Tech Sheet for Geraniums
Fred Hulme, PH.D., Technical Service, ICL Specialty Fertilizer
Overall comments about Geraniums:
• Geraniums are heavy feeders especially during the vegetative stage.
• Typical problems are poor size and light green foliage due to inadequate
nutrition.
• Adequate magnesium will ensure dark green foliage.
• Some Geranium cultivars are sensitive to micronutrient toxicities especially
if root-zone pH’s drop below 5.8.
100% Water soluble fertilizer (WSF) program:
• Ideally fertilizer selection should be based on a current water analysis
(contact your ICL representative for more details).
• A good general program would be Peters Excel® 15-5-15 Cal-Mag at 200 to
250 ppm N on a constant basis.
• Commence feeding at planting or as soon as cuttings are rooted.
100% Controlled release fertilizer (CRF) program:
• Osmocote® Plus (5-6 mo. at 70°F in Northern zones/ 8-9 mo. at 70°F in Southern zones)
incorporated at 6 to 8 lbs. per cu. yard.
• Media should be used within 2 to 3 weeks after mixing in CRF.
• Select a longer term product to extend feeding once plants get shipped.
Combination fertilizer program:
• Osmocote® Plus (5-6 mo. at 70°F in Northern zones/ 8-9 mo. at 70°F in Southern zones)
incorporated at 3 to 6 lbs. per cu. yard.
• Fertigate with Peters Excel® 15-5-15 Cal-Mag at 100 to 150 ppm N on a
constant basis.
Supplements:
• Add Magnesium in form of Peters Excel® Magnitrate 10-0-0 @ 4 oz. per
100 gallons on a constant basis if Mg is lacking in program.
• Apply a medium rate of H2Pro® liquid before shipping to help prevent
wilting in the post-harvest phase.
Problem solving:
• If plants are chlorotic and pH is above 6.8; apply a low rate of Liquid
Stem (2 fl. oz. per 100 gallons).