City Gardening By Bio Green Team Share Tweet Pin Share The gardening year starts with lettuce … and ends with lettuce. Not just in the field, but also in greenhouses and cold frames. Lettuce is a collective name for mostly fresh and prepared leaves of various plants. When one hears mention of a garden salad, one thinks immediately of lettuce. From March until Autumn, you can sow the required amount of lettuce every 14 days. Of course, the differences in each of the varieties should be taken into account. The first plants should be purchased in February from a garden centre. There, they have more light during the germination stage and are thus more stable than when bred in a room. From the end of February you can then plant them in a cold frame or in an unheated greenhouse. They are set in reasonably dense arrangements, 20 cm X 20 cm arrays are best for most varieties of lettuce. Early in the year you should also use a black mulch foil, as it helps to keep heat and moisture in the ground. Young plants are usually first cultivated in peat pots. Lettuce must never be planted too deep, otherwise head formation will be delayed and fungal diseases will occur more frequently. Airing is hardly necessary, as the water requirement for most lettuce varieties is low. However, from 18 ° C upwards, your plants should be well-ventilated. Initially, it will take a short time for air exchange, but even cold outside air will not hurt these sturdy plants. Once the plants are firmly rooted, even night time frosts will not cause any problems. Paraffin can be used as a great source of protection against the cold in the first few days, by heating the greenhouse directly over the plants. The Green Guard mini-gas heater also offers protection in spring, the energy consumption of this device is low and plant growth is accelerated enormously. Also to note: lettuce, like many plants, should not be initially kept too wet or else it will have problems developing enough roots. Black mulch film, available from Biogreen, is also a great way to keep residual heat in the ground – the foil is even biodegradable! Where the lettuce comes from The head of lettuce plants is created by a compressed shoot. The two main garden salad types are the well-known Butter and Iceberg varieties. Butter lettuce has rather soft leaves, whereas the Iceberg has relatively firm leaves. Between both of these, there also exists a variety known as Butter Head lettuce, which has somewhat soft, but also somewhat firm leaves. The leaves mostly plume from a delicate green to a reddish brown. The archetype of a classic garden lettuce can also bring to mind the Prickly Lettuce variety (Lactuca serriola), which is often found as a steppe plant in southern Europe, the temperate West Asia, up to northern India and northern Africa. The breeding of each variety also causes each to develop its unique characteristics for example, the summer varieties can either be short-day plant or a day-neutral plant. Some others are particularly heat-tolerant or resistant to lettuce aphids and / or powdery mildew. There are varieties which prefer an early start to the season and other varieties which are better suited for autumn and winter. At present over 100 different varieties are available. You will just have to try them all! This has another advantage, as you can choose a variety of species for year-round cultivation! When it comes to lettuce culture, you should always make sure that every 2 to 3 weeks new seeds are sown. For each person, about 20 plants are recommended. Harvesting begins well before the heads are completely firm, when only the last heads are fixed, then the “new ones” begin to shoot again. From planting to harvest, it takes about 5 – 7 weeks, depending on the season. Always plant the salad quite high in the soil, otherwise the bottom leaves can quickly rot. Salad culture Lettuce seeds should be sown from February / March until Autumn (in the northern hemisphere). Lettuce requires low temperatures for germination, which are present during cooler nights. If the soil temperature stays above 18 to 20 ° C at night, it will either grow rather slowly or not at all. Even for certain varieties which suit warmer months, sowing may only been done in the cool hours of the evening. After sowing, the soil temperature can be lowered by slightly watering. As soon as the first leaves of the seedlings appear, the plants should be separated. When sowing with single corn seeds in multi-pot plates you do not need to do this however. The germination duration is between 4 to 30 days, depending on the variety and temperature conditions. Only when four to five leaves have formed, should the plants be planted with bales in the field. Aim to air the plants out slightly more and more and to have them eventually planted during a cloudy day. If you do not want to wait too long, you can also cover the plants with fleece or some sort of cover. Plant all varieties in the garden in a 25 cm x 25 cm array. The varieties planted in the greenhouse and cold frame should also be planted nearby to one another. Lettuce is fairly self-compatible, meaning that it can be planted easily in places where it has previously grown already. Only the nutrient supply must be taken care of here. However, be aware that lettuce is sensitive to salts, so mineral fertilisers can burn it easily. A low-strength liquid fertiliser, not poured over the leaves, may be best. As mentioned, lettuce must never be planted too deeply and take care that they are not over-watered and that the leaves are dry going into the nighttime. Just like in a greenhouse,cold frames can help you to optimise the cultivation of lettuce, from the beginning of the season, right through to Autumn. Diseases and pests Lettuce can easily suffer from rot, which can be avoided by ventilating the plants when they are still young. Many species of aphids can also be a problem for lettuce, yet they are easily controlled with biological means. For film culture, first remove the film before the formation of the lettuce head. All lettuces from the family of Lactuca sativa var. Capitata contain a white milk juice in their stems, which therein contains the bitter substance lactulin. You can easily see it flow out when the plant is cut. This gives the lettuce its pleasantly mild to slightly bitter taste and helps to support our digestion with its ‘stimulating’ effect. Upon contact with air, the originally white juice at the interface turns brownish, which makes it possible to determine the freshness of the head of the lettuce. Fresh from the harvest lettuces are rich in vitamins, minerals and fibre, as well as low in calories and rich in appetising substances. Lettuce should always be cut as fresh as possible, prepared as soon as possible and eaten immediately afterwards. Was lettuce tastier in the past? Whether this is really the case is still somewhat contentious, however older varieties usually have larger heads with soft leaves; today, other characteristics are have been assigned more importance. Rapid growth, resistance to disease, a closed but small head which makes for easy processing – when cutting off the trunk, the head disintegrates into leaves of equal size. The original version of this article was published in the Greenhouse Post, issue 12/2015, text and image: Jörn Pinske.