Your Extension corner: Pond need limed? Time to test is now

Published 12:57 pm Wednesday, September 5, 2012

As fall nears and temperatures decline, ponds will become clear as the green ‘bloom’ produced by pond fertilizers dies off. Of course, some pond owners may be scratching their heads wondering why their pond did not get as green this year or remained clear throughout. Now is the time to assess a pond’s need for a lime application. Although some areas of our state are blessed with naturally productive soils and waters, others require the addition of lime to increase productivity. 

The addition of lime (calcium carbonate) to naturally acidic water (pH below 6, alkalinity below 20 ppm) acts as a buffering agent, creating a more neutral water chemistry (ph = 7, alkalinity above 20 ppm). Neutral waters allow the nutrients in the pond fertilizers to increase the phytoplankton (microscopic plants) bloom which gives ponds that translucent green hue. Waters which are acidic will often remain clear no matter how much fertilizer is applied because acidic waters do not allow for nutrients to be used by microscopic organisms. That is why those who fertilize without tracking alkalinity levels in their ponds may be literally throwing money down their stand pipe!

Determining your pond’s need of lime is as easy as filling a water bottle and taking it to your county extension office for testing. These water tests are $1.00 and can provide you with the information of whether your pond needs, or will need, limed in the near future. If tests indicate that the water sample is acidic, plans to lime should be made between November-February.  Applying lime during these cooler months reduces the risk of a fish kill and provides cooler temperatures to work in. Essentially, 5 tons of lime applied per surface acre is the minimum rate to see waters buffered to a neutral state. However, the general rule is that there is no such thing as applying too much lime as the more lime that is applied the longer it will be between applications. This is good to know because the majority of cost associated with liming is in equipment and labor. It is important to note that the time between lime applications is different for every pond as it will depend on flushing rates and the pH of soils in the surrounding watershed.

Lime should ideally be applied from a barge with a trash pump that methodically and evenly washes the lime throughout the pond. Very narrow or smaller ponds, less than 1-acre, can see waters buffered by broadcasting the lime from shore and/or by placing lime on the very upstream end of the pond to be washed in with the rains. Lime costs vary by region. Lime can be shopped through county co-ops and quarry operations, be sure to ask for calcitic or dolomitic lime as other products do not dissolve correctly and alter water chemistry. For a list of private pond consultants which offer liming or for greater detail on pond liming, please call your local extension office or visit ALEARN.edu and click on the recreational fishing icon, then the ‘suppliers’  and ‘fish pond management’ tabs for a wealth of information on pond management.

If it has been several years since the last lime application, if your pond is not achieving the bloom it once was, or if it has been over a year since your pond water was tested, please bring a water sample to the St. Clair County Extension Office and we’ll be glad to provide you with an accurate test to help you to get the most out of your pond.