Like all vegetables, spinach (Spinacia oleracea) plants grow not to feed people but to produce the seeds that will ensure their species' survival. You'll know your spinach plants are at the seed-producing stage when a tall, flower-bearing stem suddenly shoots up. This natural process, called bolting, occurs with increasing daylight hours and temperatures. The changing conditions signal the plants to divert energy from edible leaf production to seed production. Bolting makes spinach plants tough, bitter and ready for the compost heap.
Study spinach seed varieties for heat resistance before making a purchase. Some hybrid varieties, including Spinner and Correnta, produce through the summer without bolting. They may be labeled "long-standing" or "slow to bolt." Hybrids marketed as cool-season or broadleaf varieties, however, suffer at temperatures above 75 degrees F.
Plant your spinach at the right time. Sow cool-season variety seeds one month to six weeks before the final spring frost date. Follow them with heat-resistant varieties planted from late spring into midsummer. For a late-season crop, resume sowing cool-season seeds two months to six weeks before your earliest autumn frost date. Planting at two-week intervals ensures a spring-to-fall supply of fresh spinach.
Water your spinach with the hose frequently enough to keep the soil moist until the seedlings appear. Continue watering at the rate of 1 inch every week to 10 days during dry periods. Dry soil increases the likelihood of bolting.
Harvest the outer leaves from your spinach rosettes as soon as they're big enough to eat. Let the inner leaves keep growing. Harvesting in stages, instead of pulling up the entire plant, delays bolting.
Remove new stalks from your spinach plants with stem clippers as soon as they emerge. This process is the same as removing the spent blooms from your ornamental annuals. The longer you delay seed production, the more spinach leaves you'll harvest.
Things You Will Need
- Garden hose
- Stem clippers
- Plant your spinach in organically rich, sandy loam with a pH reading between 6.4 and 6.8. Excessively acidic soil discourages seed germination and yields slowly growing seedlings. The heaviest harvests of edible leaves come from plants in their preferred soil.
- Spinach plants remaining in the garden after bolting will self-sow. Some of the seeds they drop germinate into a volunteer crop after soil temperature drops in the fall.
- After removing non-producing spinach plants from the garden, clip off the seed heads with the stem clippers before composting them. Intact seed heads may result in spinach plants cropping up wherever you use the compost.