Effects of Lime Source on pH of Growing Medium During Production of Dieffenbachia maculata 'Camille'

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University of Florida/IFAS
Central Florida Research and Education Center
CFREC-Apopka Research Report RH-95-5

C.A. Conover*

When purchased, the pH of most commercially manufactured soilless growing medium used for foliage plant production is usually around 5.5 to 6.5 because lime has been incorporated into the product to counteract acidity of other mix components. However, growing medium pH tends to drop over time if acidic irrigation water and/or fertilizers are used. Although good quality plants have been observed growing in mixes having a low pH, this condition could slow down conversion of ammonium to nitrate and influence phosphorous and micronutrient nutrition. Decreasing growing medium pH over time could become a serious problem for stock plants in production areas where plants remain in the same medium for extended periods.

When pH of growing medium in containers of foliage plants needs to be raised during production, calcium hydroxide has often been suggested as a surface application to correct the problem. However, in an earlier test, calcium hydroxide was not effective for rapid pH adjustment. Several months were needed to raise medium pH using surface applications. Final plant quality was lower for treated compared to untreated plants and Dieffenbachia maculata 'Camille' grew less as calcium hydroxide application rate and number of applications increased (Poole and Conover, 1992).

In the following test, a growing medium amended with 0.0, 2.5 or 5 lbs/yd3 (0.0, 1.48, 2.96 kg/m3) dolomitic limestone to which various rates of calcium hydroxide, calcium carbonate or Limestone-F (W.A. Cleary Chemical Corp., Somerset N.J. 08873) were surface applied was used to produce Dieffenbachia maculata 'Camille' (Camille dieffenbachia). Limestone-F is a flowable micronized dispersion containing 6 lbs/gal dolomitic limestone (active ingredients 27.1% calcium carbonate and 22.9% magnesium carbonate). Leachate was collected from the medium periodically to determine effects of the three calcium products over time on pH of growing medium amended with dolomite at various rates.

The experiment began on October 23, 1992, when tissue cultured liners of Camille dieffenbachia were transplanted, one per pot, into 6-inch (15-cm) containers. Growing medium used was composed of Florida sedge peat:builder's sand (3:1 v/v) only or the same Florida sedge peat:builder's sand formulation amended with 0.0, 2.5 or 5.0 lb/yd3 (1.48 or 2.96 kg/m3) dolomite. Calcium supplement treatments were surface applied to the growing medium at 1x or 2x rates (see Table 1 for growing mix formulations), one month after transplanting. Including the control group which contained no amendments, nineteen medium treatments with five replications per treatment were used.

Plants were grown to salable size in a glass greenhouse where air temperatures ranged from 70 to 90F (21 to 32C) and maximum light intensity was about 1500 ft-c (200 mol•m-2 •s-1). Growing medium was top-dressed with 6 g/6-inch pot (2.1 oz/15-cm pot) 19-6-12 Osmocote (The Scotts Company, 6656 Grantway, Allentown, PA 18106) on October 23, 1992, and again on January 14, 1993. Plants were watered two or three times a week as needed to maintain healthy growth. On November 20, 1992, a 100 ml suspension containing Ca(OH)2, CaCO3 or Limestone-F, at the 1x or 2x rates shown in Table 1, was poured over the growing medium surface in each container.

Plant height was measured initially on November 10, 1992, and again when the experiment was terminated on June 3, 1993. Plant growth (cm) was determined using the formula; final height - initial height = plant growth. Plants were graded using the scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality. Camille dieffenbachia were graded three months after transplanting, on February 26, and again six months after transplanting, on May 26, 1993. Electrical conductivity (mhos/cm) and pH of the growing medium leachate were determined on December 2, December 17, 1992, January 14, February 12, March 10, April 7, May 5 and June 3, 1993.

Results

Final height, growth and final plant grade were not significantly affected by calcium supplement type or application rate. Slightly larger, better quality plants were produced in growing medium containing calcium supplements, as dolomite incorporation rate increased (Table 2). Plant grade of Camille dieffenbachia grown in medium containing no calcium supplements or dolomite (the control group) was much lower compared to plant grade of Camille getting dolomite or any of the treatments getting a supplement only.

The pH of leachate collected from growing medium of Camille dieffenbachia was higher as dolomite rate increased (Table 3). Supplement type or application rate did not significantly affect pH of growing medium leachate. As time passed, electrical conductivity of the growing medium leachate decreased as dolomite incorporation rate increased (Table 4). Supplement type affected electrical conductivity only initially, when Camille Dieffenbachia getting CaCO3 had slightly higher medium electrical conductivity compared to Camille dieffenbachia getting Ca(OH)2 or Limestone-F (data not shown). Otherwise, EC was not significantly affected by supplement rate.

Interactions of calcium supplement type and supplement application rate significantly influenced pH of growing medium leachate collected on January 14 and March 10, 1993 (Tables 5 and 6). On January 14, 1993, pH of growing medium leachate for low supplement rate treatments were similar. Doubling supplement rate produced higher pH readings for CaC03 or Limestone-F treatments but pH was slightly lower for leachate from the Ca(OH)2 treatment (Table 5).

Effects of an interaction of supplement type and rate on pH of leachate collected on March 10, 1993, was similar to the effects of the interaction described above (Table 6). Again, doubling supplement rate produced higher pH readings for CaC03 or Limestone-F treatments, but doubling rate of the Ca(OH)2 application did not raise pH of the leachate.

Conclusions

The interactions of supplement type and application rate suggest that calcium carbonate or a product containing calcium carbonate could be more effective in raising pH of growing medium compared to the use of calcium hydroxide if the application rate of calcium hydroxide needed to raise pH to the desired level would be more than 2 g/6-inch pot.

Dolomite in the growing medium supplied Camille dieffenbachia with both calcium and magnesium. This could be why increasing dolomite rate, even in growing medium of plants getting calcium supplements, increased plant quality and growth. Plants getting calcium supplements only were of much better quality than plants getting no calcium but did not receive as high of plant grades compared to plants getting dolomite.

*Center Director and Professor of Environmental Horticulture (retired 7/96), Central Florida Research and Education Center, 2807 Binion Road, Apopka FL 32703-8504


References

  1. Conover, C.A., R.T. Poole and R.W. Henley. 1991. Light and fertilizer recommendations for theinterior maintenance of acclimatized foliage plants. Southern Nursery Digest 26(5):25-26, 52-53.
  2. Joiner, J.N., C.A. Conover and R.T. Poole. 1981. Nutrition and fertilization. Chapter in: Foliage Plant Production, J.N. Joiner ed., Prentice-Hall Inc., Englewood Cliffs, NJ.
  3. Poole, R.T. and C.A. Conover. 1992. Changing medium pH with hydrated lime. Univ. of Fla., IFAS, CFREC-Apopka Res. Rpt. RH-92-l.
  4. Wright, R.D. 1983. Study indicates need for changes in nutrition programs for plants in containers. Amer. Nurseryman 157(1): 109-111.

Table 1. Growing medium treatments used to grow Dieffenbachia maculata 'Camille' from October 23, 1992 until June 3, 1993. Basic growing medium was composed of Florida sedge peat:builder's sand (3:1 v/v).

Treatment
no.
Dolomite, lbs/yd3 Calcium
supplement
Supplement ratez,
g or m1/6-inch pot
1 Control group, no amendments or supplements added
2 0.0 Ca(OH)2 2 g
3 0.0 Ca(OH)2 4 g
4 0.0 CaCO3 3 g
5 0.0 CaCO3 6 g
6 0.0 Limestone-F 3 ml
7 0.0 Limestone-F 6 ml
8 2.5 Ca(OH)2 2 g
9 2.5 Ca(OH)2 4 g
10 2.5 CaCO3 3 g
11 2.5 CaCO3 6 g
12 2.5 Limestone-F 3 ml
13 2.5 Limestone-F 6 ml
14 5.0 Ca(OH)2 2 g
15 5.0 Ca(OH)2 4 g
16 5.0 CaCO3 3 g
17 5.0 CaCO3 6 g
18 5.0 Limestone-F 3 ml
19 5.0 Limestone-F 6 ml

zSupplement treatments were surface applied to growing medium, on November 20, 1992. For each container, the amount of supplement applied was first used to make a 100 ml suspension, which was then poured over the growing medium surface.


Table 2. Effect of dolomite on final height, growth and plant grade of Dieffenbachia maculata 'Camille' grown in medium treated with calcium supplements. Plants were grown from October 23, 1992, until June 3, 1993, with calcium supplements surface applied to the growing medium on November 20, 1992.

Dolomite rate Final htz
(cm)
Growthy
(cm)
Plant
gradex
0.0 36.0 21.2 4.0
2.5 38.1 22.2 4.6
5.0 38.2 22.6 4.8
Significancew      
linear ** * **

zFinal height was measured on June 3, 1993. Final height of the control group, grown in medium without dolomite or calcium supplements, was 35.2 cm.
yPlant growth was determined using the formula final height - initial height = plant growth. Plant height was measured initially on November 10, 1992. Growth of the control group was 20.1 cm.
xPlants were graded based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality, on May 26, 1993. Plant grade of the control group was 3.4.
wns, *, **; Nonsignificant, significant at P = 0.05 or significant at P = 0.01, respectively.


Table 3. Effects of dolomite rate on pH of leachate from containers of Dieffenbachia maculata 'Camille' grown using calcium supplements. Plants were grown from October 23, 1992 until June 3, 1993, with calcium supplements surface applied to the growing medium on November 20, 1992.

Dolomite rate,
lbs/yd3
Dec
2
Dec
17
Jan
14
Feb
12
Mar
10
Apr
7
May
5
Jun
3
0.0 3.4 3.5 3.4 3.2 3.2 3.1 2.9 2.8
2.5 4.1 3.9 3.8 3.3 3.5 3.2 3.1 3.0
5.0 4.5 4.6 4.4 3.9 4.3 3.9 3.8 3.5
Significancez                
linear ** ** ** ** ** ** ** **
quadratic ** ** ns ns ns * ns ns

zns, *, **; Nonsignificant, significant at P = 0.05 or significant at P = 0.01, respectively. The pH of leachate collected from containers of the control group (grown in medium without dolomite or calcium supplements) on the same dates was 3.3. 3.3. 3.3. 3.1. 3.3. 3.2. 2.9 and 2.8.


Table 4. Effects of dolomite rate on electrical conductivity (ymhos/cm) of leachate from containers of Dieffenbachia maculata 'Camille' grown using calcium supplements. Plants were grown from October 23, 1992, until June 3, 1993, with calcium supplements surface applied to the growing medium on November 20, 1992.

Dolomite rate,
lbs/yd3
Dec
2
Dec
17
Jan
14
Feb
12
Mar
10
Apr
7
May
5
Jun
3
0.0 2569 2269 2244 2620 2194 1970 2016 1533
2.5 2771 2601 2603 2909 2150 2128 1704 1003
5.0 2660 2067 2429 2687 1559 1852 1311 794
Significancez
linear ns ns ns ns ** ns ** **
quadratic ns ** ns ns ns ns ns ns

zns, *, **; Nonsignificant, significant at P = 0.05 or significant at P = 0.01, respectively. Electrical conductivity of leachate collected from containers of the control group for the same dates was 2928, 2505, 2262, 3052, 2343, 2307, 2308 and 1892.


Table 5. Effects of interaction of supplement type and rate on pH of leachate collected on January 14, 1993, from containers of Dieffenbachia maculata 'Camille'.

Supplement Supplement
rate 1x
Supplement
rate 2x
Ca(OH)2 3.7 3.6
CaCO3 3.8 4.2
Limestone-F 3.6 4.4

Results significant at P = 0.0015. pH of leachate collected on January 14 from containers of the control group was 3.3.


Table 6. Effects of interaction of supplement type and rate on pH of leachate collected on March 10, 1993, from containers of Dieffenbachia maculata 'Camille'.

Supplement Supplement
rate 1x
Supplement
rate 2x
Ca(OH)2 3.6 3.6
CaCO3 3.7 4.0
Limestone-F 3.4 3.8

Results significant at P = 0.0206. pH of leachate collected on March 10 from containers of the control group was 3.3.