Before moving your spinach seedlings outside, you will need to let them 'harden off' for two weeks to acclimate to your area. Set them outdoors in a protected porch with bright, indirect light away from the wind. Set them out four weeks before the last spring frost in your planting zone. Continue to keep the seedlings moist but not soggy. Never let them dry out. Gradually move them to more exposure after the second week. If a hard freeze is predicted, bring them indoors for protection. After the two-week acclimation is over, dig planting holes the same size, width, and height as the grower pot. Next, add some rooting hormone at the base and place your seedling out of the grower pot into the hole and water. Then backfill the holes with native soil mixed with compost or amendments. Be careful not to bury the stems deeper than previously planted in the grower pots, as this can rot the plant. Finally, plant your spinach seedlings a foot apart to allow growth and air circulation.