In Dutch conditions the earliest chicory witloof plots (sown at the beginning of May) can be lifted from about 20 September, provided that the roots are sufficiently ripe. Cold storage (0-2 °C) for at least 14 days will be required for these lots. Flower induction takes place during the vernalisation period, which activates the inflorescence (pith). This process is required for the development of suitably-formed, firm chicons (= forcing).

High initial temperatures

In addition to the necessary pre-chilling, the first lots will also require fairly high initial temperatures to provide for the further activation of the pith. This temperature is required at the beginning of the forcing period to develop the pith. Initial water temperatures of between 20-22 °C are customary. The air temperature is usually 2-3 °C lower.
Maintain a higher air temperature during the first few days, if so required, since the growing point responds primarily to the air temperature at the beginning of the forcing period. Begin the nutrient schedule with about 2.5 mmol/l ammonium.
During the second half of the forcing period the temperature can be reduced as required to maintain control of the pith. The concentration of ammonium in the nutrient solution will then also need to be reduced. Take care with temperature jumps after 10 days. A late activation of the pith often results in open chicons, since the pith ‘opens' the chicons.

Very early varieties are sometimes riper than predicted. Anticipate this and take timely action. If after approx. 10 days the pith temperature has already risen to 1.5 - 2 °C above the water temperature then this is a sign of advanced ripeness. If the forcing temperatures are too high then this could lead to open heads. To prevent this, the water temperature and level of ammonium should be reduced earlier on in the current forcing period, and it may be that the following rows need to be started off at lower temperatures.

A gentler start in December

The longer the roots spend in chilled storage in December the riper they become, so lower temperatures will then be sufficient to develop the pith in December. Pith temperature checks allow you to estimate with reasonable accuracy when the chicory roots are becoming riper; if the roots become riper, the pith temperature can easily rise above that of the water. In addition, the early varieties will start to grow and open during the first 10 days.

The heat required to develop the pith decreases with the period in chilled storage, and consequently lower temperatures are needed in December. In December the initial water temperature is usually 19-20 °C.
Reduce the initial temperature further, and switch to a flatter schedule once the vernalisation is complete and the chicons developed during the first 10-15 days open excessively. See also Early forcing: Jan-Feb