Spinach is a fast-growing, cool-weather loving green that you can plant in spring and fall. Summertime heat makes the leaves tough and bitter and causes the plants to bolt, so keeping to planting in cool weather ensures sweet, tender harvests.
Ideal growing temperatures are between 35-75° though will not readily germinate in temps above or below 50°.
Choose a spot in your garden that gets full sun, at least 6 hours a day to plant your seeds or transplants. Though spinach will do alright in part-shade, they plants will not be a vigorous or productive.
Spinach will do best in well-drained soil with a couple inches of compost worked in.
Decide when to plant your spinach depends on your first and last frost date. For a spring harvest, plant your spinach 4-6 weeks before the last spring frost. This first, early crop will bolt, so harvest before you reach 14 hours of sunlight a day for best results. For fall harvest: plant 6-8 weeks before the first fall frost for a more reliable fall crop. You can also overwinter a fall planting if you plant spinach in autumn and allow the crop to go dormant over the winter and harvest in the spring as it picks back up in growth as the days start to lengthen.
Sow seeds ½" deep and two inches apart. Make sure the rows are spaced at least 8” apart if planting in rows. Doing so allows the seeds to mature without having to compete for space. Pat seeds in so they have good contact with the soil and water well. Keep moist while you wait for germination, which can be sporadic but happen within 21 days. If you are transplanting seedlings, space spinach plants about 12-18” apart. This allows the seedlings to grow and expand their roots without competing with each other for space.
Mulch your plantings with a couple inches of your favorite organic mulch to help keep weeds at bay. Hand pull weeds that do emerge, but do so carefully as spinach has shallow roots that are easily disturbed.
As your spinach plants grow into seedlings, thin them lightly to prevent the plants from competing for space. You want the plants to be spaced far enough apart that the leaves of neighboring plants barely touch, if at all. Remove plants several times during growth to keep this balance, saving the tender young leaves for eating.
If your spinach plants are growing slowly, you may want to add more nitrogen-based fertilizer. As mentioned above, spinach likes soil rich in organic matter such as well-rotted manure, alfalfa meal, soybean meal, cottonseed meal, and blood meal. Add the fertilizer according to label recommendations and water thoroughly.
As soon as the leaves grow big enough to eat (usually about three or four inches in length and two or three inches wide), you can harvest your spinach leaves. It generally takes about six to eight weeks from planting to harvest. Harvest the spinach by carefully removing the outer leaves. Either pinch at the base of the petiole with your fingers or use gardening shears to snip the base of the petiole.