The effect of planting date on growth, seed stalk development and yield of sweet fennel

To study the growth and development of sweet fennel (‘ZEFA-Fino’ and ‘ZEFA-Tardo’) seedlings were raised under greenhouse conditions (night temperature 16—18°C) and planted out at 3—4 true leaf stage on May 21st, June 10th, July 7th and July 27th. The effects of covering mulch and short day treatment of seedlings were studied also. First harvests were performed when field measurements showed that the greatest width of ‘ZEFA-Fino’ bulbs were on average 60 mm. Three harvests were then performed at one week intervals. Plant and bulb weights, bulb greatest width and thickness and, the heights of plant, bulb and stem inside the bulb was measured. The number of bolters were recorded. The bulb width of ‘ZEFA-Fino’ reached 60 mm in 1.5—2 months after planting out depending on planting date. Plant and bulb weights, bulb width and thickness, stem height inside the bulb and the bulb height in the earliest plantings increased as the growth period lengthened. The bulb width of ‘ZEFA-Fino’ was in higher correlation with bulb weight than bulb thickness or height. The ratio between the height of stem inside the bulb and bulb height increased fastest in the lot planted under cover in May and in the lot planted out in June; at the fourth harvest the relationship was 0.8. The largest number of bolters (8 %) was found in the latter lot. The yield estimate for ‘ZEFA-Fino’ at the third and fourth harvest was 170—360 kg/are depending on planting date and length of the growing season. All lots of ‘ZEFA-Tardo’ except that planted in July bolted quickly after the bulb width had grown to 60—70 mm. The yield quality of ‘ZEFA-Tardo’ was low because of elongated bulbs and great variation in bulb height. Short day treatment (dark period 16 h) of the seedlings retarded but did not inhibit bolting of ‘ZEFA-Tardo’