil temperature of 80 to 85 °F, and at that warmth seedlings appear in 3 to 5 days. That is well above normal room temperature, so indoor trays need a warm spot.

How far apart to plant them out

Set small types such as Zinderella, Queen and Mexican zinnias on a 9 by 9 inch grid and large cut-flower types such as Benary's Giant on 12 by 12 inches, per Utah State. The zinnia spacing calculator turns that into plants per bed or row, and so into how many cells to sow.

Using the planner

Enter your ZIP code above to use your own frost dates instead of the zone average, and switch the frost risk to Safer or Safest if you would rather not gamble on the first week. Add other flowers and vegetables to build a single sowing calendar, or open the seed starting calculator for the whole garden.