Most lettuce varieties are quick and easy to grow and produce a harvest within a month or two. Lettuce does NOT like hot weather. Therefore, you can only grow it during the cooler months from May to July. Although it grows faster in full sun, it is one of the few vegetables that tolerates some shade. What’s more, you can grow lots of lettuce in a small space. You can even grow it with other taller plants like tomatoes.
Lettuce growing conditions
Lettuce needs light, free draining soil that’s rich in organic matter. When it gets enough water and food, it grows faster and tastes better. Lettuce has shallow roots, so it dries out easily! It also gets stressed when not frequently watered making it tough and bitter tasting.
Most book written for cooler climates, will tell you that full sun is essential. Full sun is best ONLY when it isn’t too hot. Once the temperatures approach the thirties , your lettuce will definitely need shade!
Lettuce is a crop that you need to experiment with yourself to see which varieties grow best in your soil. If you are planting in warmer months, you may need a heat-resistant variety such as Jericho and oakleaf. The most heat tolerant kinds of lettuce are the open leafed varieties (Looseleaf). There are also differences in the heat tolerance of the open leafed lettuce kinds. Darker lettuce absorbs more sunlight than lighter colours, so it suffers sooner. So, choose light green over dark red.
If you’re planting for consumption, the loose-leafed varieties are the most practical because you can harvest the individual leaves for up to three months.
Preparing lettuce seedlings
The easiest way to grow lettuce is to grow them yourself from seeds. You can either sprinkle the seeds over a bed and rake them in or spread the seeds very thinly along a row planting trays or punnets and lightly cover with soil. Because the seeds are very fine and not easy to spread evenly, you will have to thin your seedlings later.
To thin, cut the surplus lettuce plants rather than pulling them out, so you don’t damage the roots of the neighbouring plants. Lettuce grows very slowly in the beginning and can easily be overgrown by weeds. Therefore, you should avoid planting your seeds directly in the soil. Emerging lettuce seedlings are very vulnerable to all sorts of bugs including grass and leaf hoppers. Plant seeds every two weeks for a continuous harvest throughout the growing season. (Below is information on how to prepare your own heat resistant seeds)
Planting your lettuce
When they are ready for transplanting, handle them very carefully to minimize the transplanting shock. Ideally you don’t disturb the roots at all. Only transplant lettuce in the late afternoon to give them the longest possible time to settle in, before they have to cope with the sun and heat.
If you grew your lettuce seedlings in shade or semi shade you need to sun harden them before transplanting them. Harden them for a couple of hours the first day, longer the next and so on. The cooler the weather, the better your chances to successfully transplant your lettuce.
Leaf lettuce: Plant 10cm apart.
Cos and loose-headed types: Plant 20cm apart.
Firm-headed types: Plant 40cm apart.
Your rows of plants should be 30 to 40cm across.
Growing Lettuce Plants
As already mentioned, lettuce needs to grow fast to taste good, so keep up the water and nutrients. If your soil is sandy or the weather is very hot, you will need to water daily. Because lettuce have a very shallow root system, stick your finger in the soil to check for water. If your finger doesn’t find any water, neither will the lettuce!
If your lettuce grows slowly despite having plenty of water, then it needs more food. Ideally you planted your lettuce in a well prepared bed that has lost of organic matter and compost in it. If not, then you need to supply extra nutrients, especially nitrogen. The problem is that too much added nitrogen makes plants sappy and weak and very attractive to bugs. Therefore repeated small doses of fertilizer are better than one big dose. (A classic high nitrogen fertilisers would be chicken manure.)
Lettuces need some shade in hot weather. However, you shouldn’t plant them in deep shade, like under a tree. They will just grow into pale, leggy things with few leaves on them. Other options are companion planting between taller plants such as capsicums/peppers or eggplants and staked tomatoes.
If you get surprised by a heat wave, you can always cut leafy branches somewhere and poke them in the ground next to your lettuce to shade them.
Problems when growing lettuce
Nearly all problems you may encounter when growing lettuce are caused by hot weather. The most common problem, apart form the plants bolting to seed prematurely, are brown edges on the leaves. This happens especially if you get very hot weather after a cool spell.
Bugs that chew on your lettuce are often a symptom that your plant is not as happy as it could be. Bugs are attracted to stressed plants. So in the end it comes down to everything that I explained above. Enough water, enough nutrients, just the right amount of shade, and… Accepting that lettuce is not a tropical vegetable!
Harvesting your lettuce
You should harvest your lettuce young and tender, just before maturity in the morning before leaves have been exposed to sun. Mature lettuce gets bitter and woody and it will bolt(send up that long flower stalk) quickly, so check your field everyday. You can harvest leaf lettuce by simply removing outer leaves so that the center leaves can continue to grow. You can harvest butterhead types by removing the outer leaves, digging up the whole plant or cutting the plant about an inch above the soil surface. Crisphead lettuce is picked when the center is firm.
Preparing your seeds for next planting season
If you’re just starting out, plant different types of lettuce, and then save the seeds from those varieties that lasted the longest before flowering. When your lettuce sends up a long flower stalk, it’s too bitter to eat. (You’ll have to be very observant and take notes).
Lettuce flowers mostly self pollinate. If you grow several varieties next to each other you will end up with about 95% of seed that is just like the parent, and 5% of surprises. And you never know, one of those surprises may be even more heat tolerant! Just save the best seed every year, and within a few years you have the most heat tolerant lettuce, perfectly adapted to grow in your soil, something you’d never be able to buy.