Effect of potassium rate, temperature, and light on growth of Pothos

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University of Florida, IFAS,
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-91-11

A. R. Chase and R. T. Poole*

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 product within a standard period of time. However, sometimes cuttings do not respond as expected. Diseases, shipping conditions, or pesticide toxicity are blamed for poor rooting or plant growth, yet it is not uncommon to find that none of these factors can be identified as the cause of the problem. Previous work on nutrition and temperature tolerance of vining stock plants led to the following study on minimum winter temperature, chilling temperature, potassium rate and light levels on development of golden pothos.

Materials and Methods

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 and amended with dolomitic lime and Micromax at the recommended rate. Potassium treatments were top-dressed at the rate of 0, 2, 4, or 6 g (slow-release 0-0-45)/6 inch pot every two months. Nitrogen was added at the rate of 5 g (slow-release 39-0-0) and single superphosphate was added at the rate of 4 g/6 inch pot. Treatments were set up in a factorial experiment with four rates of potassium and four minimum air temperatures (60, 65, 70, or 75°F). Twelve replicate pots were used for each of the 16 treatments. The first part of the test was initiated on 12 December 1989 when fertilizer treatments were applied. Leachate soluble salts were recorded monthly. Plant ratings included number of vines, total vine length, and fresh weight of tops, all recorded between 19 and 23 January 1990. Half of each treatment was exposed to 1 week at 50°F to test sensitivity to chilling starting on 14 January 1990. The number of necrotic leaves and the number of distorted leaves were recorded on 23 January 1990.

The second part of the test commenced on 9 February 1990 when three of the remaining 6 replicates per treatment were moved to a higher light level condition. Temperature treatments were discontinued when the light treatment was initiated although the application of fertilizer treatments continued as described on schedule. Total vine length and fresh top weight were recorded on 30 April and 1 May 1990, respectively. Cuttings were rooted from the trimmed vines by placing 10 per 6 inch pot containing Vergro and top-dressed with 6 g/pot of the slow-release fertilizer Osmocote 19:6:12. After 5 weeks under an intermittent mist, top grade was recorded using the scale: 1 (dead), 2 (poor, unsalable), 3 (moderate, salable), 4 (good, salable), and 5 (excellent, salable).

Results and Discussion

Minimum winter temperatures between 60 and 75°F affected the growth of pothos in this test although the potassium rates tested did not appear to influence their growth (Table 1). In general, the higher the minimum night temperature the greater the number of vines, and vine length. In the case of the fresh weight of tops, however, the application of potassium did result in a trend toward greater growth as potassium level increased (Table 1). Neither minimum temperatures under which pothos were produced nor the rate of potassium supplied affected their tolerance of chilling at 50°F although a statistical interaction between the two factors appeared to occur (Table 1).

When the temperature treatments were discontinued on those plants which were not exposed to the chilling treatment, they were exposed to two light levels (3000 and 5500 ft-c). About 3 months after the light treatments were initiated, plant growth showed a significant response in the number of vines produced as well as the total vine length and fresh weight of tops (all decreased under the 5500 ft-c level) (Table 2). As potassium increased so did the top weight of the vines produced, which was similar to the results noted in the first portion of this experiment (Table 2). This was most notable under the 3000 ft-c and is likely explained by the fact that even the highest potassium rate was too low for optimum growth of pothos under 5500 ft-c. Finally, the cuttings collected from these plants were rated about 5 weeks later and results showed that those produced from plants under the higher light level were generally a higher quality. All plants showed a similar increase in quality as potassium rate increased.

Conclusions

Minimum winter temperatures for pothos between 60 and 75°F dramatically affected plant growth with increased growth response as minimum temperature increased. It did not, however, reduce sensitivity to chilling injury when exposed to 50°F for 1 week. Potassium level (even a lack of potassium) only affected the fresh weight of tops whether plants were grown under 3000 or 5500 ft-c. Even when low potassium rates did not appear to greatly reduce quality of the "stock plants" it did influence the ability of the cuttings removed from these plants to root and produce a salable product. Vergro potting medium contains a small boost of fertilizer (containing potassium as well as other elements) which could account for the lengthy time that plants grew in the "absence" of potassium without detriment to their growth. It was especially interesting to note that differences in the growth and appearance 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 several other experiments, the appearance of deficiency symptoms took 4 to 6 months. Prior to development of these symptoms, growth reduction as measured by fresh top weight, appears with standard sized leaves and vine appearance. Newly established pothos stock plants appear to be able to survive for 3 or more months without any additional potassium than is present in Vergro. Current recommendations for potassium levels in pothos may be higher than actually required by pothos for good growth when appropriate light levels are maintained. Be especially careful not to lower rates to levels which support adequate stock growth but decrease cutting quality.

*Professor of Plant Pathology, and Professor of Environmental Horticulture, respectively. Central Florida Research and Education Center-Apopka, 2807 Binion Rd., Apopka, FL 32703-8504.

^a The lowest temperature allowed in each section is given.
^b Potassium (0-0-46 slow-release formulation) was applied at the rate given in g/6 inch pot twice during the duration of the test.
^c Total vine length was recorded on 19 January 1990.
^d Fresh weight of vines was recorded on 23 January 1990.
^e Number of leaves showing symptoms of necrosis following chilling treatment (1 week at 50°F) were recorded on 23 January 1990.
^f Number of leaves showing symptoms of distortion following chilling treatment (1 week at 50°F) were recorded on 23 January 1990.
^g Significance of the analysis of variance (F value) is given. Numbers less than 0.05 are considered significant.

^a Light level is given in foot candles.
^b Potassium (0-0-46 slow-release formulation) was applied at the rate given in g/6 inch pot once at test initiation.
^c Total vine length was recorded on 30 April 1990.
^d Fresh weight of vines was recorded on 30 April 1990.
^e Cutting grade was rated on the following scale on 7 June 1990; 1 (dead), 2 (poor, unsalable), 3 (moderate, salable), 4 (good, salable), and 5 (excellent, salable).
^f Significance of the analysis of variance (F value) is given. Numbers less than 0.05 are considered significant.