Soilless Raspberry Growing in Substrate

What is soilless raspberry growing?

Soilless raspberry is a system where the plant grows in a substrate such as coir (coconut peat), inside a pot or growing bag, rather than directly in field soil. The water and nutrients the plant needs are delivered to the root zone as a nutrient solution through drip lines. Nutrition is thereby taken out of the variable, uncontrollable conditions of the soil and turned into a process the grower can manage.

The method comes into its own on holdings where the soil is unsuitable for raspberry. On heavy clay, saline or high water table land, or where soil-borne disease pressure is high, conventional production in soil can be both risky and low yielding. A substrate system removes most of those limitations.

When does a substrate system make sense?

Moving to a soilless system is not automatically the right decision for every holding. On land that is already well suited, well drained and low in disease pressure, the extra investment may not justify itself easily. In the following situations, however, a substrate system deserves serious assessment:

• The soil is heavy clay, saline or has a high water table.
• The land has a history of soil-borne root diseases (for example Phytophthora).
• You want to manage nutrition and the water regime precisely to raise quality.
• You are targeting higher yield per unit area in a limited space.

In my field work I recommend making the decision on calculation rather than feeling: the yield and quality currently achieved in soil should be weighed against the increase a substrate system would bring and the cost of the investment. The principles in the berry fertilization article apply here too; the difference is that in substrate they can be applied far more precisely.

Which substrate and pot system is used?

The most common substrate is coir (cocopeat) produced from coconut husk, sometimes blended with perlite. Three properties are looked for in a good substrate: sufficient water holding, good aeration, and drainage that lets excess water leave easily. Roots suffocate in an airless, permanently wet medium, so the air-water balance of the substrate is the foundation of root health.

Plants are generally placed in growing bags or pots on raised rows. A raised system both eases drainage and makes harvest and maintenance ergonomic. Pot volume is chosen according to variety and target plant size; adequate root volume matters for preventing water stress in hot periods.

How is the nutrient solution (EC and pH) managed?

The heart of a soilless system is nutrient solution management. Soil acts as a buffer and partly forgives mistakes; in substrate that buffer is weak, so measurement and control are essential. Two basic parameters are tracked:

• EC (electrical conductivity): shows the total salt and nutrient concentration in the solution. Too low an EC leaves feeding inadequate; too high stresses the root and makes water uptake harder.
• pH: determines nutrient availability. A slightly acid range is targeted for raspberry; as pH rises, iron and manganese uptake is disrupted.

In practice the EC and pH of both the solution applied and the drain water leaving the pot are measured regularly. The drain values are the most honest feedback on how the plant is using the solution. Values are adjusted by growth stage: one balance in the vegetative period, a different, potassium-weighted balance during fruit filling.

Why do irrigation and drainage matter so much?

In a substrate system, irrigation is not “one heavy watering a day” but many small irrigations spread through the day. The aim is to keep the substrate continuously moist without leaving it airless, and to produce some drainage (excess water) at each irrigation. That drainage prevents salt building up in the root zone and preserves the nutrient balance.

Irrigation frequency changes with air temperature, plant size and time of day. Demand rises in the hot midday hours and falls at night. In a well-built system, irrigation is managed automatically according to climate and substrate moisture. Collecting and disposing of the drain water, or reusing it, should be planned into the system from the start. To keep the drip lines free of blockages and filters in good condition throughout the season, the drip irrigation maintenance guide is a useful reference.

What should you be ready for in investment and know-how?

Soilless production asks for higher establishment investment and more technical knowledge than conventional soil. Substrate, pots, the drip system, the fertilizer unit and climate management work as one whole; a fault in any of them affects the entire system. Before moving to it, both the investment and the technical capacity of the holding should be assessed realistically.

Because cost and yield vary greatly from holding to holding, it would be wrong to quote a fixed figure here; these must be calculated separately for the region, greenhouse conditions and scale. To size your system correctly and set up the substrate and nutrition program, look at the other guides on the berries hub page, or take consultancy before establishment. A properly built substrate system turns unsuitable soil from an obstacle into a controllable production environment.