Callused Geranium Cuttings: Tips For Successful Rooting

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'Americana Pink' geranium from Syngenta

Growers are always looking for opportunities to improve production efficiency and reduce costs. One option is to use callused cuttings when producing vegetative geraniums. The key advantage of starting with callused instead of unrooted cuttings is that they can be directly stuck into the finish container without the need for an automated misting system. Additional benefits include reduced shrinkage and more uniform rooting.

Upon Arrival

Upon arrival of callused cuttings, boxes should be unpacked and cuttings stuck immediately. If that is not possible, opened boxes should be stored at 36 to 38°F for no longer than 24 hours. Longer storage duration can cause excessive leaf yellowing and loss of cuttings. When a cooler is not available for temporary storage, the bags should be opened and the cuttings should be laid on the bench and frequently misted well.

Sticking

Callused cuttings can be directly stuck into a final container filled with a growing media that has good water-holding capacity and aeration such as Fafard 1P Mix, 2 Mix, 3B Mix or 4P Mix. The recommended media pH is 6.0 to 6.4 (saturated media extract) for zonal geraniums, 5.4 to 5.8 for ivies and 5.8 to 6.2 for hybrid geraniums such as the Calliope series.

On the day prior to sticking cuttings, irrigate pots to ensure media moisture is at level 4 (media is wet, but water is not easily observed when pressed). Maintaining good moisture levels in only the top half of the container will result in good aeration, fast rooting and minimal losses. If the media remains too saturated, there is greater risk for Botrytis on stems and leaf petioles.

Rooting

After cuttings are stuck, apply enough mist to hydrate the leaves. Once roots begin to form, consider an application of a preventive fungicide drench such as Subdue Maxx at 1 ounce/100 gallons to avoid any problems with Pythium. If cuttings arrived warm or stressed, Fascination can be sprayed at 2 ppm to help reduce leaf yellowing.

On days three to five after stick, check cuttings every 30 to 45 minutes for wilting and mist lightly by hand as needed. Use a misting nozzle that produces a fine mist or fog since regular watering nozzles will cause the media to become oversaturated. While helpful, automatic misting systems are generally not needed for rooting callused geranium cuttings. Keep light levels at 2,000 foot candles. For fast rooting, maintain 80 percent relative humidity, media temperature at 70 to 74°F and air temperature at 65 to 75°F.

After cuttings are rooted, misting can be stopped and shade cloth removed. Light levels can be increased to 3,500 to 4,000 foot candles. During this stage, air temperature should be maintained at 70 to 75°F day and 65 to 68°F nights. Begin fertilization at 150 ppm nitrogen using a calcium-magnesium nitrate formulation. As roots reach the bottom of the container, the fertilizer rate can be increased to 200 to 250 ppm nitrogen. The target media electrical conductivity (EC) should be 2.0 to 2.5 mS/cm. As the crop develops, perform a media analysis and check that pH and EC are within the correct ranges. About two weeks after sticking, consider applying a plant growth regulator such as Florel or Cycocel to increase branching and reduce stem extension.

Matthew Blanchard is a postdoctoral research associate in the Department of Horticulture at Michigan State University. You can eMail him at mgblanch@msu.edu.

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