Effect of potassium and potting medium on growth of golden pothos

University of Florida, IFAS,
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-91-14

Pothos (Epipremnum aureum) are produced by cuttings from stock plants frequently grown outside of Florida. When growers receive cases of these cuttings, they assume that if the cuttings appear to be of high quality they will root rapidly and grow into a salable unit within a standard period of time. Sometimes cuttings do not root and grow as expected due to diseases, shipping conditions, or pesticide toxicity. It is not uncommon to find that none of these factors can be identified as the cause of the problem. Previous work on nutrition of vining stock plants led to the following study on potting media and potassium effects on development of golden pothos stock plants and cuttings derived from them.

Rooted cuttings of golden pothos were obtained from commercial producers and established in Vergro potting medium. After rooting was well underway, they were transplanted to 6 inch standard plastic pots containing Vergro or a mixture of Canadian peat and pine bark (1:1 by volume). Each potting medium was amended with dolomitic lime and Micromax at the recommended rate. All plants received nitrogen (from NH₄NO₃) and phosphorous (from H₃PO₄) in the irrigation water once a week. Potassium treatments were also added to the irrigation water (from KC1) for those treatments receiving potassium. Treatments were set up in a factorial experiment with two potting media (Vergro and 1:1) and two potassium treatments (none and recommended level). Ten replicate pots were used for each of the four treatments. The first test was conducted between May and December 1990 and the second test between December 1990 and May 1991. Temperatures ranged from 70 to 95°F (Test 1) and from 60-90°F (Test 2). Light levels in Test 1 were from 1400 to 2000 ft-c and from 1200 to 1600 ft-c for Test 2.

Plants were rated periodically during the tests which lasted about 6 months each. Leachate soluble salts were recorded monthly. Plants were trimmed (vines were removed to within 3" of the pot rim) and the number, fresh weight and length of cut vines, as well as number of new breaks and top grade recorded for each test with the time depending upon the growth rate. The top grade was rated on the following scale: 1 (dead), 2 (poor, unsalable), 3 (moderate, salable), 4 (good, salable), and 5 (excellent, salable). In the first test, cuttings were rooted from the trimmed vines twice. They were placed, 10 per 6 inch pot containing Vergro and top-dressed with 6 g/pot of the slow-release fertilizer Osmocote 19-6-12. After 4 to 6 weeks under an intermittent mist, top grade was recorded using the scale described above.

The first cutting for Test 1 was made on 10 July about 4 weeks after the experiment was initiated. Three weeks later, the number of new breaks showed that plants receiving potassium had more breaks (Table 1). When plants were trimmed on 22 August, the number of vines removed was lowest for those in the 1:1 potting medium without potassium. Vine weight was best for the plants in the Vergro potting medium regardless of potassium treatment (Table 1). Cuttings removed at this time were rated for top grade after four weeks and showed no significant differences based on either the potting medium or potassium treatment. Vines were again trimmed on 23 October and at this time the vine weight showed an interactive effect of the potting medium and the potassium treatment with a dramatic growth reduction for the plants in the 1:1 medium which were not receiving potassium. Cuttings were also rooted from these vines and showed a similar trend in cutting grade at the 3 December rating (Table 1).

Results from the second test were similar although the damage incurred by the no potassium treatment appeared more quickly than in the first test.

Plants in Test 2 were potted and fertilizer treatments started on 17 December 1990. The first cutting date was on 13 February reflecting the relatively slower plant growth due to the cooler temperatures (60 to 90°F) and decreased light levels (about 1400 ft-c average) compared to those of Test 1. In this case, the vine length was significantly affected by the potting medium but not by potassium treatment (Table 2). Number of vines was unaffected by treatment at this rating. Plants were trimmed again on 12 March, when both potting medium and potassium treatment affected the fresh weight of vines, although no interaction occurred (Table 2). Number of vines was again only affected by the potting medium. No cuttings were taken from these plants, although top grade rated on 1 May showed a significant interaction between potting medium and potassium treatments.

In all cases, the poorest quality plants and cuttings generated from these "stock plants" were obtained when plants were potted in 1:1 potting medium and did not receive potassium. Vergro potting medium contains a small boost of fertilizer (containing potassium as well as other elements) which was not present in the 1:1 medium which we made from raw ingredients. Differences in the top quality of the cuttings established from potassium deficient plants appeared about 1 to 2 months before deficiencies appeared in the stock plants. Potassium deficiency in pothos is characterized by shortened internodes, stunted leaves (1 inch in length or less), leaf necrosis and finally plant death. In one test, the appearance of notable deficiency symptoms took six months, while in the other they appeared in four months. Prior to development of these symptoms, growth reduction appears with standard sized leaves and vine appearance. Pothos appear to be able to survive for 3 or more months without anymore potassium than is present in Vergro without growth reductions. Current recommendations for potassium levels in pothos may be higher than actually required by pothos for good growth; however, be especially careful not to lower rates to levels which support adequate stock growth but decreased cutting quality.

*Professor of Plant Pathology, and Professor of Environmental Horticulture, respectively. CFREC-Apopka, 2807 Binion Rd., Apopka, FL 32703-8504.

Treatment^a	No. breaks 27 July	No. vines 22 August	Vine weight(g) 22 August	Cutting grade^b 21 September	Vine weight 23 October	Cutting grade 3 December
Vergro, no potassium	11.7	8.7	132	4.7	216	3.9
Vergro, potassium	12.9	9.6	137	4.7	266	4.0
1:1, no potassium	11.3	8.1	104	4.0	79	2.3
1:1, potassium	13.8	8.9	111	4.6	210	4.1

Significance^c
Potting medium(P)	ns	ns	0.0001	ns	0.0001	0.0002
Potassium(K)	0.021	0.026	ns	ns	0.0001	0.0001
P x K	ns	ns	ns	ns	0.0001	0.0001

Treatment^a	Vine length(in) 13 February	No. vines 13 February	Vine weight(g) 12 March	No. vines 12 March	Top grade^b 1 May
Vergro, no potassium	49.0	3.1	130.9	5.2	4.7
Vergro, potassium	55.5	3.5	161.7	4.8	4.9
1:1, no potassium	35.2	3.0	62.0	4.3	2.4
1:1, potassium	44.2	2.9	114.2	4.0	4.0

Significance ^c
Potting medium(P)	0.049	ns	0.0001	0.02	0.0001
Potassium(K)	ns	ns	0.001	ns	0.0001
P x K	ns	ns	ns	ns	0.0001