🍃When to Plant Spinach in USDA Zone 4a (2026 Guide)
Very cold-hardy. One of the first things you can sow in spring. Here is the cool-season planting schedule for spinach in zone 4a (covering areas like northern Wisconsin, Fargo ND). All dates are based on 2026 frost data for your zone.
Direct sow
Apr 5
Harvest From
May 15
Because spinach is a cool-season crop, it tolerates light frost and can go out around Apr 5, before zone 4a's average last frost on May 10.
- Type: Cool-season
- Method: Direct sow
- Days to harvest: 40
- Spacing: 4" apart
- Sun: Full sun to part shade
- Zone 4a frost: May 10 – Sep 25
- Season length: ~138 days
- Companions: radish, strawberry, peas
Growing spinach in zone 4a
Zone 4a has an average last spring frost around May 10 and a first fall frost around Sep 25, giving roughly 138 frost-free growing days. That window comfortably fits spinach's 40-day cycle, with room for a second succession planting if you time it right.
Spinach resents transplanting, so direct sow it right in the garden around Apr 5. Give each plant about 4 inches of space in full sun to part shade.
Zone 4a specific growing notes
In zone 4a (northern Wisconsin, Fargo ND), your 138-day growing season means spinach should be one of your first spring plantings. Cool-season crops thrive in the mild part of your growing window. Monitor soil temperature — spinach germinates best when soil is 40-75°F.
Your first fall frost around Sep 25 means your last possible harvest is roughly late Sep. For a continuous supply, consider succession planting every 2-3 weeks from Apr 5 through mid-season.
Pro tip for spinach
Soak seeds in water for 12-24 hours before sowing to soften the tough seed coat and speed germination, especially when soil is still cool. Spinach germinates best in soil between 40-70°F.
Troubleshooting spinach
Leaf miners tunnel inside leaves creating winding translucent trails. Remove and destroy affected leaves immediately—do not compost. Row cover at planting prevents the adult fly from laying eggs.
Growing spinach in containers
Shallow 6-inch deep containers are plenty—spinach has a modest root system. Great for windowsill growing indoors year-round. One 12-inch pot provides enough for weekly salads.
Can you plant spinach twice a year?
Yes—sow in late summer (August in zones 5+, September in zones 7+) for a fall and early winter harvest. Spinach thrives in cooling weather and can survive temperatures down to 15-20°F.
Frequently asked questions
When should I plant spinach in zone 4a?
Direct sow around Apr 5. Because spinach is a cool-season crop, it tolerates light frost and can go out around Apr 5, before zone 4a's average last frost on May 10.
How long does spinach take to grow in zone 4a?
About 40 days from sowing to first harvest. A Apr 5 planting in zone 4a is typically ready to pick from around May 15. Zone 4a has about 138 frost-free days — plenty of time for a second succession planting.
How far apart should I space spinach?
Space spinach about 4 inches apart in full sun to part shade. This gives each plant enough room for roots to spread and leaves to catch sunlight without competing.
What is the best tip for growing spinach?
Soak seeds in water for 12-24 hours before sowing to soften the tough seed coat and speed germination, especially when soil is still cool. Spinach germinates best in soil between 40-70°F.
What are common problems with spinach and how do I fix them?
Leaf miners tunnel inside leaves creating winding translucent trails. Remove and destroy affected leaves immediately—do not compost. Row cover at planting prevents the adult fly from laying eggs.
Can I grow spinach in a container?
Shallow 6-inch deep containers are plenty—spinach has a modest root system. Great for windowsill growing indoors year-round. One 12-inch pot provides enough for weekly salads.
Can I plant a second crop of spinach for fall harvest?
Yes—sow in late summer (August in zones 5+, September in zones 7+) for a fall and early winter harvest. Spinach thrives in cooling weather and can survive temperatures down to 15-20°F.
What grows well next to spinach?
Good companion plants for spinach are radish, strawberry, peas. Avoid planting near warm-season crops that compete for space and nutrients. Spinach also benefits from crop rotation — do not plant it in the same spot year after year.