Water Management

Watering on stone wool substrate: caution advised!

Jan van Staalduinen
January 1, 1

Efficiently watering crops grown on stone wool substrate is closely linked to the specific crop growth stage, the desired plant balance, the growth conditions and the outdoor climate (evaporation). Grodan's Gert-Jan Goes mentions some aspects that are currently important to focus on. “The weather is still relatively sombre, but when the sun does break through, caution is advised!"

Pre-drainage and piercing drain holes
Pre-drainage at the start of the growing cycle is becoming more widespread, which is a positive sign according to Goes. Pre-draining involves piercing a hole two thirds of the way up the slab, so the water content (WC) in the upper part of the slab can drop slightly. The final drain hole is made after rooting in, and no later than when the sides of the first slabs feel dry, draining sooner is always possible.

Lowering WC
Lowering the water content while the roots are growing though the entire volume of the slab until the third truss starts to bloom with tomatoes, the first fruit set with sweet peppers, the first heart fruit appears with aubergines or flowering or growth of the first cucumber has now become part of standard growing practice. During this period, little or no water is drained. It is advisable to withhold watering for one or two days during periods of overcast, vegetative conditions.
This strategy results in less to practically no drain effect during the first weeks of growing. Gradually lowering the WC of the slab stimulates the roots to colonise the entire substrate volume with a finely branched root system throughout the slab. The more drip irrigation is applied at this stage, the more roots will form at the base of the slab where the water content is high. A concentration of roots at the base of the slab can cause problems when lots of water is given during periods of high temperatures in summer. This can create anaerobic conditions which kill the roots. Well distributed, finely branched root systems are less easily affected

Different strategy on sunny days
The experiences of growers with restricted irrigation in the initial stage of growing are positive. Especially now, after a long period of overcast conditions, it is however important to follow a different strategy on sunny days and drain well so the water in the slab can be refreshed and to lower the slab EC and pH, as high pH values make it difficult for the plants to absorb various nutrients.

On sunny days, a small volume of water is still being applied via drip irrigation compared with the slab volume. Draining 50% of the equivalent of a coffee cup of water is still very little. A noticeable effect on refreshing the water and lowering the slab EC and pH will only be seen when 1-1.5 litres of water per m2 is drained. The primary goal now is not lowering the slab EC, but efficient refreshment of water instead. Reducing the EC is only necessary when ventilation in the greenhouse is increased and the crop's evaporation capacity has to be boosted.

So the advice is to take things slow and steady in vegetative (overcast, rainy) conditions to encourage healthy root development, but to take well thought out and decisive action on sunny days.

Start early
If you can, or have to, drain a considerable quantity of water on a sunny day, start irrigation on time in large - or larger- drip sessions so the slabs reach the resaturation point quickly. Irrigating using more water also encourages moisture intake and evaporation, which means the drainage moment will often be reached later than expected. Starting irrigation on time with large sessions will start the drain moment sooner so that growers quickly gain insight into the actual drain volume. This strategy means you can still stop irrigating early in the afternoon if the drain moment hasn’t yet been reached and you have missed the window of opportunity to significantly refresh the ‘old’ water in the slab.

Extra caution is also required when the vents open at higher outside temperatures. The evaporation rate of the crop may quickly increase unexpectedly, due to higher moisture exchange with the outside air. Adjusting the radiation sum (smaller initial session) is then necessary to increase the frequency of drip irrigation.

(C) Greenhouse Horticulture Waterproof - Author: Jan van Staalduinen


Latest blogs

water properties, 7 strenghts, waterfall, rocks
Water Management
Sustainable Growing

World Water Day 2023

This year, the focus of the United Nations observance is how to accelerate the change needed to solve the water and sanitation crisis. The global campaign is called “Be the change”. The aim is to encourage society to take action and change the way we use, consume and manage water. As Grodan, being an active member in this society, our aim is to provide the best solutions and provide high-end services that can support growers to “Grow more, with less” and change towards a sustainable way of growing while respecting natural resources.

Read more
challenge, recycling, horticulture, circular economy, Yianni Monahan, interview, grodan
By Yianni Monahan
Sustainable Growing

Is Stone Wool Recyclable? Yes! How Grodan and Walker Environmental Solved a Waste Management Challenge

Solving agricultural recycling challenges: Learn how post-harvest Grodan stone wool substrate is turned into clean growing media for better agricultural waste management.

Read more
Grodan, egro, release update

e-Gro: Optimized Yield Forecaster, advanced crop registrations for more insights and an improved user experience

Being part of the greenhouse sector, we are well aware of the fact that the current season came with multiple challenges and uncertainties in your greenhouse. Gas, energy, the significantly increased inflation, and the changing climate asks for even more flexibility and creativity to adapt to this changing environment.

Read more
Grodan, e-Gro, Grodan101, MJ

e-Gro Q2 2022 release: Better growing with the launch of Crop Analytics, support centre and pepper crop optimizations

We know many of you are facing a number of challenges in your greenhouse. With harvest season right around the corner, you could likely use some extra hands! Unfortunately, with the current staff shortages, extra labor is not easy to find. Additionally, gas prices are higher than ever which makes it even more important to use your energy as efficiently as possible. At the same time, consumers are increasingly demanding high quality crops with sustainability playing an increasingly important role.

Read more