Spinach is a leafy green valued for its nutritional content and is almost always grown from seed. Starting with seed offers the most control over variety selection and planting time, allowing gardeners to maximize their harvest windows. Successful propagation relies on understanding the plant’s needs and following specific steps from sowing to transplanting.
Understanding Optimal Growing Conditions
Spinach is a cool-season crop, thriving in mild temperatures between 50°F and 70°F (10°C and 21°C). Temperatures above 75°F (24°C) cause the plant to “bolt,” sending up a seed stalk that makes the leaves bitter.
This dictates two main planting windows: early spring and late summer for a fall harvest. Seeds can be directly sown outdoors as soon as the soil temperature is above 40°F (4°C), typically four to eight weeks before the last expected spring frost. For a continuous supply, sow additional seeds every 7 to 10 days during the cool season.
Spinach requires fertile, well-draining soil rich in organic matter, with a preferred pH between 6.5 and 7.5. Amending the bed with compost or aged manure before planting is beneficial.
Step-by-Step Seed Starting
Seeds should be placed about one-half inch deep into the prepared soil for necessary darkness and moisture retention. For direct sowing, place seeds two to four inches apart in rows spaced 12 to 18 inches apart. Planting closer initially ensures a full stand and allows for later thinning.
If starting indoors, use a quality seed-starting mix in trays or small pots, ensuring only one seed per cell to minimize root disturbance. Avoid using heat mats, as the warmth can inhibit spinach germination.
Keep the soil consistently moist but never waterlogged, which can lead to fungal issues. Use a fine mist sprayer or gentle watering can to prevent dislodging the seeds. Optimal soil temperatures for germination are between 45°F and 68°F (7°C and 20°C), with emergence typically occurring within 7 to 10 days.
Once indoor seedlings emerge, ensure they receive ample light from a sunny window or a dedicated grow light. This prevents them from becoming thin and elongated, a condition known as legginess.
Thinning, Hardening Off, and Transplanting
Once spinach seedlings develop their first set of true leaves, it is time to thin the crop. Thinning removes excess plants to reduce competition, ensuring the remaining plants mature. Aim for a final spacing of six to twelve inches between each plant.
The best method for thinning is to snip the unwanted seedlings at the soil line using small scissors. Pulling them out can disturb the roots of the remaining plants. The removed young greens are edible as baby spinach.
Hardening Off
Seedlings started indoors need a gradual transition to the outdoor environment, known as hardening off, before transplanting. This process builds tolerance to wind, direct sunlight, and temperature fluctuations. Over seven to ten days, slowly expose the plants to outdoor conditions, starting with one or two hours of shaded time and incrementally increasing the duration and intensity of sunlight.
Transplanting
When transplanting, handle seedlings with care to avoid damaging the taproot. Dig a hole slightly larger than the root ball and plant the seedling at the same depth it was growing in the container. Water the transplants immediately to help settle the soil and reduce transplant shock.