**6. Glass greenhouses**

Glasshouses are the best protected indoor area for growing vegetables in regions where climatic conditions are unfavourable for their growth and development in either open field or plastic-glazed greenhouses. They are the best environment for controlling the climatic conditions and the mineral feed of the crops during their vegetative period. At the same time, also, the warm season crop vegetative period could be prolonged when compared with growing such crops in open field. Furthermore, the modern glass greenhouses are perfect with regard to applying modern technologies and scientific developments in growing crops. Of course, the economic factor is of utmost importance for commercial crop production. So, both short and extensive financial plans have to be made. Glass greenhouses are built mostly in cold climates, but as they provide the environment where the climatic conditions can be completely controlled, they are also a good choice for growing vegetables even in warm climate regions. Modern vegetable crops growing in glass greenhouses are very intensive from the perspective of capital investments, application of the latest production technologies, know-how, labor, energy, substrate, hydroponics. The greatest issue in modern greenhouses is the high cost of energy. There have been, however, some significant shifts toward reducing the cost of heating. The Venlo greenhouse type [8] is probably the most-built type worldwide and the most economical one among the professional vegetable crop growers. The design of the Venlo greenhouse is suitable for all sorts of crops and under various climatic conditions. This type of greenhouses was developed in the Netherlands and was named after the region and the place of Venlo where it was first made (southeast the Netherlands, toward the German border). The whole region has one of the largest concentrations of greenhouse horticulture.

The Venlo greenhouse is the galvanized steel frame structure, as the best and most durable material that can deal with the weight of the entire greenhouse and the roof frame. The roof frame can be made of aluminium or galvanized steel of various profiles. The roof frame also carries the windows/openings that in the Venlo glasshouse can be opened from both sides and make 20–30% of the total glass

### *Advantages of Growing Vegetable Crops in Modern Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.101469*

surface area. As the frame structure consists of a great number of columns of various sizes and dimensions, there is actually much shade inside the greenhouse that affects the crops. For that reason, it is advisable for the entire frame structure to be perforated and painted in white so as to increase the indoor lighting. The crops that are mostly grown in greenhouses are as follows: tomatoes, peppers, eggplants, cucumber, melons and small watermelons (up 1 kg), lettuce, spinach, grapes, raspberries, blackberries, strawberries, blueberries, and, of course, seedlings of vegetables and flowers and various edible berry fruit. Often grown in greenhouses are also broccoli, cauliflower, leek, bananas, ginger. Actually, all horticultural varieties can be grown in greenhouses, but it would be best to check first how cost-effective it could be, that is, to do a feasibility study. If a feasibility study has to be done as a guaranty for the bank loan or a subsidy, then such a study should be detailed and done by a recognized firm or a consultant. Since greenhouses provide the environment for almost complete control of the selected crop production, the grown crops are safe for human consumption. That means they meet the best standards with regard to both safety and quality. Furthermore, there is a minimal environmental pollution. Other benefits are that the early crops come to market sooner and also, high yields are achieved. For instance, in hydroponic tomato production (on the rockwool growing substrate), the yield can be even up to 100 kg/m<sup>2</sup> , or 1000 t/ha per annum. The fact is that the yield (or the production rate) in the modern glass greenhouse can be 10 times as much as in the open field. High yields are achieved through intensive growing methods and by prolonging the production season. Besides the vegetable quality and the environment pollution reduction, the yield should be high also because of a return of the investment and payments of additional costs. The majority of the glass greenhouses manufacturers put on offer glasshouses and the horticultural production technology, which may provide optimal production under the given market conditions, so that the additional costs would pay out through the earnings from the additional production. Consumers in most of the developed countries expect to find good-quality vegetable produce grown in glass greenhouses on their respective markets. In most cases, it is the improved quality of the vegetable produce that gives a motive for starting the glasshouse vegetable production. For different types of produce and different markets, there are also different parameters for food quality. The quality parameters for the fruit and vegetables required on the market may include the following: taste, flavor, aroma, size, color, stage of ripeness, firmness or softness—texture, shelf life, the absence of any spots or defects, minimum or no waste, no signs of pests or disease, with or without leaves, and many more. One of the most important standards in the primary agricultural production, which is also a quality guarantee of both the primary agricultural production and the produce itself, is the GLOBALG.A. P. standard/certificate. According to the construction and engineering characteristics, appearance and purpose, there are several types of glass greenhouses that could be single-span, multi-span, lean-to, gabled.
