Lettuce, Spinach and Kale in Containers
Salad leaves are the highest-value crop for a small container garden. They need little space, tolerate partial shade, and can be harvested repeatedly from a single sowing. They also bolt, bitter and fail in predictable ways that are easy to avoid once you know the triggers.
Cut-and-come-again versus whole heads
Two approaches, and they suit different situations:
- Cut-and-come-again: sow loose-leaf varieties densely, cut the whole plant 2–3 cm above the soil when leaves reach 8–10 cm, and let it regrow for two or three further cuts. More total yield from less space, and harvest begins two weeks earlier.
- Whole heads: grow hearting varieties (Cos, butterhead) at proper spacing for a single large harvest. Better for a big salad at once, slower, and more vulnerable to slugs and heat.
For containers, cut-and-come-again wins almost every time.
Choosing varieties for pots
| Crop | Good container varieties | Sowing to first cut | Notes |
|---|---|---|---|
| Lettuce | 'Salad Bowl', 'Little Gem', 'Lollo Rossa', 'Red Salad Bowl' | 30–40 days | Loose-leaf types are far more forgiving than hearting |
| Rocket | Wild or standard rocket | 25–35 days | Bolts within days in hot weather; sow little and often |
| Spinach | 'Perpetual', 'Beet Leaf' types, Malabar spinach for summer | 40–50 days | Needs shade and steady water to delay bolting |
| Kale | 'Dwarf Green Curled', 'Nero di Toscana' | 55–70 days | One plant crops for months; improves after frost |
| Chard | 'Bright Lights', 'Fordhook Giant' | 55–65 days | Most heat-tolerant of the group; very reliable |
| Mizuna, mizuna greens | Any | 25–30 days | Excellent cut-and-come-again, mild peppery flavour |
| Mustard greens | 'Red Giant', 'Green Wave' | 25–35 days | Fast and productive; gets hot in summer |
Containers and sowing
A 4–6 L container, 15 cm deep, is enough for a cut-and-come-again sowing; a trough 60 cm long gives salad for two people. Fill with fresh multi-purpose mix and firm it lightly.
Sow thinly. This is the step people get wrong: lettuce seed is tiny, and a pinch becomes a carpet. Two practical methods:
- Shallow drills: draw lines 1 cm deep and 10 cm apart with a stick, and space seed roughly 1 cm along the line. Thin to 5 cm after two weeks.
- Broadcast for cut-and-come-again: scatter lightly across the surface, cover with 3 mm of mix, and thin to about 4 cm spacing once germinated.
Cover with 3–5 mm of mix, press down gently, and water with a fine rose so you do not displace seed. Germination takes 5–10 days at 15–20 °C.
Lettuce seed will not germinate reliably above about 25 °C — it goes dormant. In midsummer, sow in the evening, keep the container in shade until germinated, and water the surface daily. Or simply skip sowing lettuce in July and August and grow chard, kale and Malabar spinach instead.
Water and feed
Shallow-rooted and mostly water, salad leaves need consistent moisture. A dry spell makes leaves bitter and triggers bolting. Check daily in summer; a 5 L pot in sun may need water twice a day.
Feeding matters less than for fruiting crops, but a weekly half-strength high-nitrogen liquid feed noticeably increases regrowth speed after each cut. Slow-release granules mixed in at sowing are enough for a single cut-and-come-again cycle.
Stopping bolting
Bolting — running to seed — makes leaves bitter and ends the harvest. The triggers are long days, high temperature and root disturbance. Countermeasures:
- Grow in afternoon shade during summer; part-shade positions actually extend the season.
- Choose bolt-resistant varieties and sow every three weeks so a fresh sowing is always ready.
- Keep roots cool and moist; mulch helps, and pale containers reflect heat.
- Pull bolted plants immediately and resow — bolted lettuce is not worth eating.
Harvesting
Cut in the morning when leaves are turgid and cool; they keep longer. Use scissors, cut 2–3 cm above the growing point, and take no more than a third of the plant at once. For kale and chard, pick the outer leaves continuously and leave the centre alone — a single plant will produce for four to six months this way.
After two or three cuts, leaf lettuce declines in quality. Clear the container and resow; the whole cycle is barely six weeks.
A continuous supply
Three containers, staggered by three weeks, is enough for a steady household salad supply: sow container 1 in week 0, container 2 in week 3, container 3 in week 6, and clear-and-resow container 1 in week 9. In winter, move the operation to a bright windowsill and switch to hardy types — rocket, mizuna, winter lettuce and chard will produce slowly but steadily indoors.
Common questions
Why has my lettuce turned bitter?
It is either bolting, triggered by heat and long days, or it was under-watered. Harvest earlier, move containers into afternoon shade, and sow more frequently in hot weather.
How many times can I cut a lettuce plant?
Usually two or three cuts before quality declines. After that, clear the container and resow — the whole cycle is about six weeks, so a replacement is always close behind.
Why are my seedlings collapsing overnight?
Damping off, a fungal problem encouraged by wet surface mix and poor airflow. Reduce watering, thin seedlings for airflow, and sow into fresh mix next time.
Do salad greens need full sun?
No, and they often prefer not to have it. Two to four hours is enough for lettuce, rocket and spinach, and partial shade noticeably slows bolting in summer.