COMMERCIAL CARNATION GROWING ON ROCK WOOL MATS IN DENMARK Andreas Bjerggaard, Danish Market Growers' Association, Advisory Service, Anker Heegaards Gade 2, 1572 K0benhavn V, Danmark Abstract The use of rock wool as a growing medium has become a common practice in Danish glasshouse cultures during the last years. Until today no scientific work has been published regarding carnation growing in rock wool. This paper is based upon practical experience in Danish carnation growing from single beds with rock wool compared with soil to entire greenhouses covered with rock wool mats. Materials, methods, difficulties and advantages are described. Introduction Rock wool was first suggested as a growing material in 1968 (Bagge Olsen 1970) and especially for container growing in nurseries (Mosegaard 1970). Trials were carried out in trees and shrubs (Hornum 1971), and the Danish Rock Wool firm was producing a new type of wool, named "Grodan", absorbing moisture in contrary to the original insulating material. Since then rock wool has been tried and used in several glasshouse cultures, and the areas of rock wool growing in Denmark are still increasing (table 1). Table 1 - Increase in rock wool growing in Denmark brutto glasshouse area in_m^ Year cucumbers tomatoes roses carnations 1970 100 1971 100 1972 100 1973 2000 1974 16000 4000 4000 100 Xif ILTO 1975 65000 20000 4000 500 1976 135000 120000 6000 2000 1977 160000 140000 8000 12000 \ o The first commercial test in Denmark was only consisting of one single bench compared with traditional growing in steamed soil. During a 3 years culture there was more than a 10% rise in production and a significant better quality on the rock wool bench compared with steamed soil, even with the same watering and fertilisation on rock wool as normal in the soil benches. Acta Hort iculturae 71, 1977 Carnations 215
Materials The first rock wool growing was carried out in granulates. Like most of the glasshouse cultures today carnations are grown on rock wool mats, placed on plastic films to a- void disease infection from the soil. The first year a slight curving of the mats from side to side was used (figure 1). In order to get more even water distribution and in order to avoid water in the path, next year the film and the mats were placed straight horizontal (figure 2), but then difficulties were caused by slow air change and unsufficient drainage. In the carnation cultures today we are placing two rows of slabs, 40 x 90 x 7,5 cm, in a i m wide bench slightly sloping towards the center, where the plast film is bent down in a narrow draining ditch (figure 3). Films of 0,05 to 0,07 mm thickness are normally used, and milk white or black types are preferred, where weeds are expected to grow under clear films. Planting The young plants are only placed on the surface of the slabs, supported by the pre-drawn nettings. Rooted cuttings directly from the propagation benches may be used, if they are well rooted and grown in a mixture of perlite and peat. Naked roots and perlite alone cannot draw sufficient water from the rock wool, and in such cases a supply of peat at the plant setting is needed. To dig the cuttings down in the mat surface is mortally dangerous, causing stem rot immediately. Pot cultivated plants, for instance in peat or paper pots, are easy to place. This year some growers are propagating carnation cuttings in rock wool blocks, and we are looking forward to see the results. Wa tering The rock wool, built of very fine hairy particles, has a pore volume of about 97%. When saturated with water and placed on plast, the 7,5 cm thick mat will have an air volume left less than 15%. During winter conditions and while young plants are rooting, there may be a lack of oxygene, if the drainage is too poor (Willumsen 1971). Under such circumstances the use of nitrite test strips is recommended. The high amount of water is kept in relatively large pores, so almost the entire water contents is available for the plant roots. The easy movement of the water in the mats makes the underlaying film necessary, and if the house has a lengthwise slope, a slight distance between some of the slaps is necessary, or plast strips must be placed between the slaps, to avoid uneven moisture through the benches. Watering at short intervals may help the air shift. Nozzles as well as trickle irrigation can be used for water supply. 216
Nutrition Rock wool is nearly an inert material, and a complete nutrient solution has to be used constantly. Only a slight amount of basic oxides may in the start cause some difficulties, if the ph value is not carefully corrected. A group of Danish scientists and specialists in hydroponics have shown new ways in fertilizing (Nielsen 1976), and their results have been utilized not only in water culture, but also in rock wool growing as well as in traditional soil growing. In order to maintain a high nutrient level in the growing medium and to avoid accumulations during the culture, a special formulation of the feeding solution for each species in question is maid, proportional to dry matter analysis from entire plants (Hansen 1976). In practice we have realized that dry matter analysis of entire carnation plants are showing too high K:N ratio. If wooden parts are sorted away, samples of green matter only have shown proportions usable for the carnation formulation. Several samples have shown identical figures, unless under special conditions. (At calcium deficiency we have found a K:N ratio 1:1). When N is set to 100, we are at the moment using following proportions for carnations: N P K Ca Mg S Fe Mn B Zn Cu Mo 100 25 200 110 18 20 1,2 1,0 0,4 0,06 0,06 0,04 Normally this formulation is calculated up to a strength about 1 to or a conductivity near 2 mmhos in the solution. The quality of the raw water is tested, and the formulation is corrected according to water contents and quality (table 2). Table 2 - Formulation of feeding solution for carnations, _sample from practice N P K Ca Mg S Fe Mn B Zn Cu Mo wished contents in ppm = mg pr,. 1 125 31 240 130 21 25 1,5 1,25 0,5 0,07 0,,07 0,05 raw water analysis: 8 0 13 93 18 35 0,2 0, 00 0,1 - supply of fertilizer: 113 31 227 37 3 0 1,3 1,25 0,04 0,07 0,,07 0, 05 Chemicals, 1000 liter: KN0 3 (39% K,14 % N) 513 g Fe--chelate (9% Fe) 16,0 g Ca(N0 3 ) 2 (21%Ca,1 5 %N)178 g MnSO. (25% Mn) 5,0 g 4 KH 2 P0 4 (29% P, 23% K)100 g Solubor (20% B) 2,0 g HN0 3, 62%(14% N) 75 ml ZnSO. 4 (23% Zn) 0 3 g Fosmagnit CuSO (25% Cu) 0,3 g (4,4% Mg, 12,4% P) 50 ml Na 2 MoO, 4 (46% Mo) 0,125g 201
Phosphoric acid and/or nitric acid are used to lower the ph /alue to 5,8-6,0 in the nutrient solution. The rather high requirement for calcium may give some troubles, where the calcium contents in the water is low. Then alternating feedings between complete solutions a Ca-nitrate may be necessary, or the mixing equipment has to work from two sources with double injection. Diseases Until now there has been no evidence, that disease infections might be worse in a rock wool culture than in soil culture, provided that the young plants are healthy. In one case, where plants were infected, we found that the disease had spread much more rapidly in rock wool than in soil, but using fungicides we found, that it was easier to controle the pests in rock wool, with concentrations reduced to 1/3 of normal concentrations. The concentrations were reduced to avoid plant injuries, and the effect was sufficient. Conclusion Growing on rock wool seems to become a useful alternative in carnation growing. While soil desinfection in diseased houses claims raised benches to be effective, benches can be spared, where plast covering and rock wool is used. Furthermore the slabs are clean and easy to handle. Easy water uptake and possibilities for a fine nutrition controle are other advantages. However, the feeding programme and correct water controle is essential for satisfying results, and a running ph and conductivity controle is necessary. Rock wool growing is not an easy solution of problems, and no compensation for poor growing, but if the system is intelligently used and carefully handled, it may lead to raised production and even a better quality than growing in soil. References Bagge Olsen, O., 1970. Stenuld som dyrkningssubstrat (Rock wool as growing medium). Gartner Tidende 86:115-116. Hansen, M, 1976. Potteplanter s naer i ng sop tage 1 se. (Nutrient uptake in pot plants). Gartner Tidende 92:158-160. Hornum For sfagss ta t ion, 1971. Stenuld som s t ikke subs tr a t. (Rock wool as rooting medium). Statens Fors0gsvirksomhed i PI antekultur. 985. meddelelse. Hornum Fors0gsstation, 1971. Granuleret stenuld som dyrknings substrat. (Granulated rock wool as a growing medium. Statens Fors0gsvirksomhed i Plantekultur. 992. meddelelse. Mosegaard, J., 1970. Fra det ukendte. (Concerning rock wool growing). Gartner Tidende 86:664. Nielsen, N.E., 1976. Om formulering af naer ings s to f op\<b sn inge r (On formulation of nutrient solutions). Tidsskrift. Planteavl. 80(2) : 175-180. Willumsen, J., 1971. Vandre tension, vandbe vaege 1 se og iltdif- 218
fusion i inaktive rodmedier. (Waterretension, Water Movement and Oxygen Diffusion in Inert Root Media). Tidsskr. Planteavl 76(4): 570-580. Figure 1 Figure 3 219