Planting Calendar Johnston, IA

Frequently Asked Questions

How Accurate Are the Planting Dates?

Use this chart as a planning guide and starting point. The frost dates are averages based on historical data—they are not predictions for the coming year. While most gardeners rely on frost dates to plan planting, some locations in the U.S. may not experience frost, and certain areas may not match these dates perfectly.

Local microclimates—such as low spots, slopes, or sheltered areas—can also affect your planting schedule. Watch the weather, talk with fellow gardeners, and take notes on what works best in your garden.

Why Do You Start Seeds Indoors?

Starting seeds indoors gives crops a head start on the growing season, which is crucial in regions with shorter seasons. Indoors, young plants grow in a stable, controlled environment, protected from unpredictable rain, drought, frost, temperature swings, pests, and diseases.

For most crops, seeds should be started 6–8 weeks before the last spring frost. This ensures plants grow large and healthy enough to survive transplanting outdoors. Read more about starting seeds indoors here. Read more about starting seeds indoors here. 

Which Seeds Should Be Started Indoors?

Not all vegetables benefit from indoor starting. Most are better off direct-sown in the garden.

• Seeds that should be started indoors are typically:
• Tender vegetables: tomatoes, peppers, eggplant
• Long-season crops: broccoli, cauliflower, Brussels sprouts

Crops like carrots, radishes, beets, squash, and watermelon are best sown directly in the garden, as they do not tolerate root disturbance and need warm soil to thrive. Read more about direct-sowing seeds here!

When Should You Transplant Seedlings?

Transplant seedlings when they outgrow their trays or starter pots.

• If outdoor conditions aren’t ready, move seedlings to larger pots indoors.
• Begin hardening off approximately one week before the last frost date to gradually acclimate plants to outdoor conditions.
• Then transplant them into the garden. Get more tips for transplanting seedlings.

What Is Planting by the Moon?

Planting by the Moon (or “Gardening by the Moon”) is a traditional method for timing crop planting based on lunar phases:

• Above-ground crops: Plant annual flowers and vegetables during the waxing Moon (new to full).
• Below-ground crops: Plant bulbs, biennials, perennials, and root vegetables during the waning Moon (full to new).

Gardeners report larger, tastier harvests using this method. Our planting calendar includes Moon dates to help you plan. Learn more about Planting and Gardening by the Moon.