What is the pH of Fafard mix and how is it affected by plant culture?
Fafard mixes are limed so that two or three days after watering in, the pH will be between 5.5 and 6.5. However, the amount of lime in the mix is only one of several factors that affect media pH as the crop is grown. Water alkalinity level and type of fertilizer used also have a major influence on mix pH. Alkalinity, a measure of a water’s ability to neutralize acid, is caused by the bicarbonate ion. Highly alkaline waters can cause mix pH to increase over time with high levels causing a greater degree of increase than lower levels. While moderately alkaline water may not change media pH, low alkalinity can actually cause mix pH to decrease. Water alkalinity levels can easily be determined through water analysis. Fertilizer also affects media pH. Fertilizer that contain ammonium or urea (20-20-20, for example) have an acidifying effect, causing a decrease in pH after repeated use. Fertilizers that contain little or no ammonium or urea (like 20-10-20) are not strong acidifiers. Some mat
