A what? It is a propagator with a difference and the idea comes from hydroponics, a form of soilless culture using circulated water with added nutrients percolating through a neutral substrate in which the plants are growing.  Typically these have been pretty large commercial installations, though I have seen a smaller scale private system in which, among other plants, orchids were growing remarkably successfully.  Over the years I have been intrigued by the theory but never found an opportunity to put it into practice – until I noticed an item in one of the usual greenhouse and horticultural bits and pieces catalogues. The idea had immediate appeal and, sucker that I am, I bought one.

The Hydroprop consists of a black plastic tank filled with water warmed by an adjustable aquarium heater and containing a small pump and an array of spray nozzles at surface level projecting water nearly horizontally so that it plays on the underside of a tray containing foam discs with a central slot, cut to the outer perimeter to allow plant cuttings to be inserted with the base of the stem projecting into the constant spray from the nozzles.  The whole thing is surmounted by a transparent plastic dome with two adjustable ventilators.  The foam discs can be washed and reused, but are easily replaceable when they get past it.  Nutrients are also available as an option depending on how long you want to leave the plant material in the propagator.  I prefer to use just clean water and pot the cuttings on as soon as they show enough of a viable root system.

Wonderful! But does it work?  Well, yes it does and for some plants it seems especially beneficial.  In the accompanying pictures three quite different sorts of cuttings are shown at the point they have been removed from the Hydroprop to be potted on into standard potting compost.  Xerochrysum (a tender perennial relative of the Helichrysum well known to many as an annual everlasting flower) and Argyranthemum seem to love the humid conditions and root strongly in 10 to 14 days.  Unsurprisingly Impatiens, which are often rooted in a jam jar on the kitchen windowsill, also do very well.  This particularly helpful for I. bicaudata which can be tricky to overwinter as adult plants or even cuttings rooted in conventional rooting medium.  Even sad looking tips of stems that look as though the plant is about to die, root well even in December thereby providing assurance of a good stock of plants for the following Spring.  More surprisingly Erisymum, which tend to be rather woody, have succeeded and Chrysanthemums are easy and reliable.

What about the downside though?  Unsurprisingly absolute cleanliness is paramount.  Broken or fading leaves are prone to fungal infection, flourishing in the warm humidity and romping through the confined space.  Don’t be put off.  This is easily prevented with frequent, preferably daily, monitoring.  And for cuttings with relatively large/soft leaves eg Xerochrysum it pays to reduce the length of lower leaves at the cutting stage to reduce the amount contact between neighbouring plants to maximise air space and reduce the risk of fungal infection.

Whilst checking your cuttings don’t forget to gently lift the edge of the tray (not too much, or you’ll get gently sprayed!) to check the water level inside.  It will need topping up from time to time. It is also worth checking the suckers that hold the heater and the pump assembly in place.  They sometimes come adrift.  The sponge filter on the pump intake also needs to be taken off and rinsed in clean water from time to time.  It is surprising how much muck the filter intercepts.

The positioning of the unit may be determined by the proximity of (damp proof!) electrical sockets. Mine is on greenhouse staging and I need to cover it with shading when the weather is warm and sunny, otherwise the cuttings can flag and take a while to recover.  I also like to leave the vents in the plastic dome open to maximise air flow, and on a daily basis I tilt the dome to one side to allow all the condensed water to drain back into the reservoir.  This prevents it dripping onto the leaves and setting up the fungal problem referred to above.

I’m ambivalent about using the nutrient option mainly because it would be very unusual to fill all 40 slots (a much bigger version is also available!) with the same sort of cuttings and to leave them long enough to require nutrient before potting them on into conventional compost.  For this reason there is a sequence of different sorts being taken out at about the stage shown in the picture and replaced with further cuttings of whatever sort are wanted and happen to be ready to take.

When potting on it is worth remembering that the dramatic change of environment will be a shock to the plant and it needs a bit of TLC to adapt.  I put mine in an ordinary propagating frame with a bit of bottom heat and shading for a week or so until the plant tells me it is feeling comfortable and ready to come out into the real world. In terms of vigour and subsequent growth I fancy the Hydroprop gives the plants a little bit of an edge over conventional propagation, but remember it will not suit some types of cutting and you’ll need to experiment to establish which ones are most worth propagating by this method.  I haven’t tried yet but I wouldn’t rate the chances of success with pelargoniums for example.  So I still use the usual method with sharply drained cutting compost – but I wouldn’t now want to be without my Hydropod. Despite the seemingly finnicky details I mention above it is really quite easy to use and maintain and the care and attention is worth the results it produces.

Roy Stickland