Crop type: Lettuce
Lactuca sativa ‘Lobjoit’s Green Cos’
Common name: Cos lettuce ‘Lobjoit’s Green Cos’ AGM
Crop slug: lettuce
This Allotment Pro editorial draft summarises the cited RHS cultivar profile. Check the source and adjust cultivation decisions for local conditions.RHS cultivar profile
1 - Overview
‘Lobjoit’s Green Cos’ is a leafy biennial normally grown as an annual vegetable. This classic cos lettuce produces large, firm hearts with deep-green leaves and a crisp texture from spring to autumn, according to sowing date.
The parent RHS guide describes it as a cultivar many growers consider the best cos variety, with dense, crisp, compact heads. Its combination of substantial head size, upright form and rich green colour distinguishes it from dwarf cos lettuces. It holds the RHS Award of Garden Merit.
2 - Size
- Ultimate height
- 0.1–0.5 metre
- Ultimate spread
- 0.1–0.5 metre
- Time to ultimate size
- 1 year
This is a full-sized cos, so provide enough space for the upright head to broaden and firm. Good spacing also exposes the lower leaves to moving air and makes it easier to inspect for pests.
3 - Growing conditions
- Suitable soils
- Chalk, clay, loam or sand
- Moisture
- Moist but well-drained
- Soil pH
- Acid, neutral or alkaline
Grow in fertile soil that retains moisture without remaining saturated. The large heart develops best with steady, uninterrupted growth, so incorporate mature organic matter before planting and water whenever the shallow root zone begins to dry.
4 - Position and hardiness
- Light
- Full sun
- Aspect
- South- or west-facing
- Exposure
- Sheltered
- Hardiness
- H2 — tolerant of low temperatures but not surviving prolonged freezing
A sunny sheltered plot encourages dense upright heads. Protect early and late crops using cloches or biodegradable horticultural fleece. Ventilate covers during mild weather to prevent humid conditions around the close-packed leaves.
5 - Colour and seasonal interest
Tall, broad, deep-green outer leaves stand around a paler but still green firm heart. The leaf surfaces are crisp and substantial rather than frilled or deeply lobed, and the mature plant has the vertical oval silhouette associated with a large cos. Harvest before the centre stretches; an edible crop should carry no flowers or seed heads.
6 - Botanical details
- Family
- Asteraceae
- Native to Great Britain and Ireland
- No
- Foliage
- Deciduous
- Habit
- Clump forming
- Name status
- Accepted
Genus
Lactuca includes annuals, biennials, perennials and shrubs with alternate leaves and milky sap. Garden lettuce cultivars are selected for edible leaves and loose or hearting forms and are usually harvested before flowering.
Safety
No specific handling warning is listed on the exact RHS profile. Remove damaged leaves, wash carefully between the close leaf bases and follow normal food-hygiene practice before eating.
7 - How to grow
Cultivation
Grow in full sun on fertile moisture-retentive, well-drained soil. Sow a short row every fortnight to maintain continuity rather than creating one large glut. Thin seedlings or transplant module-raised plants promptly, keeping each central growing point above soil level.
Protect early and late sowings with cloches or biodegradable fleece. Keep the bed weed free, water at soil level in the morning and maintain even moisture while the large heart fills. Cut when the upright head is dense, firm and crisp, before heat or age causes the centre to elongate.
Propagation
Propagate by seed. Sow thinly in shallow drills or individual modules and avoid very hot seedbeds, which can inhibit germination.
Suggested locations
- Vegetable plot
- Sheltered allotment row
- Raised bed
- Large deep container
Pruning
No pruning is required. Remove only yellow or damaged outer leaves and harvest the entire head when mature.
Pests
May be susceptible to slugs and snails. Inspect beneath the lower leaves and use suitable barriers or biological controls where damage becomes persistent.
Diseases
May be susceptible to grey mould and downy mildew. Avoid crowding, water early at soil level, ventilate crop covers and remove affected material promptly.