Application of Hydroponic Techniques in Greenhouse Flowers

Soilless cultivation means cultivating garden plants without soil, instead using water, sand, gravel, slag, sawdust, vermiculite and the like to replace soil as the growing substrate, and using inorganic fertilizers mixed into a suitable aqueous solution as the nutrient source for the plants. Because no soil is used, it does not have the various advantages and disadvantages of soil cultivation; instead, it has the advantages of high yield, good quality, fewer pests and diseases, light pollution, labor savings, and fertilizer savings. At the same time, soilless cultivation does not depend on whether the terrain is high or low, can fully utilize space, and is especially suitable for use in home gardening. Moreover, garden plants grown by soilless cultivation have large flowers, bright colors, deep green leaves, and a long flowering period; it can avoid soil-borne pests and diseases; no organic fertilizer is applied, but inorganic fertilizer is used, which is odorless and clean and hygienic. Recent relevant data show that the edible produce from soilless cultivation per sq m can feed 1 person for 1 year. This shows that soilless cultivation can be applied over the long term both now and for some time in the future, and in a country like ours with many people and little land, it is worth long-term research and discussion. (See Table 1)

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There are many methods of soilless cultivation, which differ in substrate use, preparation and supply of nutrient solution, and control and regulation of environmental factors. Generally there are 3 forms: hydroponics, substrate culture (solid culture), and aeroponics. At present, aeroponics is mainly used for research on plant roots and plant propagation; hydroponics and substrate culture are widely used in the production of flowers, vegetables, and melons and fruits, and in the export of bonsai. Hydroponics and substrate culture are actually much the same in principle; both require preparing a nutrient solution, but the plant material used for fixing the plants differs, and the containers used also differ. In hydroponics, the concentration of the prepared nutrient solution should be somewhat lower, while in substrate culture the concentration of the nutrient solution is slightly higher. Generally speaking, a lower concentration in hydroponics is beneficial to plant growth; as long as the plants do not show deficiency symptoms, do not increase the concentration of the nutrient solution. When the nutrient solution formula required by the plants cannot be mastered in substrate culture, choosing substrate culture makes it easier to succeed. The author will briefly discuss the application of hydroponics in greenhouse flowers.

1 The process and reactions of hydroponics

1.1 Preparation of materials

① Plant materials: 2 plants each of chrysanthemum, Pilea cadierei, Chlorophytum comosum 'Variegatum', foxtail flower, Taxus cuspidata (dwarf yew), and Nephrolepis cordifolia. ② Containers: 6 beakers of 250 mL, 6 wide-mouth glass cups or fruit canning jars, washed and sterilized. ③ Fixing material: foam plastic (polystyrene board). ④ Inert material: nutrient solution.

1.2 Steps of hydroponics

(1) For flowers grown in the ground or in pots, wash the soil off the roots, then disinfect with a 25% carbendazim 800-fold solution, let dry after disinfection, and then place the plants into containers. Cut the polystyrene board to the size of the bottle mouth with equal sides, make a small opening in the middle of the plastic board (or cut it into two halves and make a small opening in the middle), fix the plant, trim a small part of the root system according to the size of the plant, add water to 3 cm below the bottle mouth, fix the plant in the container, and place it appropriately in a slightly shaded place to adapt for a period of time. According to the different characteristics of the plants, the placement position differs; shade-tolerant plants are placed lower, and light-loving plants are placed higher, so that the plants can receive a little visible light. This should be done according to how the plants adapt, generally for a period of 20-30 days (narcissus does not need this long).

(2) Prepare the nutrient solution. Because plants need about 34 elements, 16 of which are main elements. The concentration of macroelements is a few parts per thousand, and the concentration of microelements is a few parts per ten thousand. The macroelements are carbon, hydrogen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, etc.; the microelements are molybdenum, iron, zinc, manganese, boron, etc. The fertilizers prepared are all inorganic fertilizers, which can dissolve in water and are easily absorbed by plants; the water must not contain impurities. There must be no polluted water. The pH of the nutrient solution is generally between 5.5—7; if too acidic, add sodium hydroxide, and if too alkaline, add dilute hydrochloric acid. There are many formulas for nutrient solutions. Based on the reagents currently available for purchase in chemical reagent stores, the following formula is specially selected (see the table below).

(3) After the adaptation period, supplement the nutrient solution. According to different concentrations, add supplementary nutrient solution; above 20°C, during the growing period about 10-20 days per time. Below 20°C, 20 days per time. When left for a long time, replace the nutrient solution about once every 2 months, pour out all the nutrient solution, and add new nutrient solution. Ordinarily, only supplement the nutrient solution in the cup, and maintain a certain scale; do not exceed the scale, which would affect growth.

(4) During the adaptation period, some varieties cannot keep their roots in water for a long time. Among the above varieties, foxtail flower is the most obvious at the root tips, with white flocculent matter appearing around the roots. This white flocculent matter continuously inhibits growth. For Pilea cadierei in water at 10°C, white roots appear in 10 days; chrysanthemum shows white new roots in 12 days; Chlorophytum comosum 'Variegatum', dwarf yew, and Nephrolepis cordifolia have no new roots. After the adaptation period, change the water to nutrient solution; in winter, growth is normal in a greenhouse above 5°C. Below 0°C, the water will freeze, causing the plant root system to be frost-damaged, leading to the death of the entire plant.

2 Experimental analysis

During the experiment, it was also found that some flower varieties are not suitable for hydroponics but are suitable for substrate culture; substrate culture can control water requirements. There are relatively many nutrient solution formulas for hydroponics, and different varieties require different nutrients. During the growing period, the effective concentration of the nutrient solution can be increased; on the one hand, this can supplement sufficient nutrients, and on the other hand, it can promote organ differentiation. During the dormant period, the effective concentration of the nutrient solution can be appropriately reduced. Generally speaking, as long as the plants do not show deficiency symptoms, do not increase the nutrient concentration of the nutrient solution. At different growth and development stages of plants and under different climatic conditions, the requirements for various nutrient elements are different. In late autumn and early winter and in seasons with many cloudy days, the supply of potassium should be increased. Because among the many formulas, it is very difficult to find the most ideal one. The author believes that hydroponics is the development trend of the future. It is easy to manage, saves money, saves time, occupies a small area, does not pollute the environment, and can use some empty bottles and empty discarded containers without drainage holes for planting. For different varieties, the required nutrient solution concentration is different; correctly mastering the concentration to use remains to be worked out through long-term practice.