Misting Systems for the Greenhouse

Greenhouse production at commercial nurseries requires a heavy investment in both time and money requiring a high yield of good quality plants to justify the effort. As a result, many techniques open to the professional grower are simply too expensive for the hobbyist. However, misting systems are one exception to this general rule and a range of automatic units are available, making all the advantages of this method of plant propagation possible in the home greenhouse.

How it Works

The idea of intermittent misting first arose in the 1950s, principally to root softwood and semi-ripe stem cuttings – allowing up to six batches to be grown-on a year and enabling many types of plants that used to be grafted, to be rooted at considerably less cost.

The principle behind it is very simple – fine droplets of water are intermittently sprayed over the plants being propagated, moistening and cooling the top surfaces of their leaves and providing all of the water that they need. The idea is to make sure that the thin film of water keeps the foliage in good condition and stops it from drying out. Some types of systems also have a heated base which helps to promote root development. While seeds and seedlings do well in a misting system, leafy cuttings seem particularly suited to being propagated in this way and will generally form roots far more rapidly, in larger numbers and with more certainty than under more conventional methods of husbandry.

Of course, using misting systems is not entirely trouble-free and it is important to pay attention to one or two aspects in particular to make sure you get the best out of this approach to raising plants. Draughts need to be minimised to avoid disturbing mist distribution – the units are usually open – and it is clearly essential to make sure that the misting heads are all working properly.

Some kinds of nozzles – notably brass – are prone to clogging if the mains water is hard and this can also lead to mineral deposits being left on the leaves of slow rooting plants. If hard water is a problem, it may be worth investing in some method of softening it or alternatively running the misting unit from a pumped and filtered rainwater supply. In addition, since mist propagation covers the surface of the plant with fine droplets of water, it may not be suitable for plants which are known to be particularly at risk from rot. However, there is some evidence to suggest that fungal spores can be washed out of the air and off the leaves before they have a chance to infect the plants being misted.

Systems Available

The options available range from small, portable misting sticks costing around £15 or £20, up to dedicated units with soil heating cables and thermostats for £400 or more and it is also possible to build your own system.

Dedicated units offer a complete propagating bench with sophisticated soil warming systems to provide the necessary warmth to the roots to encourage their quick development and are usually controlled by an “electronic leaf”. This is a clever piece of electronics in a plastic box, which is placed amongst the plants to monitor the amount of water they receive – automatically regulating the process and providing frequent fine misting to ensure moisture and humidity levels are maintained. This inevitably guards against both scorching and wilting, contributing significantly to the success rate of the system, even with plants which would normally be considered difficult to propagate.

If the costs of a dedicated unit cannot be justified for the number of cuttings you want to produce, it is still possible to dabble in the technique, without spending too much money. While they may not offer the same level of control or sophistication as the larger systems, misting kits and portable sticks offer low cost options which are ideal for small scale propagation. They can also be coupled with an electronic leaf – although this does add significant additional cost – if a greater degree of precision is wanted.

One of the key advantages of misting is that with the ability to control the humidity and growing environment, the propagation of valuable or “difficult” plants becomes considerably easier, allowing you, in your own small way, to play the big boys at their own game. Instead of buying them in, you can have the satisfaction of having raised them yourself – and at a fraction of the cost!

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