LETTUCE PRODUCTION IN GREENHOUSES
Lettuce (Lactuca sativa) has different sowing times, as follows: Early-spring sowing, late-spring sowing, summer growing, autumn-winter sowing and winter growing. Lettuce is grown in outdoor fields and in glass and plastic greenhouses. Growing in a covered location begins in the second half of September and last until the end of April. Late-spring sowing is typical for this period of the year, with sowing taking place in early December and early January. Lettuce planted in this period arrives in late March and early April. Lettuce typically has a short vegetation period of 50-120 days, depending on the sort and growing conditions. The optimal temperature for growing lettuce ranges from 18 to 20 Co, while temperatures of between 10 and 15 Co give satisfactory results. Optimal soil moisture should be about 70-75% FWC. Special care should be taken to prevent excessive moisture, given that this creates the conditions for the development of rot to which lettuce is especially sensitive.
Lettuce seedlings are grown in peat blocks and containers. Lettuce can be grown from ordinary or from processed seeds. Processed or pelleted seeds are much more expensive than ordinary seeds, which play a substantial role in the increasing costs of production itself. On the other hand, using ordinary seeds results in small-scale germination and it is difficult to get uniform seedlings.
In order to achieve faster and more uniform germination and sprouting of plants, Agrounik recommends that lettuce seeds are treated prior to sowing with the microbiological growth stimulator Slavol S. Application is very simple. The seeds are immersed in Slavol S solution for half an hour. When the seeds dry, sowing can commence.
The growing of lettuce seedlings takes 4-6 weeks, depending, of course, on the growing conditions. This takes 6 weeks during winter. For seedlings in blocks, attention should be paid to separate the blocks, so the root system grows downwards, not sideways. The seedlings are ready for planting when they have 4-6 normally developed leaves. Seedlings grown in containers should be planted more deeply, i.e. the entire root that has grown should be in the soil. As for seedlings from nutrient blocks, they are not placed completely into the soil; rather 1/3 of the height of the nutrient block should be gently placed into the ground.
Prior to transplanting, the soil should be treated with Uniker (5 l/ha), which, thanks to its composition, encourages the better progression of plants after transplanting and ensures the optimal provision of the nutrients that are essential for the plant.
As for the topdressing for lettuce, foliar feeding in combination with protective agents is carried out using a drip and sprinkler system. Agrounik’s recommendation is to apply Slavol in a concentration of 100-200 ml to 10 l of water or 1-2 ml/m2 through a drip system. The seedlings should be treated 1-2 times a week, and after transplantation Slavol should be applied in 7-10 days. Application of Slavol promotes plant growth, photosynthesis intensity, increases plant resistance to disease and eliminates the negative impact of pesticides.