Every year, somewhere in the world, a berry grower walks away from substrate production convinced that substrate just isn’t for them. It’s too expensive, the plants underperform, the results are worse than in soil. The substrate gets the blame. Almost always, it isn’t the substrate.

The promise, and the gap

The shift from soil to substrate brings real advantages: tighter nutritional control, fewer root disease issues, freedom to choose farm locations regardless of soil quality, and, in crops like raspberry and blackberry, the ability to work with long cane programmes in production windows that soil simply doesn’t allow.

But moving to substrate isn’t just swapping dirt for coco or perlite. It’s a change of mindset, a training exercise for the team, and, more often than not, a full review of the irrigation system. The problem is that many growers carry their soil irrigation habits straight into substrate, get disappointing results, and conclude the system failed them.

The system didn’t fail them. The buffer did.

In soil, you have a large, forgiving reservoir. Water, nutrients, and, crucially, mistakes, get absorbed and diluted across a large volume. Substrate, particularly in smaller pots, offers no such luxury. Every irrigation decision matters. There is no hiding place.

So why do we drain?

Plants absorb water and nutrients, but not all elements in equal proportion. Over time, compounds the plant uses less, sodium being the most common offender, accumulate in the substrate. Without regular drainage to flush them out, their concentration rises, EC climbs, osmotic pressure increases, and the plant starts struggling to absorb water even when there is plenty available. You end up with a stressed plant sitting in a wet pot. It is as uncomfortable as it sounds.

The plain water flush. A tool, not a strategy.

The starting point is simple: measure the electrical conductivity of the water arriving at the plant (the drip, or “in”) and the water leaving the substrate (the drain, or “out”). Daily, ideally multiple times a day during critical periods. When drain EC rises, most growers know something needs to change. Where things get interesting is in what they do next.

The most common response to rising drain EC is to irrigate with plain water, cutting fertiliser for part of the day or for several days, to flush the substrate. This can be appropriate, but only as a short-term measure, and only when everything else is already under control. Used blindly, or for extended periods, it creates something arguably worse than high EC: oscillation.

Plants under substrate cultivation depend on a consistent supply of water and nutrients. Cutting fertiliser for days at a time is the horticultural equivalent of putting a child on a water-only diet until their weight stabilises. The number might improve temporarily. The child will not.

Before reaching for the plain water lever, there are questions worth asking. Are you using the right fertiliser programme and EC level for the variety, the climate, and the current growth stage? Is drainage occurring uniformly throughout the day, or does it stop during the hottest hours when evapotranspiration peaks? Is your source water actually suitable for berry production, and if sodium is a recurring issue, is reverse osmosis worth the investment?

Plain water flushes treat the symptom. These questions look for the cause.

Draining too little: the short-term saving and the real cost

Draining less does save water and fertiliser in the short term. That part is true. The question is what it costs you elsewhere.

Some growers also reduce drainage deliberately, hoping higher substrate EC will improve fruit consistency. It can help, but only if the reason fruit quality is suffering is actually excess water. If the plant needs less water, irrigate less. On days with high humidity and low evapotranspiration, your irrigation requirements may drop significantly, sometimes to zero. Reducing drainage is not the same thing as addressing the root cause.

And when drainage drops for the wrong reasons, EC in the substrate rises, elements accumulate, and nitrates are a good example of what builds up. The plant will absorb them. More nitrate uptake tends to mean softer fruit, which is the opposite of what most growers were trying to achieve in the first place.

The other side of this fear of draining is a confusion between daily drainage percentage and overnight substrate moisture. Running at 30 to 35% daily drainage does not mean your substrate will be waterlogged at night. If you time your last irrigation correctly and allow the plant’s end-of-day water consumption to bring moisture content down naturally, your overnight substrate conditions can be perfectly healthy. The percentage tells you what left the pot. It doesn’t tell you what stayed in it.

Drain when the crop needs it. Not 50% throughout the season, not out of habit, but not out of fear either.

Drip and drain analysis: still a rarity, shouldn’t be

Measuring EC is the baseline. Understanding what is actually in that water requires analysis.

There are three points that tell the full story. What arrives at the plant: is it what you planned, or has there been a dosing error, a tank mixing issue, or fertiliser precipitation in your stock tanks affecting what actually reaches the dripper? What is in the pot: what is the plant actually experiencing day to day? What is draining: what is leaving the system in excess, and should that prompt a change to your base recipe?

Regular drip and drain analysis is still rare in most berry operations. It shouldn’t be. It is one of the most direct windows into what is actually happening at root level, and in substrate production, the root zone is where everything is decided.

Final thought

Substrate production is not harder than soil production. But it is less forgiving of inattention. Drainage is not a problem to minimise, nor a tap to leave running. It is a management tool, and learning to use it properly is one of the clearest separators between operations that make substrate work and those that conclude, wrongly, that it doesn’t.