Hi
I know that this article covers soilless media, so this would probably be the best place to place the info below
Posted by Dan Jacques on November 10th, 2005 12:02 pm
Maintaining a proper growing medium pH is important in achieving a high quality crop and has received a tremendous amount of attention in the horticultural press. Much of the information suggests maintaining a narrow growing medium pH range. Consequently, we often receive requests from customers requiring or “guaranteeing” growing media with a narrow pH range or specific pH when it arrives at their greenhouse/ production facilities. Acceptance or rejection of a shipment is often contingent on meeting this guaranteed pH or narrow pH range.
The use of limestone is the principle means of adjusting initial medium pH. While initial medium pH is an important aspect for the addition of lime there are also other important aspects for the addition of lime. All these factors are considered in the development of the lime source and rate used. It is very important that we help our customers understand the many purposes of adding limestone to potting media.
• Initial pH adjustment—To bring the pH of the finished product within a more suitable range for growing crops in a soilless media, most experts suggest maintaining a medium pH within 5.6—6.2 for optimal nutrient availability. Although specific recommendations vary, a pH of 5.5 to 6.5 would be considered acceptable. Dolomitic limestone is more “forgiving” in hitting a specific pH target.
• Buffering effect—The addition of lime helps to buffer the medium pH, or reduce drastic changes (rises or falls) that would occur otherwise due to the limited buffering capability of most growing media. Dolomitic limestone has been found to offer a better ‘residual” influence on buffering medium pH—a consideration often forgotten. Generally speaking, the acidic reactions of fertilization will tend to decrease the pH of a growing medium over time and the use of dolomitic limestone resists that change.
• To supply additional Calcium AND Magnesium for the duration of the crop cycle (2-3 months) time. As we all know, Mg is often lacking in a nutritional program. Dolomitic limestone contains both Calcium and Magnesium.
For the above reasons, Sun Gro has adopted the use of dolomitic limestone. Dolomitic limestone is the liming agent of choice. We have found that the use of a dolomitic limestone at a consistent rate targeting a pH range (rather than a specific pH) is the best all-around means of getting a crop started on the right track.
Sun Gro formulates growing media products to fall within a targeted pH range after being “wet out”, which means the mix has been moistened sufficiently to assure that the lime reaction will proceed efficiently. Even after “wet out” the medium pH typically takes at least two days to stabilize from the limestone addition alone and may take up to 2 weeks to be fully reacted. But why is that?
For dolomitic limestone to “react” and adjust growing medium pH, three criteria need to be met: proper moisture, time and temperature.
• Moisture content—Mixes are produced at 35-50% moisturemoisture does affect solubility of lime. Limestone must be solubilized in order to “react”. The moisture content of unused growing media is usually not high enough for the liming reaction to come to full stabilization.
• Time of delivery—It takes a period of 2-3 weeks after production for pH to completely stabilize under typical greenhouse growing conditions. Delivery of products in relation to time of production vary, therefore it is difficult to predict pH levels at time of delivery.
• Temperature—Product may be exposed to freezing temperatures in transit which will affect the lime reactivity and it’s ability to increase pH.
This means that growers who make decisions on the pH of unused growing medium are making decisions on media where the liming reaction in many cases has not come to “reasonable completion”.
There are many points that need to be considered when attempting to assure a proper medium pH range— Considerations that Sun Gro employs and monitors during formulating and producing our growing medium products…
We have conducted extensive research to determine the best rate and particle size of dolomitic limestone to adjust pH over time, while providing adequate Ca and Mg and buffering capacity for the duration of the crop cycle.
• Lime is routinely inspected when it is received and before use in growing media.
• We have several checks and balances in our production facilities to ensure that the quantity of lime added to the media is accurate and consistent.
• Dosage and run rates are recorded for each product run and kept on file for review by the quality control coordinator, production manager and technical specialists.
There are two more things that need to be considered. Firstly, how you measure pH. The method of pH measurement has a profound effect on the pH reading of a mix. This is a well-known and documented fact. Sun Gro employs the 2:1 distilled water to soil method of preparing mixes for pH measurement using state-of-the-art and well accepted pH measuring equipment. Deviating from this method invariable causes differing pH readings which then may lead to the incorrect disposition on the suitability of a mix. Secondly, and almost as significant, the irrigation solution applied to the crop affects the medium pH and often has the primary effect on medium pH. Growers need to be aware of the influence their fertilization program has on the medium pH before arbitrarily judging where the pH of an unused medium needs to be. Logically, the most reasonable way to assess the suitability of a growing medium is to wet out the mix with the irrigation solution to be used and measure medium pH using a standard method after 2 to 3 days.
The question asked in many cases is if the lime source or rate can be tailored to their particular situation. Sun Gro can offer the customer reduced or increased lime mixes: however, the grower should understand that there will not likely be a great rise or fall in pH with increased lime addition and a lower buffering effect on pH with a decrease in lime addition.
It is our general recommendation that growers adjust their fertility regime (including water quality control) rather than the lime rate in the mix. Only when the grower is unable to adjust their fertility regime to control pH should there be a change in the lime rate.
~SunGrow Technical Team
I know that this article covers soilless media, so this would probably be the best place to place the info below
Posted by Dan Jacques on November 10th, 2005 12:02 pm
Maintaining a proper growing medium pH is important in achieving a high quality crop and has received a tremendous amount of attention in the horticultural press. Much of the information suggests maintaining a narrow growing medium pH range. Consequently, we often receive requests from customers requiring or “guaranteeing” growing media with a narrow pH range or specific pH when it arrives at their greenhouse/ production facilities. Acceptance or rejection of a shipment is often contingent on meeting this guaranteed pH or narrow pH range.
The use of limestone is the principle means of adjusting initial medium pH. While initial medium pH is an important aspect for the addition of lime there are also other important aspects for the addition of lime. All these factors are considered in the development of the lime source and rate used. It is very important that we help our customers understand the many purposes of adding limestone to potting media.
• Initial pH adjustment—To bring the pH of the finished product within a more suitable range for growing crops in a soilless media, most experts suggest maintaining a medium pH within 5.6—6.2 for optimal nutrient availability. Although specific recommendations vary, a pH of 5.5 to 6.5 would be considered acceptable. Dolomitic limestone is more “forgiving” in hitting a specific pH target.
• Buffering effect—The addition of lime helps to buffer the medium pH, or reduce drastic changes (rises or falls) that would occur otherwise due to the limited buffering capability of most growing media. Dolomitic limestone has been found to offer a better ‘residual” influence on buffering medium pH—a consideration often forgotten. Generally speaking, the acidic reactions of fertilization will tend to decrease the pH of a growing medium over time and the use of dolomitic limestone resists that change.
• To supply additional Calcium AND Magnesium for the duration of the crop cycle (2-3 months) time. As we all know, Mg is often lacking in a nutritional program. Dolomitic limestone contains both Calcium and Magnesium.
For the above reasons, Sun Gro has adopted the use of dolomitic limestone. Dolomitic limestone is the liming agent of choice. We have found that the use of a dolomitic limestone at a consistent rate targeting a pH range (rather than a specific pH) is the best all-around means of getting a crop started on the right track.
Sun Gro formulates growing media products to fall within a targeted pH range after being “wet out”, which means the mix has been moistened sufficiently to assure that the lime reaction will proceed efficiently. Even after “wet out” the medium pH typically takes at least two days to stabilize from the limestone addition alone and may take up to 2 weeks to be fully reacted. But why is that?
For dolomitic limestone to “react” and adjust growing medium pH, three criteria need to be met: proper moisture, time and temperature.
• Moisture content—Mixes are produced at 35-50% moisturemoisture does affect solubility of lime. Limestone must be solubilized in order to “react”. The moisture content of unused growing media is usually not high enough for the liming reaction to come to full stabilization.
• Time of delivery—It takes a period of 2-3 weeks after production for pH to completely stabilize under typical greenhouse growing conditions. Delivery of products in relation to time of production vary, therefore it is difficult to predict pH levels at time of delivery.
• Temperature—Product may be exposed to freezing temperatures in transit which will affect the lime reactivity and it’s ability to increase pH.
This means that growers who make decisions on the pH of unused growing medium are making decisions on media where the liming reaction in many cases has not come to “reasonable completion”.
There are many points that need to be considered when attempting to assure a proper medium pH range— Considerations that Sun Gro employs and monitors during formulating and producing our growing medium products…
We have conducted extensive research to determine the best rate and particle size of dolomitic limestone to adjust pH over time, while providing adequate Ca and Mg and buffering capacity for the duration of the crop cycle.
• Lime is routinely inspected when it is received and before use in growing media.
• We have several checks and balances in our production facilities to ensure that the quantity of lime added to the media is accurate and consistent.
• Dosage and run rates are recorded for each product run and kept on file for review by the quality control coordinator, production manager and technical specialists.
There are two more things that need to be considered. Firstly, how you measure pH. The method of pH measurement has a profound effect on the pH reading of a mix. This is a well-known and documented fact. Sun Gro employs the 2:1 distilled water to soil method of preparing mixes for pH measurement using state-of-the-art and well accepted pH measuring equipment. Deviating from this method invariable causes differing pH readings which then may lead to the incorrect disposition on the suitability of a mix. Secondly, and almost as significant, the irrigation solution applied to the crop affects the medium pH and often has the primary effect on medium pH. Growers need to be aware of the influence their fertilization program has on the medium pH before arbitrarily judging where the pH of an unused medium needs to be. Logically, the most reasonable way to assess the suitability of a growing medium is to wet out the mix with the irrigation solution to be used and measure medium pH using a standard method after 2 to 3 days.
The question asked in many cases is if the lime source or rate can be tailored to their particular situation. Sun Gro can offer the customer reduced or increased lime mixes: however, the grower should understand that there will not likely be a great rise or fall in pH with increased lime addition and a lower buffering effect on pH with a decrease in lime addition.
It is our general recommendation that growers adjust their fertility regime (including water quality control) rather than the lime rate in the mix. Only when the grower is unable to adjust their fertility regime to control pH should there be a change in the lime rate.
~SunGrow Technical Team
