Lettuce is generally a cool-season crop, but there are heat-tolerant and bolt resistant varieties to grow in the warmer months too. Apart from maybe the hottest months, you can grow lettuce all year around in your Sprout, and the key is to sow little and often! If you sow every 3 weeks you should have a constant supply. It usually takes somewhere between 40-90 days from sowing to harvest, depending on the varieties and conditions.
Types of lettuce
There are many different types of lettuce and they have either loose or compact growing leaves.
Loose leaf lettuce – form loose, frilly or smooth leaves that can be green, yellow, red or purple and are the quickest to harvest, some after just 40 days.
Butterhead lettuce- form loose round heads with a soft texture and delicate flavour. They generally take 60-85 days to mature and are sensitive to high and low temperatures.
Cos or Romaine lettuce – form an upright cylindrical or oval head that takes around 80 days to mature. They are not very sensitive so are easy to grow.
Iceberg or Crisphead lettuce– form a firm and compact head of overlapping leaves. They can take up to 90 days to mature and need more space than the other types. They can also be more sensitive to irregular watering than the other types .
Because lettuce is a cool-season crop it is best sown in the winter, spring and in the autumn. For a summer harvest, heat and bolt resistant varieties must be used. When growing lettuce in your Harvst Sprout, it’s important not to keep the tray too warm as it can make the lettuce bolt. The ideal growing temperature is 15-19°C but lettuce seeds germinate from as cold as 2°C to 20°C. Outside this range they will struggle and it is also worth noting that they take longer and are more erratic to germinate when the temperatures are cold. However, the seeds tend to germinate in around 7-14 days.
Lettuce is fairly easy to grow from seed and can be direct sown or transplanted later. It is a perfect crop to sow in your Sprout as it can stay in there till it matures or be transplanted outside.
Fill a tray with a general peat free multi purpose compost and water it. Sow the seeds a couple of cm apart and sprinkle 0.5cm of compost on top. Press down slightly to make sure that the seeds are in good contact with the compost and carefully water again. If you’re using a modular tray then put 2 seeds per module and thin out if both germinate.
Keep the soil evenly moist until seeds germinate because if they dry out they will most likely not germinate at all. This can be aided with a plastic dome over the tray but it is not a must. As a general rule, the colder the soil the less moisture you need.
Keep the soil evenly moist throughout the growing season as irregular watering can make the lettuce bolt and turn bitter. However, avoid splashing muddy water onto leaves if you can and also keep them fairly well fed.
You can choose from one of the growing options below or do a combination of 2, 3 or 4! The most important thing for all 4 growing options is to not let the lettuce plants dry out at any time. They are shallow-rooted plants that require regular watering but try to avoid splashing soil on the leaves when watering. Having said that, the soil should be moist and not super wet as it can make them rot.
- Baby Leaves: Start harvesting directly from your tray when the leaves are as big as leaves in a Supermarket baby leaf salad bag! If you pick one or two leaves of each plant from the outside, rather than the whole plant, it should keep on growing for a while and give you a few harvests!
- Grow till maturity in your Sprout: When the seedlings have emerged, thin them to 15cm apart for loose leaf varieties and up to 30cm apart for the largest head varieties. This can be done by cutting the rejects with scissors (eat them in a salad!) or carefully using a stick/pencil to loosen the soil and lift the seedling up by its leaves and transplant to elsewhere. Make sure they are big enough to handle before you set out to do this. The compost will only have enough nutrients for a few weeks so you will have to feed the plants with an organic fertiliser throughout the growing season.
- Plant outside: When the seedlings have developed their true set of leaves (not the first set appearing but the second set) they can be transplanted out into your garden. Space them 15-30cm apart depending on the variety. If you have problems with slugs, keep them in your Harvst a little longer. A bigger plant can resist a slug attack much better! When planting outside it is best to make sure that your soil is great before planting by adding well rotten manure or other organic material so that it’s full of nutrients for your plants. When transplanting seedlings, ideally plant out early morning or evening and/or on an overcast day. Avoid planting at peak sun times or on windy days as this can cause sun or windburn which can lead to death!
- Container Grown: Lettuce grow well outside in a container but try to choose one that is at least 15cm wide and tall. As lettuce is heat-sensitive, move containers into the shade on warm days and keep in mind that containers will warm quicker than garden soil in spring and that lettuce absolutely must have constant moisture in the soil. Also, keep in mind that the compost will only have enough nutrients for a few weeks so you will have to feed the plants with an organic fertiliser throughout the growing season.
Lettuce leaves can be harvested as soon as they are big enough to eat and it is up to you if you like the small baby leaves or prefer the larger ones. However, very large leaves can be bitter so harvest sooner rather than later. For loose-leaf varieties, cut the outer leaves and leave the inner leaves to remain and develop. If you are growing Cos or head varieties you should wait till it has formed a firm head and then cut it just above the soil level. In any case, keep an eye out for any signs of bolting and make sure you harvest before that. For the best flavour try to harvest when you need it and eat straight away. Also try to harvest in the cool part of the day so that it does not wilt straight away!
There are many little creatures that love lettuce, but slugs and snails tend to be the biggest problem. If you have a slug and snail problem your Sprout should assist you in keeping them away. Grow them till maturity in the Harvst Sprout and keep any seedlings to be planted out in the greenhouse till they are a little bit bigger as they can withstand an attack better. Lettuce can also be attacked by aphids, flea beetles and leafminers. Aphids are best treated by showering the plants. Flea beetles can be kept at bay by netting and keeping the soil moist at all times. Leaf miners tunnel through leaves and those should simply be removed. Also, look for the eggs on the underside of the leaves!
Use a shade cloth to protect lettuce from hot weather, or move any pots to the shade. If your lettuce leaves have a slightly bitter taste, place them in the fridge for two days or soak them in water with a tiny amount of baking soda for 10min. Rinse them carefully and soak again in water for 10min.
Lettuce botanical name is Lactuca sativa and belongs to the Asteraceae family. Other plants in the same family are surprisingly – daisies, sunflowers, chrysanthemums, asters, dandelions, goldenrod, coneflowers, thistles, artichokes, sunflowers dahlias, marigolds, zinnias, asters, chamomile, chicory, sage, tarragon, ragweed, thistle, sagebrush, and yarrow.
Here are some great varieties but there are many more fantastic varieties to choose from!
- Loose-Leaf: ‘Red Salad Bowl’ and ‘Green Salad bowl’ takes around 45 days to harvest and has beautifully frilled leaves
- Butterhead: ‘All year round’ is a reliable variety forming medium heads with solid crisp hearts.
- Romaine or Cos: ‘Parris Island Cos’ is a very big, sweet and crunchy Cos lettuce that takes around 75 days.
- Crisphead or iceberg: ‘Webbs Wonderful’ has large, wrinkled leaves with a crisp and white heart. It is slow to bolt, and performs reliably.