soiless leafy salads

The production of crops without soil, typically through hydroponics, using nutrient-enriched solutions with or without growing media, offers a unique opportunity for the Welsh horticulture sector. These systems are particularly beneficial when producing leafy crops such as leafy salads which can be grown at high densities and achieve higher marketable yields compared with similar crops grown in soil.

The market has diversified, with consumers seeking a varied diet of multi-leaf salad mixes including microleaf lettuce, watercress and pea shoots. Mixes including coloured leaves such as amaranth and chard, or flavourings including baby celery leaf and herbs, are in particular demand in the food service industry. The UK prepared leaf salad market grew by 6.6% in 2017 to almost £700 million buoyed by continuing consumer demand for fresh, nutritious produce that aligns with emerging “superfood” trends. Seasonal demand peaks in the summer, but continued demand from restaurants throughout the year can ensure a market for as long as the salad can be grown.

Welsh locally grown leafy salads present an excellent product development opportunity for horticulture: it is a short growth cycle, high value product which shows rapid drops in flavour and quality in extended supply chains. By increasing the availability of locally-grown, high quality salads, growers will be able to exploit the increasing consumer demand and increase the profitability of their growing enterprise.

Salads also align with the long-term vision of the Welsh Government for horticulture, by diversification from traditional horticulture soil grown crops. New leafy salad crop selections, which are well suited to soilless growing systems will add value to a regional supply chain – Welsh-grown salads would offer sound investment potential for Welsh-made food and drink products, marketed directly to consumers.

Leafy salads are well suited to hydroponics and can be developed as a new business or an extension of an existing business. Salads can be grown in a range of glasshouse or polytunnel structures. Salad leaf crops can be grown at high densities with shorter growing times, achieving 3 – 4.5 kg/m2 compared with yields of 2.5 – 3 kg/m2 for field grown lettuce. This approach also minimises pest/disease risk, such as Pythium which can persist in the soil between crop rotation. Weed control is also much easier as there is little space in the production system for weeds; weed control can be particularly problematic for herbicide-sensitive rocket, when grown in the field.

As salad is eaten raw, the ability to grow a crop in the absence of soil minimises the risk of contamination enhancing marketability of a clean crop. High planting densities also increase the efficacy of biological controls for pests and disease management in the root and shoot zones. Labour costs can be reduced by stacked or table-height production compared with crops grown in the ground in a single layer.

The ability to control the growing environment means that optimum resource efficiency can be achieved while offering a highly uniform and consistent product that has the potential to be grown year-round. The recirculation of water and nutrients means that water wastage is 20 times less than that typically seen in soil grown systems, which is an important environmental protection measure for sustainable food production.

While soilless cultivation methods can be started at a relatively small scale using basic technology, it can be readily integrated with innovative growing technology such as light-emitting diode (LED) lighting to greatly increase output and production efficiency from the growing area.

This document has been written as a practical guide for growers who are seeking to diversify their business using hydroponic techniques.