How to Grow Spinach Indoors (Without It Bolting or Refusing to Germinate)

Spinach shows up on every “easy indoor greens” list next to lettuce, and it isn’t quite fair to either crop. Lettuce mostly just wants light. Spinach wants light and cool conditions, and it punishes you differently for getting it wrong — instead of stretching and going pale, it either refuses to germinate at all or bolts to seed within a few weeks of looking fine. Both outcomes are avoidable once you know spinach is running on a different set of rules.

Why spinach is trickier than lettuce indoors

Two things make spinach the more demanding of the two.

Germination needs cold, not warmth. Most seeds germinate faster as temperature rises. Spinach is the opposite past a point — germination slows sharply above about 70°F (21°C) and can stall out closer to 75°F (24°C). A centrally heated flat in winter, ironically the season spinach prefers, can be too warm for the seed tray even when the room feels perfectly mild.

It’s a long-day plant, and that’s a problem you create yourself with a grow light. Spinach bolts (runs to seed) once day length gets long enough, generally somewhere past 14 hours — a trigger built into the plant to make it flower before summer heat arrives. Outdoors that’s a seasonal signal. Indoors, running a grow light 16 hours a day because “more light is better” recreates high summer artificially and can send a healthy-looking tray to seed in a few weeks. With spinach, more hours of light is not automatically better.

Setup

• A tray or wide pot, 15–20 cm (6–8 in) deep with drainage holes. Wide matters more than deep — spinach roots are shallow, similar to cut-and-come-again lettuce.
• Ordinary multi-purpose compost, levelled and firmed lightly.
• The coolest bright spot you have. An east-facing sill, a north window, or a spot back from a south window all work better than a hot glasshouse- style bay. Spinach is one of the few crops here that prefers less heat than a sunny windowsill often provides.

Sowing and germination

Sow seed about 1–2 cm deep and cover — spinach germinates in the dark, unlike lettuce, which wants light on the seed. Space seeds roughly 3–5 cm apart if you want to skip thinning later, or scatter more thickly and thin once seedlings have their first true leaves.

Keep the compost consistently moist. At a genuinely cool room temperature (60–65°F / 15–18°C), expect germination in 7–14 days. If nothing has come up after two weeks, temperature — not light, not seed quality — is the most likely cause.

A soil thermometer takes the guesswork out of this — spinach’s germination temperature ceiling is specific enough that “the room feels cool” isn’t a reliable substitute for a number.

Light

Spinach doesn’t need intense light — it does its best growth around 5,000–10,000 lux for 10–12 hours a day, closer to lettuce than to sun-hungry crops like basil or tomatoes. A bright but not scorching window is usually enough in the cooler months; in summer, a spot with a few hours of shade during the hottest part of the day helps keep both temperature and day length in check.

If your window can’t deliver 10–12 hours of usable light in winter, a modest grow light on a timer fills the gap — just keep the timer at 12–14 hours per the bolting warning above, not the 16-hour ceiling recommended for higher-light crops.

Harvesting

Two approaches work, and which one suits you depends on how you sowed:

Cut-and-come-again (thick sowing): once leaves are 7–10 cm, cut across the whole tray with scissors, leaving about 2 cm of stem and the growing crown intact. It regrows for two or three more cuts before the flavor turns bitter and it’s time to resow — the same rhythm as cut-and-come-again lettuce.

Outer-leaf picking (thinned, individual plants): snap or snip outer leaves at the base once they reach 8–10 cm, always leaving the small center leaves to keep growing. This keeps a single planting productive for longer than a full-tray cut, at the cost of a smaller harvest per pick.

Varieties worth knowing

“Spinach” on a seed packet can mean true spinach (Spinacia oleracea) or one of two heat-tolerant substitutes that aren’t botanically spinach at all but cook and taste similarly. If your only bright window also happens to be a hot one, the substitutes solve a problem true spinach can’t.

Variety	True spinach?	Heat/bolt tolerance	Notes
Bloomsdale (savoy) Classic choice	✓Yes	Low	Crinkled, dark leaves, the flavor most people expect. Bolts fastest of this group in a warm spot.
'Space'-type hybrids	✓Yes	Moderate	Smooth, flat leaves bred for slower bolting. A safer pick for a windowsill that runs warm.
Malabar spinach	–No	High	A tropical vine, not related to true spinach. Wants warmth and can climb — needs a stake or trellis. No bolting problem at all.
New Zealand spinach	–No	High	Sprawling, thick-leaved, genuinely heat-loving. Milder flavor than true spinach and doesn't bolt the way it does.

Heat/bolt tolerance is relative, based on each variety's known growth habit — not a lab-measured figure. True spinach types will still eventually bolt in sustained heat and long light regardless of variety.

Feeding and watering

Keep the compost evenly moist; spinach’s shallow roots dry out faster than they let on, and a tray that dries out completely tends to bolt in response, the same stress reaction lettuce has. After the first cut, a half-strength balanced liquid feed every two weeks supports regrowth without pushing excessive leaf growth that outpaces the plant’s roots.

Common problems

Nothing germinates — almost always temperature. Check the compost isn’t sitting above roughly 70°F (21°C), and consider the pre-chill trick above.

Bolting a few weeks in, tall thin stem with a flower spike — heat, long light, or both. Move the tray somewhere cooler, cut the light schedule back to 12–14 hours, and treat this planting as done; a bolted plant’s leaves turn bitter and won’t reverse.

Yellowing leaves, otherwise healthy-looking plant — usually overwatering or a pot without adequate drainage. Let the top of the compost dry slightly between waterings.

Small pale flecks or fine webbing on leaves — spider mites, more common on plants kept too warm and dry. See common indoor plant pests for identification and chemical-free treatment.

What to expect

At a genuinely cool spot with 10–12 hours of decent light, figure on 7–14 days to germinate and 40–50 days to a first proper harvest — slower than lettuce, but with a texture and flavor lettuce doesn’t have. If your window runs warm no matter what you try, don’t fight it: Malabar or New Zealand spinach will give you a very similar plate without the bolting fight, and they’re a better match for a hot, bright sill than true spinach will ever be.

If spinach’s temperature requirements don’t suit the spot you have, the beginner setup checklist covers matching crops to your actual conditions before you buy seed, and 15 vegetables that grow without direct sunlight has more low-light options if your window is the limiting factor rather than the heat. If bolting is the real dealbreaker for your setup, kale sidesteps it entirely — it tolerates a long grow-light schedule without running to seed, at the cost of a slower start and a deeper pot.