Sunday, March 30, 2008

Greenhouse - New Guinea Impatiens Culture

The following are some tips on growing good New Guinea Impatiens for greenhouse growers. Information is from the University of Maryland.

New Guinea Impatiens

We have moved into New Guinea season, and here are a few reminders. First off, do not fertilize New Guinea impatiens until the roots hit the bottom or sides of the pot. Then start feeding at 100 ppm. Grow them on the dry side and do not pinch the plants.

Fertilization in April and May:

• Adjust for pot size and space plans
• Bench Crops – do not want tall, lush plants, bypassing buds. 100-150 ppm N, rotating with clear water, EC .85-1.1 microsemens
• Bench Crops (after spaced) – can tweak feed up slightly 100-150 ppm N, clear water leach after 2-3 feeds, EC 1.0 – 1.25 microsemens
• Baskets/Containers – 150-250 ppm N, clear water leach after 3-4 feeds, EC 1.0-1.5
• At these rates, New Guineas can handle the NH4 from a typical 20-10-20 with positive results.
• Clear water in rotation to avoid build-up of salts

Light is Critical for good Quality:

• 3,500 – 5,500 foot candles is ideal
• If you have less than 3,000 foot candles, you’ll end up with poor-flowering, leggy plants
• If light is greater than 6,000 f.c., you will end up with reduced flower size and the potential for scorching
• If you have a heavy canopy of baskets in the greenhouse and try to grow New Guineas on the bench below, it may hinder flowering. Keep basket canopies somewhat open by alternating the heights of the baskets so it does not block light to plants below.

Spacing of New Guineas:

• Start out growing New Guineas next to each other with 4.5” space within the flat. Take out every other plant as they mature to increase the spacing to 7- 8”.
• If using a 6-6 ½” pot, move the spacing to 10-12” as the plants fill in.
• Hanging baskets may start on the bench, but move them to a 21-24” spacing to develop the fullest plants.

Reprinted in part from the March 28, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension. Go to for the full issue.

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