Response of African Violets to Fertilizer Source and Rate

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University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report RH-90-5

R.T. Poole, C.A. Conover, and Y. Ozeri*

Saintpaulia ionantha spp. (African violets) are commonly grown using capillary mat watering systems. Incorporated slow-release fertilizer is a recommended method of fertilization when plants are grown on capillary mats. This experiment examined African violet response to 3 sources of incorporated slow-release fertilizer and compared 5 application rates for each of the 3 fertilizers tested.

Fertilizers tested were: (1) Osmocote 13-13-13, an 8 to 9 month fertilizer; (2) Osmocote 14-14-14, a 3 to 4 month fertilizer; and (3) a combination of the two materials in a 1:1 ratio by weight. Osmocote is manufactured by Sierra Chemical Co., Milpitas, CA. Five application rates compared were 0, 0.32, 0.64, 0.96, and 1.28 grams per 4 inch pot of incorporated material. Plantlets of 6 African violet cultivars, California, Crater Lake, Everglades, Glacier, Texas, and Washington, were potted into 4 inch pots containing Verlite container mix. Verlite container mix is a peat vermiculite soil mix manufactured by Verlite, Tampa, FL. All cultivars were tested during two seasons, one warm, one cool. Plants were grown on capillary mats in a glass greenhouse under a maximum of 800 to 1200 ft-c and temperatures of 65F to 95F depending on season of year. Experimental data recorded for both the cool and warm season tests after 2 months included plant grade on a 1-5 scale (1=poor quality, 5=excellent quality), number of flowers and leaves, days to flower, leaf area, and leaf weight.

Source of fertilizer used produced variable results with only 23 of 72 indicators recorded showing significance. Thus, sources of fertilizer tested do not appear to be an important factor in this experiment.

Fertilizer application rate did produce significant differences for most factors evaluated. Because of the similarity of results among cultivars, only results from Everglades are shown (Table 1). The lowest rates tested, 0 and 0.32 grams per 4 inch pot almost always produced low quality plants. The 0.64 grams per 4 inch pot rate sometimes produced plants as good as those receiving the higher rates but the highest quality plants received 0.96 or 1.28 grams per 4 inch pot. The higher 1.28 grams per 4 inch pot rate was slightly more beneficial during the warm season planting but not during cool season production.

Number of days to flower was not affected by fertilizer rate. Plant grade, number of flowers, number of leaves, leaf area, and leaf weight increased with increasing fertilizer application rates. (Table 1) .

Results of these tests show good quality African violets can be produced in about 2 months during the winter or summer using either the 3 to 4 month or the 8 to 9 month Osmocote at application rates of 0.96 or 1.28 grams per 4 inch pot.

*Professor, Plant Physiology and Center Director and Professor, respectively, Central Florida Research and Education Center, 2807 Binion Road, Apopka, Florida 32703-8504, and Professor, Ornamental Horticulture, The Volcani Center, Bet Dagan, Israel 50250


1. Andersen, H. 1984. The effects of temperature, frequency of watering, composition of fertilizer and peat type on Saintpaulia. Tdisskrift Plant. 88:183-191.

2. Conover, C. A. and R. T. Poole. 1977. Influence of irrigation method and fertilizer source and level on growth of four foliage plants. Proc. Fla. State Hort. Soc. 90:312-313.

3. Conover, C. A. and R. T. Poole. 1981. Light acclimatization of African violet. HortScience 16:92-93.

4. Milde, H. 1980. Saintpaulias, a comparison of slow-release fertilizers. Vergleich von Langzeitdungung 80:486-488.

5. Payne, R. N. and S. M. Adam. 1980. Influence of rate of placement of slow-release fertilizer on pot plants of African violet grown with capillary mat watering. HortScience 15:607-609.

6. Schwemmer, E. 1980. Saintpaulia ionantha in hydroculture. Deutscher Gartenbau 34:1046-1047.

Table 1. Response of African Violet EvergladesZ to fertilizer source and rate.
Days to
A (in2)
wt (oz)
Planted Mar 22X
Fertilizer source
1 & 2, 1:13.646502259.81.2
Fertilizer rate
g/per 4 in pot
Planted July 10W
Fertilizer source
8 to 9 mo
3 to 4 mo
1 & 2, 1:13.680582076.41.4
Fertilizer rate
(g/per 4 in pot)

    ZSimilar data was also obtained for the cultivars, California, Crater Lake, Glacier, Texas, and Washington.
    Y1=poor quality, 5=excellent quality.
    XData taken June 8.
    WData taken Sept- 21.