UC Master Gardeners of Sonoma County
UC Master Gardener Program of Sonoma County

Spinach

Spinach can be one of the easiest crops to grow depending on the gardener’s choice of planting times. It is fast-growing, short-lived, heat-sensitive, and dependent on adequate fertility. By fortifying soil and avoiding high temperatures in summer, gardeners can enjoy several months of satisfying harvests.

Spinach Selections

  • Savoy spinach types have crisp, crinkly leaves and a firm texture.
  • Semi-savoy varieties are less crinkly and preferred by some for ease of cleaning.
  • Flat-leaf types have large, smooth, and more tender leaves than curly varieties.
  • Baby spinach involves harvesting immature leaves of any variety.
  • Some varieties perform differently when grown in spring or fall. Check seed packet and catalog descriptions for disease-resistant varieties, their tolerance of light frost and overwintering in mild microclimates, and any tendency to bolt, that is go to seed quickly, as spring warms up.
  • Malabar spinach is not a true spinach but shares the common name. It has leaves with a mucilaginous texture on a tropical perennial vine that grows in the warm season.
  • New Zealand spinach, of yet a different species, has fuzzy, succulent leaves, tolerates heat, and spreads in clumps. It also is not a true spinach.

Sowing and Growing

  • Amend seed bed with compost or aged manure for rich, fertile, well-drained soil.
  • Refrigerate seed one week before planting to encourage germination, particularly when planting in late summer.
  • Direct sow February-April after soil temperature reaches 50 degrees to grow during cool spring months with short days. Start seed indoors if soil is too cold or soggy from winter rains.
  • Plant again August-September as day length shortens for a fall crop. In a succession garden, some light shade from taller plants may be needed during late summer heat waves.
  • Sprinkle seed in beds over a 2-4 in. wide band, 12-15 seeds per row about ½ in. deep, and cover lightly with soil.
  • Thin to 3-4 in. apart or transplant starts when seedlings are 2 in. high. Snip thinnings at soil level to avoid disturbing roots of remaining seedlings.
  • Use loose, fast-draining potting mix at least 8 in. deep when planting in containers.
  • Repeat sowing every 2-3 weeks for a continuous harvest. Most varieties mature in 40-50 days.
  • Side dress spinach mid-season with compost, blood meal or kelp. Nitrogen-rich amendments encourage fast, tender growth.
  • Keep soil evenly moist with regular watering; spread mulch over beds to discourage weeds.

Harvesting

  • Harvest when leaves reach 4-6 in. long on plants that have developed at least 8 leaves.
  • Cut an entire plant at the base or break off outer leaves at the base of their stems in a cut-and-come-again method to allow for additional harvests.
  • Do not wait too long to harvest spinach or larger leaves will become bitter and plants may bolt.
  • Allow fall plantings to continue growing to maturity in cold weather that brings a moderate frost. Spinach can tolerate brief temperature drops to 20 degrees but benefits from a row cover in sustained lows. Growth may slow or stop before resuming when temperatures rise.  

Check for Pests

  • Check for pale-colored burrows inside thin leaves indicating leaf miners. Crush any eggs on leaf undersides and destroy severely damaged leaves.
  • Cover young seedlings with spun row covers to deter damage from birds.
  • Hand pick pests such as looper worms, slugs and snails; hose off aphids.
  • Expect fewer pests in a fall-winter garden.

Additional Information

February 2022