Growing Lettuce in Warmer Conditions
Updated: Mar 1, 2019
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Heat is the primary concern for growing lettuce, and can affect your efforts from the germination stage through the harvest. Ideally, temperatures of about 18-22˚C is when lettuce grows well in the western coast of India, but with a little care you can compensate for conditions of approximately 25-30˚C which are predominant in the winter along India’s western coast.
Growing lettuce in cool temperate conditions is pretty easy, but when you are in warm humid conditions like Goa, this king of salad leaves needs some extra care
“Growing lettuce in cool temperate conditions is pretty easy, but when you are in warm humid conditions like Goa, this favourite of salad leaves needs some extra care.”
CHOOSING THE RIGHT VARIETIES First, select the right varieties of lettuce to grow – heading lettuces like iceberg are a very long shot. Instead focus your attention on the leaf lettuces and romaine lettuces. Some varieties are more heat tolerant than others and you will need to check that their seeds are easily available in India too.
We’ve found the following varieties more productive in Goa’s conditions and seeds are easily available too (check with The Seed Store)…
Salad bowl (green)
Red salad bowl
Marvel of 4 Seasons
To begin with, you should germinate your lettuce in semi shade conditions, so that germination is not badly affected by the hot sunlight. The optimum temperature for lettuce is less than 20˚C, so you should expect germination to be in the 60% range if you are planting early at about 25˚C (before the cooler weather occurs).
CAREFUL WITH YOUR NURSERIES You need to take care that the soil in your nursery beds or pots is really well prepared – soft loamy soil, well drained by using sand or coco soil and old compost that is well decomposed should be used. Do not cover with too much soil, just 2-3mm is fine and do not over water. A fine layer of moss on the soil means that over watering is occurring, and cracks in the soil surface mean that it’s probably too clayey.
Usually the lettuce seeds take 3-5 days to germinate and will have light green leaves. Once the germination happens, the lettuce saplings need more sunlight for at least 3-4 hours in the morning. If they don’t get this, they will tend to become lanky and will tend to be weaker and susceptible to excessive shock while transplanting. Evening sunlight is usually harsher so try and plant in a way that your beds are protected then.
Regulate the sunlight availability for the saplings by either moving your pot nursery or by removing the shade net from beds (making your shade net flaps easily removable is a great idea. Purchase the 50% variant of shade net for use your lettuce bed nurseries and for when the final transplanting will happen in beds.
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PREPARE SAPLINGS FOR TRANSPLANT Prepare the saplings for transplanting by reducing the watering by 20% from day 15 onwards, and then don’t water for 48 hours before the transplant. Just 30 minutes before you pull them out; water them very well so that they can stock up on water.
Transplanting should always be done about 21-25 days from sowing, at the 4-5 leaf stage and when the sun is low in the evenings (after 4 PM). This substantially increases the chances of the lettuce surviving the heat of the day without going limp. It’s a good idea to mulch your well manured raised beds with dry straw before transplanting, but make sure that you create a gap in the straw to prevent contact with the transplanted sapling.
Scoop out a shallow basin of soil in the beds, and put in a handful of manure before you transplant the sapling in. This allows water to be soaked in better into the roots without soaking the leaves excessively.
Provide shade with a shade net for the first 5-6 days until the transplanted saplings have recovered from the shock (leaves aren’t looking limp anymore and the plant is looking healthy). The kind of structure that you choose to use will depend on the direction of the sun.
Once this stage has been passed the lettuce plants will usually grow well unless it gets unusually warm.
In case you have a problem with caterpillars or grasshoppers you can spray either a neem oil or cow urine spray (5% diluted solution in water). Make sure that this is done at least a week before you are harvesting.
To download this as a printable PDF, click here
(c) Prepared for Growing Vegetables Organically 2013 Edition by Miguel Braganza and Green Essentials.