Mist systems used in plant propagation are often poorly designed and managed. Inadequate water pressure, incorrect spacing of the mist lines and nozzles and nozzles spaced too close to the walls of the propagation units, will inhibit the diffusion of the mist across the propagation area. Waterlogging of the rooting medium is the most common problem. Too many droplets which are too large knock down the small mist particles thus reducing atmospheric humidity. This in turn results in faster drying out of the crop which leads to an increased frequency of misting cycles. It is also vital to get the water quality just right. High alkalinity levels can seriously reduce a cutting's ability to form roots. Highly alkaline water will also interfere with the mechanics: blocking the nozzles with scale and causing uneven distribution pattern and limiting the ability of the nozzles to produce a true mist. Filters and metal solenoid valvues should also be cleaned and the lones (tubes) flished out regularly. "The Commercial Greenhouse Grower". Fax: 0044 1622 663733 Green@actpub.co.uk