Managing Greenhouse Nutrition Paul A Thomas and Bodie

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 Need to shift focus to PREVENTING problems

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

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

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

The Goal Is To Achieve A Stable Medium p. H Over Time

Alkalinity Terms Milliequivalents alkalinity 1 2 3 4 5 mg/liter or ppm Ca. CO 3 of alkalinity mg/liter or ppm bicarbonate 50 100 150 200 250 60 122 183 244 305

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

Alkalinity Ca. Mg(CO 3)2 Dolomitic limestone Ca 2+ + Mg 2+ + 2 CO 32 - 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

Hardness Calcium and magnesium are the major contributors Ä “hard water” has a high Ca and/or Mg Ä “hard water” is generally associated with high alkalinity Ä can have hard water and low alkalinity – water high in Ca. Cl 2 and/or Mg. Cl 2 v

Hardness v If you have hard water: Ä check Ca and Mg concentrations Ä if high use less lime Ä monitor p. H ! Ä check Ca : Mg ratio Ä ideal ratio is 3: 1 if expressed in meq/L Ä ideal ratio is 5: 1 if expressed in ppm

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

Poinsettia Crop 10 Weeks After Planting Media p. H (adopted from Greenhouse Grower, January 2001, p. 72) Initial media p. H = 6. 0 Water alkalinity = 320 ppm Ca. CO 3 Leaching Fraction The more water applied to the crop, the greater effect high alkalinity water will have on media p. H.

p. H v p. H affects the solubility of fertilizers, and the efficacy of pesticides and growth regulators. Ä the higher the water p. H the less soluble these materials are

Dealing With High And Low Water Alkalinity

Action Steps To Correct High Alkalinity reverse osmosis 480 Alkalinity (ppm) bicarbonate acid injection 180 acid fertilizer 120 and/or less lime none

Correcting High Alkalinity If acid injection required, use the Alkalinity Calculator found on: v www. ces. ncsu. edu/depts/hort/floriculture/s oftware/

Correcting High Alkalinity v Most commonly used acids: sulfuric, phosphoric, nitric. v Need to consider the extra phosphorus (P), nitrogen (N), or sulfur (S) in the acid when selecting fertilizer. Ø 3. 4 fl oz of 85% phosphoric acid/100 gal adds 122 ppm P to the irrigation water v If acid is changed, nutritional program needs to be re-evaluated.

Other Factors

Salinity v Total Dissolved Salts (TDS) – all salts present in the water (1 m. Mho/cm=640 ppm) Ä less than 0. 75 m. Mho /cm for plugs Ä less than 1. 0 m. Mho /cm for other greenhouse crops Ä less than 2. 0 m. Mho /cm for other nursery crops

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

Where Does The Water Come From ?

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

0 >400 360 -400 320 -360 280 -320 240 -280 200 -240 160 -200 120 -160 80 -20 40– 80 <40 Frequency % Irrigation Water Alkalinity concentrations (ppm Ca. CO 3) from Florida 25 20 15 10 5

Testing The Waters …

Testing Water Quality In-House v Range 0 -8 meq/L (0 -400 ppm alkalinity expressed as Ca. CO 3) v Accuracy 0. 4 meq/L or better v Kits from $30 for 100 tests to $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 !

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

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

Distilled Water Volumes Pot Size 4 inch 5 inch 6. 5 inch 1 Qt 4 Qt 12 Qt ml 75 75 75 100 75 150 350 oz 2. 5 3. 5 2. 5 5. 0 12. 0

Flats: Use 50 ml Distilled Water

EC Comparisons 1: 2 SME Pour. Thru Indication 0 to 0. 3 0 to 0. 8 0 to 1. 0 Very Low 0. 3 to 0. 8 to 2. 0 1. 0 to 2. 6 Low 0. 8 to 1. 3 2. 0 to 3. 5 2. 6 to 4. 6 Normal 1. 3 to 1. 8 3. 5 to 5. 0 4. 6 to 6. 5 High 1. 8 to 2. 3 5. 0 to 6. 0 6. 6 to 7. 8 Very High > 2. 3 > 6. 0 > 7. 8 Extreme

Monitoring Questions Number of samples? How often? Options?

How to Monitor Sample plants with different requirements separately Ä p. H: acidic vs basic Ä EC: high vs low Randomly select plants Select plants from interior of bench

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

Initial EC

Crop p. H Ranges

Geraniums (6” pinched) 1/28 5/01 6. 0 to 6. 6 to 6. 8 5. 8 to 6. 0

High p. H Action Steps F Acidify water to p. H of 5. 8 F Switch from NO 3 - to NH 4+ F Apply an iron sulfate drench F 3 lb per 100 gallons F mist solution off of foliage F Acidify water to p. H of 5. 1

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

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

Active Growth Mature Establishment Plant Growth Cycle

Pour. Thru EC’s Crops vary in requirements Low: 1. 0 - 2. 6 m. S/cm Ä begonia, cineraria, impatiens Moderate: 2. 0 - 3. 5 m. S/cm Ä Easter lily, geranium, kale Heavy: 2. 6 - 4. 6 m. S/cm Ä chrysanthemum, poinsettia

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

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

p. H Drift 8. 5 8. 0 7. 5 7. 0 6. 5 p. H 6. 0 5. 5 5. 0 4. 5 Alkaline Water “Optimum” Range NH 4+ fertilizers Time

Species Effect on p. H 8 7 p. H Zinnia Vinca Marigold (African) 6 Starting p. H 5 4 Pansy Begonia Celosia Dianthus Tomato Species

The Four Most Common Mistakes 1. Adoption of a single-fertilizer formula for a given crop - Sticking to 20 -20 -20 2. 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. Stock up on p. H-adjusting chemicals and basic fertilizers. Use a water test analysis to select the fertilizer and decide whether to acidify irrigation water. Set up a p. H, EC and nutrient monitoring program.

Testing The Foliage …