Passive grow systems

Passive grow systems are nothing new

Passive grow systems are nothing new, but we are coming across them more and more frequently. These systems do not need any electricity to operate but water the plants exactly as they require and in addition they work silently. Are they as perfect as this list of positives makes them seem? Let’s have a closer look at passive systems.

I first read about passive systems many years ago in a book on hydroponics. One end of a ribbon (wick) leads into the planter, and the other end is dipped in water. On the one hand, the wick takes in water, which on the other is soaked up by the soil from which the plant then absorbs the water it needs. How simple. The soil takes in only as much water as is needed and there is no danger of overwatering. The water tank is usually situated lower than the planters, or at most at the same level, and the distance between tank and planters is not great. If the tank was elevated above the planters, the wick would draw down more water than is needed. So the only prerequisite for a correctly functioning system would seem to be the correct choice of materials. The wick was invented a long time ago, so no problem there. However, if you try to replace the wick with an ordinary piece of thin fabric, you must of course prepare yourself for difficulties which usually lead to the system not functioning. The wick system is still used, for all sorts of planters and plants. In any hobby market or garden centre you can buy an elongated planter, usually placed on windowsills in the home, for geraniums, pelargoniums and other plants, which are equipped with wick systems.

Although passive grow systems existed long before cultivation under artificial lighting became widespread, you will search in vain for them in growers’ grow rooms. Among indoor cultivators the wick system is the exception, not the rule. Another type of passive irrigation system is gravity-fed irrigation. A water tank is positioned above the irrigated plants and gravity pulls the water down through a narrow capillary. It must drip and not flow. It is necessary to be careful and keep a close eye on this system, to ensure that the quantity of water dripping through the capillary is not too large. If you don’t have a container with a small air hole at the top, only some of the water will run out of the container and the dripping will then stop. In this way it is possible to set up a system which allows only some of the irrigation solution to flow out every day. Everything must be carefully measured and tested. Not only the size of the air hole, but also the size of the container and the strength of its walls all have a role to play. If, for example, you used an ordinary 5-litre bottle made of PET, the plastic may deform as a result of the vacuum created by the water as it runs out. The result can only be that more water flows down to the plants than you wanted, and it will end up overflowing the planters or the trays beneath them. The disadvantage of a home-made passive gravity-fed system, as is probably obvious from the previous lines, is the difficulty in setting the dose of the irrigation solution. The wick system mentioned right at the beginning will also respond much more accurately to the needs of the plants. This means that the moisture levels in the growing medium will be constant, whether the plant needs less water, or more. If you are cultivating several plants and using the wick system, each plant will get only as much water as it needs. Thus two plants, which have different needs, will each get the amount they need, even if one needs 100ml per day and the second 500ml per day. An amateur gravity-fed irrigation system will not achieve this effect. You would have to make a valve connected to a float. Maybe some of you can do this, but I unfortunately could not.

In recent years the ever greater desire among cultivators to save energy has become more obvious. Growers try to save money on power for lights, fans and of course irrigation. This trend has created the opportunity to polish up the old wick technology. If you have ever had a look around a horticultural trade fair, you will certainly have noticed modern-looking passive systems. However you don’t need to go anywhere. Online and in internet stores you will find relatively new sections with the name passive irrigation systems. I must now mention the name of one manufacturer, because I think he has awakened interest in passive irrigation not just in people who did not have the first notion of it, but also in those who knew about it but considered it too complicated to install in their own growrooms. This man is Paul Cronk, but maybe you will better know the brand AutoPot, which is in many countries a synonym for passive systems. What was it that Paul did differently, which caused passive systems to increase in popularity so much? He added to wick and gravity-fed irrigation a simple valve with a float, thanks to which it is possible to connect the system for one or dozens of plants and happily go off on holiday, because you know that your plants will get exactly as much watering as they need.

If passive systems have caught your interest, you can find many different types made by various manufacturers on the market. Mostly, however, they revolve round the above-mentioned wick system combined with gravity. This model is equipped with the valve described above, which ultimately you can see in the photos to this article. You will need to equip the system with a tank of nutrient solution of any size and you can use it to irrigate even a large number of plants – without electricity costs, of course. But so that we aren’t praising passive systems forever, we need to look at the other side of the coin and consider the disadvantages of these systems.

The first, and considerable, disadvantage is the cost of passive systems. One planter with a valve will cost you no less than €30, which is not a sum anyone would normally pay for a planter. In general you can say that those €30 are the sum one cultivation unit will cost you, if you intend to grow as many plants as you want. If we compare this outlay with, for example, the Atami Wilma system, where one planter will cost the equivalent of around €15, we can see that the difference is significant. Many of you will now be asking: how quickly will we see a return on such a high investment in a passive system? Of course, it all depends on how many plants you intend to grow. Nevertheless you cannot compare a passive system with an active one purely on the basis of acquisition costs. As already stated, a professional passive system has something which an active system cannot do for that price – it waters the plants when the plants need watering. The optimal result is bigger, healthier plants which give a more abundant harvest, which will soon compensate you for the higher outlay.

The second disadvantage of passive systems is stagnant water. Let me tell you how the valve in modern passive system works. The valve is placed in a small tank which supplies the irrigation for one or several planters via a wick. The tank is supplied with nutrient solution by a pipe leading from the source reservoir to the valve. The valve will open when the tank is full and will allow the pre-set amount of solution to flow in. The valve will open again when all the water in the small tank has been used. The water is in the tank from the moment the valve lets it in until it is all used up. The time this takes can vary. The tank will never dry out, which is a good thing. Nevertheless, I have already witnessed the occurrence of pests in the small tank. Humidity, warmth and darkness create ideal conditions for the proliferation of various organisms. Because the tank is shallow it is more attractive to parasites than the source reservoir of nutrient solution, which is too deep. This problem can be avoided by regular preventive checks on the tank. As soon as you see any unwelcome life-forms, dry out the tank and wipe it by hand, maybe with a little alcohol, which will quickly evaporate off. Instead of alcohol you can use a suitable insecticide made of natural ingredients.

However much we consider the advantages and disadvantages, we should never forget about passive systems. Personally I am an advocate of watering by hand, but given that I cannot always be with my plants, I prefer an active irrigation system and hydroponics. The passive wick system is, in my opinion, the closest equivalent to watering by hand, and in addition it gives me freedom of movement, so I am not tied to my plants.

You will find passive systems in places other than indoor growrooms. The clever planter which irrigates itself is suitable for use in greenhouses, or outdoors, and you can grow quite large plants in it. If they are outside, and it rains, the irrigation of the planter will not change, because any excess water following a downpour will flow off through the valve and the plant will begin to take up water from the tank when it needs to. And what do you say to passive systems? Are you tempted to give them a try? You could start by making your own using a wick and share the results with us. Even if you haven’t tried this, it doesn’t matter, it is enough that you know about passive systems. Maybe you will find this useful in the future.