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Postharvest trials showed marked differences in the length of vase life and in bud opening of Freesia stems of the same cultivar, obtained at a similar time from various nurseries. The factors that cause these differences in vase life and bud opening are yet unknown. We therefore made a detailed comparative investigation on the effect of greenhouse conditions. Corms of Freesia 'Yvonne' from the same stock were delivered to 29 nurseries. Various factors in the greenhouse that may influence vase life and bud opening were monitored. The vase life and bud opening of both the main and the lateral stems were examined with and without transport simulation. Using multivariate statistical techniques, the measured greenhouse conditions were related with the variance in vase life and bud opening. The main factors affecting vase life and bud opening were temperature, light level, CO 2 level, and relative humidity. The values of these factors during the last two weeks of production explained about half of the variance in bud opening and vase life. The results provide useful advise for growers on how to optimise greenhouse conditions in order to get the best possible postharvest quality of their product. INTRODUCTIONCut Freesia stems, even those of the same cultivar, show large differences in vase life and bud opening (van der Pluijm, 1993).This makes it hard for Freesia growers to guarantee the quality of their product. Sytsema-Kalkman (PPO Glasshouse Horticulture, unpublished) showed that the origin of the corms resulted in only small differences in vase life, and she concluded that the major differences were due to greenhouse conditions. In cut roses a similar situation exists, and here a comparison between nurseries proved to be a good tool to determine the correlation between quality and greenhouse conditions (Marissen and Benninga, 2001).

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For on-line plant monitoring equipment to be functional in commercial glasshouse horticulture, relations between sensor readings and plant responses on both the short (days) and long term (weeks) are required. For this reason, systems were installed to monitor rockwool grown gerbera plants on a minute-to-minute basis from July 2002 until April 2003. Data collected included, amongst others, crop transpiration from lysimeter data (2 m 2 ), canopy temperature using infrared sensors, rockwool water content, and greenhouse climatic parameters, such as global radiation and temperature. By combining data from lysimeter and water content, changes in crop fresh weight could be calculated on a daily basis. Both transpiration and daily fresh weight production were better related to light integral as measured inside the greenhouse, than outside the greenhouse. The contribution of heating pipes underneath the canopy to transpiration could be estimated with the system. From the relation between daily FW production and previous day light integral, a light use efficiency of ca. 10-g FW/MJ solar radiation as measured inside the greenhouse was calculated. Water use efficiency was on average 25 g FW/L. A 3-4 day drying cycle did not affect flower production. The results underline the importance of knowledge on the adaptation and tolerance of crops to stressful conditions, in order to be able to use plant monitoring under grower conditions effectively.

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