A Delicacy From the Dark: Hydroponic Forcing of Witloof
Belgian endive, also known as witloof, is unlike any other vegetable grown hydroponically and its unique value and sophisticated flavor are two reasons why it is gaining popularity in the gourmet vegetable market.
Ever wondered what those creamy white leaves were in your gourmet salad? Or the bullet-shaped, leafy, pale vegetable grilled and served at a fancy restaurant? Chances are these pale delicacies are Belgian endive (Cichorium endiva), also known as witloof, which, despite its name, is actually a type of chicory—something we are more familiar with as a leafy salad green.
Belgian endive goes by many names depending on where it is being sold. These include French endive, white endive, Dutch endive and witloof chicory. While this is a relatively little known crop in the United States, it has a long history of cultivation in Europe where it has been produced and valued as a delicacy since the 1800s. Witloof is unlike any other vegetable we grow hydroponically and its unique value and sophisticated flavor are gaining popularity within gourmet vegetable markets.
What makes witloof such a fascinating crop is that it has two stages of production. The first takes place as with other salad greens, growing the chicory plants through to maturity. Under commercial production, this is done out in the field from spring to fall. This particular type of chicory develops a large tap root, similar to a thickened parsnip that is cut, harvested, washed and placed into refrigerated storage until it is required for hydroponic forcing.
The second stage involves stacking the bare, clean chicory roots into hydroponic trays, through which nutrient solution flows. This process takes place entirely in the dark so that the shoots that form on the roots are blanched white in colour. The white buds (called chicons) are harvested at a certain stages, depending on market size requirements, and packaged into cartons to maintain complete darkness. Any light during the growing or shipping process will result in the chicons developing green pigmentation, making them unmarketable.
Witloof history and uses
Blanched witloof is a crop that was discovered by accident. In the 1800s, a farmer in Belgium discovered the chicory roots he was storing in his dark cellar over winter to be ground into a coffee substitute, sprouted pale buds with creamy colored leaves and a delicate flavor. Early on, long before the development of hydroponic methods, the witloof roots were forced using a soil or sand medium piled over the top of the harvested and trimmed tap roots.
The sand excluded light so the chicons formed in darkness. At harvest this had to be scraped back, and the resulting witloof carefully washed. Hydroponic forcing eliminates the need to cover the roots with any granular substrate, so the process of chicon formation can be easily viewed and the resulting buds are free from any grit contamination and don’t require washing. The additional nutrition provided from a well-balanced hydroponic nutrient solution also assists with flavor, quality and prolonged shelf life of the harvested chicons.
Witloof flavor is unique and highly valued in a range of different dishes. While green leafy endive and chicory foliage typically has a bitterness that some find unpleasant, the blanched chicons lack any strong flavors and are described as mild, but distinctive, tangy, tender and unique.
Generally, the whiter the witloof is, the milder the flavor. Used as a raw vegetable, the small inner leaves can be added to baby leaf salads and larger leaves are used as elegant wrappers for fillings of crab, caviar, tuna or shrimp, or served with a range of dips. Witloof is also served cooked in a wide range of dishes, including soups, and a simple entrée can be created by cutting the chicon directly down the middle lengthwise, brushing with olive oil, grilling until tender and serving with lemon or vinaigrette.
Hydroponic witloof: first stage
While large-scale, commercial production of witloof roots for forcing typically takes place outdoors, the plant can easily be grown hydroponically during both the first and second stages of production. Witloof chicory grows in much the same way as the endive and chicory plants commonly grown as salad crops. A deep-bed hydroponic system is required to ensure the large, thickened roots can develop without restriction. Suitable growing mediums are fine-grade coco fiber, perlite/vermiculite mixes, granulated rockwool and similar substrates in a growing bed or container at least 1.5-ft. deep.
Whitloof chicory is grown from seed that can be obtained from many vegetable seed suppliers. Suitable varieties are Zoom, Flas’ and Totem F1. Seed is sown directly where the plants are to grow as transplanting can damage the young tap root system. Seedlings need to be thinned to 4 to 5-in. apart when large enough to do so. This is an important step as overcrowding of the plants will reduce the size of tap root that develops, which in turn reduces the yield and quality of chicons that develop during the later forcing stage.
Witloof plants can be given a standard grow hydroponic nutrient formulation during the first few weeks of development, followed by a bloom formulation or P/K booster as the tap root starts to develop. Ideal day length is 12 to 16 hours with moderate temperature conditions needed to produce the highest quality root system (55 to 77°F).
These conditions replicate the outdoor conditions received by the plants, which are typically sown in spring. Tap root production usually takes around 110 days, but this may be sped up under the controlled conditions of an indoor garden. Harvesting of the chicory roots can take place as soon as they are mature and of a sufficient size.
Maturity can be determined by examining a vertical-cut section of the root, just below the plant crown. Mature roots will have a white section, approximately a quarter-inch thick in this region. If the white region is smaller than this, the root is not mature enough for later hydroponic forcing. The best quality roots will be 1.5 to 2 in. in diameter at this stage.
At harvest, the green tops are cut from the plant to remove as much foliage as possible without harming the growing buds at the top of the tap root. The root system can then be removed from the growing substrate and lifted, with any loose media brushed off. In preparation for storage, the roots can then be washed.
They may also be treated with fungicide to help prevent rotting if they are to be kept for several months before forcing. Witloof roots can be refrigerated for up to 10 months before being removed and bud growth forced, as they remain dormant under cool conditions. Once given warmth and moisture in the form of a nutrient solution, the dormant apical buds will start to grow during the forcing process.
Hydroponic witloof: second stage
Hydroponic forcing of witloof to produce chiconsmust take place in complete darkness if high-quality, creamy white, blanched chicons are to be produced. Any light will result in greening of the chicons arising from the production of chlorophyll, which changes the flavor and lowers the quality of the witloof.
Under commercial production, hydroponic systems are run inside enclosed sheds with double-door entries to prevent any light from entering. In an indoor garden, witloof production can take place under benches or enclosed, lightproof boxes used to cover the developing buds. Hydroponic systems for witloof forcing set up in dark cellars or other areas can also work, particularly if an indoor garden is being lit to grow other plants and can’t be used for this process.
Once the witloof tap roots are removed from cold storage, they are trimmed to a consistent length of 6 to 8 in., packed side by side into deep trays, and a nutrient solution is applied so that it flows through the roots and out the base of the tray.
Nutrient solutions used during the forcing process provide essential nutrients for healthy bud and foliage development, giving a higher quality harvested product. At this stage, temperature is vital as it breaks the dormancy of the apical buds on the tap root system and starts the forcing process.
Nutrient solutions are typically warmed to 61 to 72°F, while the air temperature is kept a little cooler at 55 to 65°F with a high relative humidity of 90% (conditions often easy to maintain in a cellar). Under these conditions, the buds present on the roots will start to develop into short, compact shoots of white leaves.
This normally takes 20 to 22 days under ideal conditions. During this time, air flow is required around the hydroponic system while at the same time maintaining high humidity. For this reason, fogging or misting is often used to help keep air temperatures down and prevent the chicons from drying out and developing physical disorders such as tipburn.
Under commercial production, each 110 lbs. of roots being forced will produce approximately 18 lbs. of chicons, although not all buds may be of marketable quality. This yield ensures that harvested witloof chicons are considered a high-value delicacy and niche market crop.
At harvest, the chicons are carefully snapped from the roots and any loose outer leaves removed. At this stage, witloof should be 4 to 8-in. long and 1 to 3-in. wide, a whitish yellow color, compact and bullet shaped.
Once harvested, the tender chicons must be cooled immediately to prevent desiccation and prolong shelf life if being stored. Commercially produced chicons are wrapped in moisture-proof paper that excludes light and stored under refrigeration at a high relative humidity of 95 to 98%. Typically these will store for a maximum of two to three weeks under these conditions.
Ideally, home-grown, hydroponic witloof should be eaten within a few hours of harvest as this is when sugar levels will be highest and flavor and texture optimized. Freshly harvested whitloof chicons are a delicacy that few ever get to sample, and are a great reward for the time and effort invested in this unique crop.
Written by Lynette Morgan | Author, Partner at SUNTEC International Hydroponic Consultants
Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.