Prepare the bed: loosen the soil and mix in an inch or two of compost.
Plant seeds on your city's dates, ¼ inch deep, 9 to 12 inches apart.
Keep the soil evenly moist until sprouts appear, which can take one to three weeks in cool soil.
Harvest: Cut when stems are stiff right below the flower (give it a gentle wiggle test). Cut long stems often; the more you cut, the more they bloom.
Key numbers
70–80°FSoil to sprout
5.5–7.5Soil pH
60–75Days to bloom
Powdery mildewBiggest risk
Growing notes
What makes the difference in Northwest gardens, in plain language.
Wait for warm weather
Zinnias come from hot, dry regions and do nothing in cold soil. Seeds sown too early west of the Cascades often rot, and seedlings sit stunted and yellow. Sow once the soil is warm and nights are mild, usually late May to early June on the west side. They catch up fast: a sowing in early June often blooms by midsummer.
You can start them indoors a few weeks early, but transplant them young, since older seedlings don't like root disturbance.
Pinching and cutting
When a young plant is about a foot tall with three or four pairs of leaves, pinch out the top just above a leaf pair. The plant branches, and those branches give more stems and longer ones for cutting.
Cut flowers often and cut deep, down to a leaf pair low on the stem, so new branches have room to grow. Check for ripeness with the wiggle test: a stem that stays stiff just below the flower will last in the vase, while a floppy one wilts quickly.
Mildew, and east vs west
Powdery mildew coats leaves with white powder in late summer, when warm days and cool, damp nights alternate, a typical west-side pattern. Space plants for airflow, water the soil instead of the leaves and choose resistant varieties like Zahara. It looks bad but rarely stops flowering.
East of the Cascades, zinnias thrive in the heat and mildew is less of a problem, though steady water keeps them blooming. Slugs on young seedlings are the bigger west-side issue.
Common questions about growing zinnias
Should I pinch my zinnias?
Yes, for cut flowers. Pinch the top when plants are about a foot tall; they'll branch and give many more long stems. Skip pinching on dwarf bedding types.
What is the white powder on my zinnia leaves?
Powdery mildew, a fungus common in late summer. Remove the worst leaves, water at the base and give plants more room. Next year, try resistant varieties like Zahara.
Why don't my zinnias last in a vase?
They were likely cut too early. Use the wiggle test, cut in the cool of the morning, strip the lower leaves and change the water often. Zinnias prefer clean water without much floral preservative.
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