Annual Flower

When to Plant Zinnias in New Hampshire

The cut-and-come-again champion. The more you cut zinnias, the more they bloom. A cottage garden essential.

The Short Answer

In New Hampshire, plant zinnias based on your regional frost dates. Northern New Hampshire has a last frost around May 20 - Jun 5, while Southern New Hampshire sees frost end around May 1 - May 20. Short growing season especially in north. Cold winters. Cool summers. Hardy varieties important.

New Hampshire Frost Dates

Your planting dates depend on which part of New Hampshire you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Northern New Hampshire 3b, 4a, 4b May 20 - Jun 5 Sep 10 - Sep 25
Southern New Hampshire 5a, 5b, 6a May 1 - May 20 Sep 25 - Oct 10

Zinnias Planting Schedule for New Hampshire

Northern New Hampshire (Zones 3b, 4a, 4b)

Average last frost: May 20 - Jun 5 · Average first frost: Sep 10 - Sep 25

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Southern New Hampshire (Zones 5a, 5b, 6a)

Average last frost: May 1 - May 20 · Average first frost: Sep 25 - Oct 10

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Growing Zinnias in New Hampshire

Zinnias in New Hampshire's Climate

Zinnias are one of the best annual cut flowers for cold climates — they grow fast enough to bloom for months even in short seasons. Direct sow after your last frost when soil reaches 60°F. The more you cut, the more they bloom, producing armloads of color from July through first hard frost.

Soil Considerations for New Hampshire

Rocky, acidic New England soils. Glacial deposits. Granite bedrock. Raised beds essential in many areas. Make sure soil has warmed to at least 60°F before planting zinnias outside.

New Hampshire Climate & Growing Season

Short growing season especially in north. Cold winters. Cool summers. Hardy varieties important. Zinnias cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.

Growing season length varies across New Hampshire: Northern New Hampshire (3b, 4a, 4b) has a last frost around May 20 - Jun 5, while Southern New Hampshire (5a, 5b, 6a) sees frost end around May 1 - May 20. This difference matters for zinnias — transplant timing shifts by several weeks across the state.

Growing Tips

Water at the base to prevent powdery mildew. Cut flowers just above a leaf node to encourage more branching and blooms.

Companion Planting

Plant zinnias alongside these companions for better growth:

Tomatoes Peppers

The Bottom Line

Zinnias can be grown successfully across New Hampshire, but your exact planting dates depend on which region you're in. Northern New Hampshire gardeners should plan around a May 20 - Jun 5 last frost, while those in Southern New Hampshire can typically plant earlier. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Zinnias Growing Guide National planting guide with all states New Hampshire Planting Calendar All plants for New Hampshire Zinnias in Alabama Alabama planting dates Zinnias in Alaska Alaska planting dates Zinnias in Arizona Arizona planting dates Zinnias in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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