Water Management

Watering on stone wool substrate: caution advised!

Jan van Staalduinen

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!"

GroSens, grodan

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

grodan, blog, huub
Sustainable Growing

A peek behind the scenes at Grodan

Have you ever wondered what happens behind the scenes to ensure that you receive the Grodan products you’ve ordered? Find out by reading a series of interviews with some of the people involved! In this edition, we spoke to Huub Hermus, Key Account Manager Vegetables for the west of the Netherlands.

Read more
Grodan, shoot, e-gro, Gursel Karacor

Why Crop Registration Matters – e-Gro customer case video’s

Crop registration is a key activity in your greenhouse in order to know how your crops are growing, based on this information you can set better your growing strategy and adjust whenever it’s needed. Watch the video’s below to discover more about why crop registration matters and how it’s applied in practice at the Dutch tomato greenhouse company ‘Van Rens’.

Read more
grodan, blog
Sustainable Growing

Grodan experiments with recycled plastic in foils: 'Quality is guaranteed.'

Grodan has been working on various recycling trials for several years, an important step when it comes to sustainability. What are the benefits for growers when we use recycled materials in our products, how exactly does it work, and what is involved? Susanne Ruthenberg, Grodan International Product Quality Manager, clarifies these questions in this interview.

Read more
Grodan beauty of horticulture series
Sustainable Growing

Searching for resilient root zones that can take a hit

Organizations and academics in greenhouse horticulture are continuously looking for new and innovative ways to combat new and existing plant diseases in a natural way. Grodan, led by Peter Spoor, Director of Applications & Development, is currently involved in national and international research initiatives to better understand the role and function of microorganisms in substrates. In this interview, Spoor explains why these studies are so relevant to the sector. “By stimulating and directing microbiological life in the right direction, the plant becomes more resilient and can therefore fight pathogens more easily.”

Read more