Dutch Iris are excellent for cut flower forcing since they deliver a high yield per square foot in a relatively short period. All varieties can be grown as an outside crop. Only certain varieties are suitable for greenhouse production of which the sizes 9/10 and 10/+ cm will give the best results. Varieties that can be forced in a greenhouse require a particular pre-cooling period, which differs per variety. We can provide this service.

Growing Area and Planting

Greenhouse iris bulbs can be planted in containers, trays or ground beds on 3 inch centers and only 1 1/2 inch deep. Use a well ventilated greenhouse that allows for plenty of sunlight. Run it at 55 F at night and 65 F during the day for best results.

Iris bulbs used for field production have to be planted outside in the fall as soon as the soil temperature drops below 55 degrees Fahrenheit. Plant bulbs outside at least 4" deep. In areas where the frost penetrates the soil deeper then 4" you can plant as deep as 6".

Cover the bulbs that are planted outside with mulch, straw or hay to protect planted bulbs from the frost.

Timing

Iris that are forced in the greenhouse take approximately 7 to 9 weeks for the early and medium varieties and up to 10-11 weeks for the late varieties.

Outside Iris will flower as early as the beginning of March for zone 8 and as late as the end of May for Zone 5.

In areas where the frost penetrates the soil too deep, Iris can be planted in the spring after the soil is thawed. However, these iris will require some pre-cooling and some shade towards the end of their flowering period.

Soil Requirements and Watering

Use a pH 6.5-7.0 sterile, well draining planting medium. Water thoroughly right after planting and keep soil slightly moist until signs of vigorous growth are visible, then increase watering. Always irrigate in the morning, so the crop can dry during the day.

Fertilizing

Fertilizing can start as soon as the plants have established a healthy root system. A slow release fertilizer (13-13-13) or 2 lbs. of calcium nitrate per 100 gallons of water can be used. Fertilize every other week during the growing season.