Greater re-use of drainage water for pot orchids is one step closer with a new compound fertiliser. Phalaenopsis grower De Molenhoek in Bemmel, the Netherlands, has been using this strategy for the past year and a half and it is allowing them to gradually increase the amount of water they recirculate. “We started with the cooling and flowering phases and moved on to the vegetative phase later. We are building up gradually because we don’t want quality to suffer. Our ultimate aim is zero discharge,” Otto Basten explains.

The fact that restrictions on discharges into surface water are becoming ever tighter is old news. Since 2015, emission standards have required pot orchid growers to limit discharges to no more than 200 kg N/ha/year. This will drop to 150 kg/ha/year in 2018 and to almost zero by 2027.
Growers Otto Basten and Marcel Arts are pleased they anticipated future regulations when they built their new facility. Basten: “The floors are in a V-shape with a gutter, so we can collect all the drainage water in four retention basins.”

Centralised facilities

Basten and Arts moved to Bergerden, a greenhouse horticulture area in Lingewaard in the east of the Netherlands, eight years ago. They had run out of options to upgrade their old premises in Horssen, which the partners had taken over from their former employer in 2004. So they relocated to a 1.6 ha site at their present location in 2008, adding a further 1.5 ha in 2011. They grow about 100 species of Phalaenopsis, with 20 main species. The two, three and four spike plants go to florists and retail outlets via direct sales and auctions all year round.
A big advantage of the cluster in Bergerden is that there are centralised facilities there. The CHP plant delivers heat, electricity and CO2. Thanks to the communal rainwater harvesting system, there is always plenty of irrigation water. Basten: “We have two types of ditches: one for clean water and one for wastewater. We collect the water from the greenhouses and it passes along the clean ditches into the central rainwater harvesting system. This has enough capacity for twice the number of horticultural businesses we have here at the moment.”

Adding more depending on EC

So there’s plenty of clean water. And yet the growers are very keen to keep on increasing the amount of water they recirculate. Once they have collected the drainage water in the retention basins, they first treat it with the UV disinfection unit. Then the treated water goes into a separate silo. Depending on the EC, they then mix in water from the clean water silo and new fertilisers.
“We are building up more and more knowledge about watering and recirculation. It wasn’t until we started using these retention basins that we noticed how much water was coming back into them. So we became a lot more aware of how much we were watering. Having started out using a very loose, coarse bark substrate, we later switched to a more compact, finer one that retains the water and the minerals better. That alone reduces the amount of drainage water quite significantly. And because we are using Reci fertiliser, we can keep re-using the water for longer,” Basten explains.


The compound fertiliser Plant-Prod Reci from Horticoop plays an important role in recirculation. The growers have been using this for the past year and a half. Adviser Leo Hoogeveen from the supplier introduced them to it. He explains that this fertiliser was specially developed for orchid cultivation in collaboration with Canadian manufacturers Plant-Prod in 2013. As the name suggests, it is specifically designed to enable targeted recirculation. The adviser explains how it works.
“The purpose of this product is to enable growers to fertilise as cleanly as possible, with minimal ‘background noise’. First of all, it is low in sodium. Many fertilisers contain too much sodium and it accumulates when the water is recirculated. The plant doesn’t absorb it, so more and more sodium ends up in the system. That inhibits plant growth. Removing the sodium enables water to be recirculated for longer.”
Just like sodium, too much sulphate is also a problem when re-using water in plant cultivation. So this fertiliser contains no sulphate but has added magnesium instead.

Stabilised polyphosphate

The fertiliser also boosts plant strength and the root system, Hoogeveen says. “To achieve that, we have replaced most of the phosphates with polyphosphates, which are available to the plant for longer. This has the advantage of strengthening the root system. Also, they are already stabilised, which they wouldn’t be if they were given separately. The pH of separate polyphosphates is too high, so the grower has to acidify the fertiliser himself to neutralise it. Our compound fertiliser works more easily and prevents mistakes. Polyphosphates have the added advantage that they remove inorganic contamination from the system.”
Another feature of the compound fertiliser is that it doesn’t contain a trace of boron, copper or zinc. Many other fertilisers contain low levels of these as standard. “Phalaenopsis growers don’t generally need these elements; they are just dead weight. Levels of boron, copper and zinc are often ‘low’, but in this case it’s ‘no’.”

Correct use

It all sounds good in theory, but how are they finding this fertiliser in practice? Basten is positive, although he immediately adds that every grower will use it differently and that it seems to work better for some species than for others. “The trick is to find out in your own operation how best to use it to increase recirculation. We have stepped up our re-use gradually so as to avoid making mistakes. The percentage in the cooling and flowering phase was already high, but we have always been very cautious in the vegetative phase. That’s the most vulnerable period because the temperature is high and diseases can easily develop. Since we started using the new fertiliser, we have been able to recirculate in this phase too.”

Quality unaffected

So far the strategy has had no negative effects. The quality of the plants is exactly the same as before, Basten says. According to Hoogeveen the fertiliser may even help improve quality, although Basten doesn’t feel he can comment on this. For him, it’s a question of slowly gaining the confidence to increase recirculation.
“You can’t help worrying about spreading diseases via the water. Naturally, we remove any affected plants every week and all the water passes through the UV disinfection unit, but starting off ‘clean’ feels better. That’s why we are doing it in small steps. At the moment we are still discharging twenty per cent of our drainage water.”

Full recirculation

Basten has discovered that he can recirculate more than he first thought. “Everything we need is in the fertiliser in the right proportions. In the past, sodium and zinc levels could easily get too high. Now our drainage water has lower levels of unwanted elements than before. We can see that from the samples.”
Basten thinks full recirculation should be achievable in the future. Of course, a Phalaenopsis grower will need to have the right facilities in place. He also assumes that suppliers’ knowledge levels will continue to develop. “We will be able to do more and more with new products like this and with other substrates too. I’m sure of that.”


Phalaenopsis growers De Molenhoek have been able to increase the amount of water they recirculate by switching to a new compound fertiliser. Because the fertiliser contains very few if any unwanted elements such as boron, copper, zinc and sodium, they can re-use their drainage water for longer.

Text: Karin van Hoogstraten. Image: Gert Janssen (Vidiphoto)