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Zinnia seeding indoors - timing for outdoors #924200

Asked February 03, 2026, 4:57 PM EST

Hi - I am in Hood River (HR) and had an unusal set of failure with seeds last spring due to so very little April rain (and my absence). This year I plan to start zinnia seeds indoors and I have watched several videos on prepping the seeds, but am trying to work out the timing. I want the zinnias robust in blooms in mid-late July (not all varieties but this is not unusual when I seed outdoors). Questions are: 1) Is a south window sufficient to set the seedling trays or should I use grow lights? 2) When should I start the indoor seeds? 3) How long can the germinated seeds remain in their small seed trays before moving outdoors? and 4) When would be a reasonable time to move them into the garden as seedlings based on my late July goal? Ok to respond with references to 'last frost' etc. but approximate dates in normal HR would be helpful. Much appreciated!

Hood River County Oregon

Expert Response

Hi Cathy,

I apologize for the delayed response! I will include some basic information in this email, but if you have already started your seeds or have further questions, please feel free to reach out to me directly through the email and phone # in my signature line.

Zinnias are a sun-loving annual, and seedlings do best under grow lights placed 2-3 inches from the plants. If you don't have a grow light, place the trays in uncoated south-facing windows that get full sun. Seedlings will need to be rotated to prevent leggy growth. 

Flowers typically bloom 8-12 weeks after planting, depending on the variety. This will be noted on your packages. If your goal is mid-July, you would plant your seeds in mid-late April. You will most likely want to transplant seedlings to a larger pot a few weeks after planting, as zinnias grow quickly and can become root-bound and stunted. Be sure not to disturb the roots when you up-pot the plants.

Hood River's average last frost date is around May 5, but this varies greatly depending on elevations throughout the county. If you live closer to Parkdale, frost is still common through the end of May. As you've likely seen, this year we seem to be around 8-15 days ahead of schedule, but we could still have a late frost. As zinnias need temperatures consistently over 70 degrees, including soil temperature, it would be best to monitor these temps and plan to plant accordingly. Typically, this would be around the second week of June, though last year our temperatures dipped into the 50s until July!

Please reach out if you have other questions. You can also learn more about zinnia care through excellent publications from Clemson Cooperative Extension and University of Minnesota Extension.
Best,


Megan Wickersham
Outreach Program Coordinator
Hood River County Extension
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An Ask Extension Expert Replied February 25, 2026, 6:14 PM EST
Great timing and most welcome. Thanks for the help!
On Wed, Feb 25, 2026 at 3:15 PM Ask Extension <<personal data hidden>> wrote:
The Question Asker Replied February 25, 2026, 6:30 PM EST

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