Managing Greenhouse Nutrition Paul A. Thomas and Bodie V. Pennisi Extension Horticulture Specialists - Floriculture The University of Georgia

Modern Production Growers should NOT have nutritional problems

Why do we still have problems? Focus on solving problems Focus on solving problems Need to shift focus to PREVENTING problems Need to shift focus to PREVENTING problems

What to Look For Things that will impact plant nutrition Things that will impact plant nutrition Chemical characteristics Chemical characteristics  pH - water, fertilizer solution  EC - water, fertilizer solution  alkalinity - water, fertilizer solution Nutritional value Nutritional value  macronutrients, micronutriens Non-nutritional elements – possible toxicities Non-nutritional elements – possible toxicities  Na, Cl, F, Al

Expressed in ppm, mg/L, meq/L Expressed in ppm, mg/L, meq/L Expressed as CaCO 3 or HCO 3 - Expressed as CaCO 3 or HCO 3 - AlkalinityAlkalinity Irrigation water should have an alkalinity of less than 100ppm; if higher than 150 ppm, acidification is needed Irrigation water should have an alkalinity of less than 100ppm; if higher than 150 ppm, acidification is needed

A measure of water’s ability to neutralize acids – a buffering ability A measure of water’s ability to neutralize acids – a buffering ability Mostly carbonates and bicarbonates – associated with Ca and Mg (limestone) Mostly carbonates and bicarbonates – associated with Ca and Mg (limestone) May cause pH to rise in media over time, especially in small containers May cause pH to rise in media over time, especially in small containers AlkalinityAlkalinity Note: Alkalinity “controls” pH Must know alkalinity to manage pH

The Goal Is To Achieve A Stable Medium pH Over Time

Alkalinity Terms Milliequivalents alkalinity mg/liter or ppm CaCO 3 of alkalinity mg/liter or ppm bicarbonate

Sample A Sample B pH = 9 pH = 7 One drop of acid to get pH 6 Ten drops of acid to get pH 6 The Effect of Water Alkalinity on Media pH and Acid Requirement Little or no effect on the growing medium pH Increases growing medium pH Alk = 50 ppm Alk = 300 ppm

CaMg(CO 3 ) 2 Dolomitic limestone Ca 2+ + Mg CO 3 2- Hardness Alkalinity Hardness and Alkalinity Generally Go Hand-In-Hand but They Are NOT One and the Same You Can Use the Water Hardness to Estimate Its Alkalinity

 Calcium and magnesium are the major contributors  “hard water” has a high Ca and/or Mg  “hard water” is generally associated with high alkalinity  can have hard water and low alkalinity – water high in CaCl 2 and/or MgCl 2 HardnessHardness

 If you have hard water:  check Ca and Mg concentrations  if high use less lime  monitor pH !  check Ca : Mg ratio  ideal ratio is 3:1 if expressed in meq/L  ideal ratio is 5:1 if expressed in ppm HardnessHardness

H 2 CO 3 2CO H + H 2 O + CO 2 Substrate Acidity Alkalinity Both the alkalinity and the acidity are neutralized

Poinsettia Crop 10 Weeks After Planting (adopted from Greenhouse Grower, January 2001, p.72) Leaching Fraction Media pH The more water applied to the crop, the greater effect high alkalinity water will have on media pH. Initial media pH = 6.0 Water alkalinity = 320 ppm CaCO 3

 pH affects the solubility of fertilizers, and the efficacy of pesticides and growth regulators.  the higher the water pH the less soluble these materials are pHpH

Dealing With High And Low Water Alkalinity

Action Steps To Correct High Alkalinity reverse osmosis acid injection acid fertilizer and/or none less lime Alkalinity (ppm) bicarbonate

 If acid injection required, use the Alkalinity Calculator found on: oftware/ Correcting High Alkalinity

 Most commonly used acids: sulfuric, phosphoric, nitric.  Need to consider the extra phosphorus (P), nitrogen (N), or sulfur (S) in the acid when selecting fertilizer.  3.4 fl oz of 85% phosphoric acid/100 gal adds 122 ppm P to the irrigation water  If acid is changed, nutritional program needs to be re-evaluated. Correcting High Alkalinity

Other Factors

SalinitySalinity  Total Dissolved Salts (TDS) – all salts present in the water (1 mMho/cm=640 ppm)  less than 0.75 mMho /cm for plugs  less than 1.0 mMho /cm for other greenhouse crops  less than 2.0 mMho /cm for other nursery crops

Managing High Salinity in Water Supply  Dilute with collected rainwater or other low salinity water sources  Use reverse osmosis water treatment, particularly for misting cuttings, irrigating seedlings, and salt-sensitive crops

Where Does The Water Come From ?

Soil Zone Sand and Gravel Aquifer Limestone or Granite Aquifer Sandstone Aquifer Examples of Variation in Groundwater Quality Well # 1Well # 2Well # 3

Frequency % Irrigation Water Alkalinity concentrations (ppm CaCO 3 ) from Florida <40 40– >400

Testing The Waters …

Testing Water Quality In-House  Range 0-8 meq/L (0-400 ppm alkalinity expressed as CaCO 3 )  Accuracy  0.4 meq/L or better  Kits from $30 for 100 tests to $155 for 100 tests. $155 for 100 tests.

Commercial Lab

1.Need test for alkalinity 2.Need Fluorine (F) and/or Chlorine (Cl) if high levels are suspected.

Testing The Soil Solution !

Simple technique for measuring pH and EC Simple technique for measuring pH and EC Charts for recording pH & EC Charts for recording pH & EC Guidelines for crops Guidelines for crops Procedures to keep on track Procedures to keep on track Measuring Technique

6 or 8-inch saucers are adequate for collecting the leachate

Distilled Water Volumes 4 inch 5 inch 6 inch 6.5 inch 1 Qt 4 Qt 12 Qt Pot Size mloz

Flats: Use 50 ml Distilled Water

EC Comparisons 0 to to to to to 2.3 > 2.3 1:2SME PourThru Indication 0 to to to to to 6.0 > to to to to to 7.8 > 7.8 Very Low LowNormalHigh Very High Extreme

Monitoring Questions Number of samples? Number of samples? How often? How often? Options? Options?

How to Monitor Sample plants with different requirements separately Sample plants with different requirements separately  pH: acidic vs basic  EC: high vs low Randomly select plants Randomly select plants Select plants from interior of bench Select plants from interior of bench

Monitoring: the Key...  Have a manageable plan  Consider monitor and managing to be your insurance policy

Initial EC

Crop pH Ranges

Geraniums (6” pinched) 1/28 5/ to to to 6.0

High pH Action Steps  Acidify water to pH of 5.8  Switch from NO 3 - to NH 4 +  Apply an iron sulfate drench  3 lb per 100 gallons  mist solution off of foliage  Acidify water to pH of 5.1

Low pH Action Steps  Stop neutralizing alkalinity in water  Switch from NH 4 + to NO 3 -  Apply flowable limestone products:  start with 1 quart per 100 gallons  mist solution off of foliage

Monitoring EC  Set target EC ranges for crop being grown  Account for growth stages  Establishment, active growth, and bloom  Set upper and lower ranges

Plant Growth Cycle Active Growth Establishment Mature

PourThru EC’s Crops vary in requirements Crops vary in requirements Low: mS/cm Low: mS/cm  begonia, cineraria, impatiens Moderate: mS/cm Moderate: mS/cm  Easter lily, geranium, kale Heavy: mS/cm Heavy: mS/cm  chrysanthemum, poinsettia

High EC Action Steps  Decrease fertilization rate  Decrease fertilization frequency  Leach

Low EC Action Steps  Increase fertilization rate  Increase fertilization frequency

pH Drift Alkaline Water pH NH 4 + fertilizers Time “Optimum” Range

Species Effect on pH Marigold (African) pH Starting pH Species Pansy Vinca Zinnia Celosia Begonia Dianthus Tomato

The Four Most Common Mistakes 1.Adoption of a single-fertilizer formula for a given crop - Sticking to Trusting the fertilizer injector 3.Not testing soil frequently 4.Not testing the irrigation water 5.Not performing foliar analysis mid-crop.

Pre-test irrigation water and media before planting. Pre-test irrigation water and media before planting. Stock up on pH-adjusting chemicals and basic fertilizers. Stock up on pH-adjusting chemicals and basic fertilizers. Use a water test analysis to select the fertilizer and decide whether to acidify irrigation water. Use a water test analysis to select the fertilizer and decide whether to acidify irrigation water. Set up a pH, EC and nutrient monitoring program. Set up a pH, EC and nutrient monitoring program.

Testing The Foliage …