Growing a mix of lettuce, lettuce leaves, and young leafy greens

Lettuce heads are losing popularity and are being ousted by green and colorful, loose-leaf mixes. Add to that open-field lettuce and leafy crops being under pressure from climate change, labor shortages, the desire for clean food-safe cultivation, and planned continuous supply.

Then it becomes evident that chain parties are willing to invest in hydroponics. The latest developments in that field were on display in the Netherlands at the Rijk Zwaan Hydroponics Demo Days. These once again attracted enormous interest, says Lettuce crop coordinator Peter Sonneveld.

Peter Sonneveld, Rijk Zwaan's Lettuce crop coördinator.

Growing on water in a greenhouse (hydroponics) lets you mechanize a crop from sowing to harvest and control growing conditions. You do not even need plant protection products. Another advantage is that you can cultivate different lettuces and leafy greens in the desired mix. Though you must do the math versus regular cultivation per situation, this controlled cultivation method is emerging worldwide.

Rijk Zwaan's breeding program entirely focuses on lettuce and leafy varieties that perform well in hydroponics. "It's much more expensive to grow on water, but it's still desirable in large parts of the world because there are fewer risks. Think of crop failures due to climate change or the fear of bacterial contamination, such as E. coli," begins Peter.

"There were recently several outbreaks in America." The entire cultivation process can be fully automated, which partly means this growing method allows for further chain integration. "Growers are increasingly processing their produce on site and investing in packaging lines to market their product directly," says Peter.

Salatrio
You can cultivate lettuce heads, loose-leaf lettuce, and leafy greens on the water in all kinds of combinations. Rijk Zwaan, therefore, continues to develop the Salatrio concept in which three types of lettuce are grown on one taproot. It results in a beautiful colorful product. It also has a long shelf life because the lettuce is harvested and packed with the taproot attached, keeping it alive.

Demand for this is skyrocketing, especially in Europe, Japan, and North America. In breeding lettuce types, it is vital that they grow at the same rate. There are now Salatrio combinations with Salanova® varieties that offer more flavor, crunch, leaf type, and color options and have an increased number of leaves.

The first green Salanova® Gem variety for hydroponics.

A single head provides a handful of tasty, loose, evenly-sized leaves.

Salad mix
Various new varieties that can be cultivated at high densities have been developed, especially for the loose-leaf salad mix market. The large variety of leaf types means the desired salad mix can be produced and harvested mechanically. Such mixes have an extra added value.

They consist of young leafy greens like spinach, arugula, kale, lamb's lettuce, chard, and endive. Here, too, opportunities are arising for hydroponic cultivation. Peter: "Spinach is a very important but hugely challenging crop. By nature, this crop does not like getting its feet wet, but we're making great strides in breeding these varieties."

The new intensely red Crystal variety, Sungari RZ.

The Sungari RZ's red color runs through the leaf, deep into the rib.

Sandwich Range
Lettuce as a garnish is an important segment too. Here Rijk Zwaan already had various lettuce varieties in The Sandwich Range. These have lots of suitably-sized leaves and are heat and acid-resistant. The varieties' shapes and bites vary. A red variety of Crystal Lettuce is a welcome new addition. Its intense red color runs deep into the leaves' ribs.

Rabello RZ, a semi-closed romaine lettuce.

Cut open, Rabello RZ shows that it is exceptionally well-suited to a high-tech hydroponic cultivation environment.

Heads
Rijk Zwaan also sees an opportunity to grow lettuce heads for the processing industry. "The convenience trend keeps growing. Parties with year-round production, especially, want to increase their processes' certainty and efficiency," Peter concludes.