We talk about weed issues in ponds, but another aspect of pond management is fertilization and liming. Haphazard fertilization programs are not recommended in ponds. However, liming every few years has cultural benefits to a pond and keeps the water alkalinity above 50 parts per million (ppm) which is better for certain herbicides.
When the soils become more acid, important pond nutrients like phosphorus (P) is not available to algal production. Phytoplankton are important for fish ponds for the production of oxygen. They also convert nutrients like ammonia, which can be toxic to fish, into a non-toxic form.
We spend a lot of time looking at pond weeds during the summer. When we have filamentous algae, we use compounds with copper. Copper that is toxic to plants and parasites in pond water is also toxic to catfish when the water is very soft. Copper sulfate is an example of these herbicides that is more likely to cause fish toxicity. Alkalinity needs to remain above 50ppm.
If there is no water in the pond, you can do a routine pH test on the soil. But it is not recommended to do a pH test of the water, because pH in water changes during the day. It is better to calculate the hardness of the water. UGA Extension Aquatic Specialist Dr. Gary Burtle has worked with the UGA Water lab in developing a pond water test. In my experience, if the pond has not been limed in a few years, it’s going to need lime. I’ve never seen a test come back that said no lime needed.
Sources of Lime
The real issue is solubility and particle size. Dr. Burtle says most of the lime should pass through a screen size of 200 meshes per inch. Lime larger than 60 mesh is too large; it dissolves too slow. Hydrated lime is a good lime for ponds, because it is more soluble in water than calcium carbonate.
Dr. Burtle recommends apply only 50 lbs of hydrated lime per acre in a single application in order to avoid creating ‘hot spots.’
Lime that passes through a 200 mesh, such as hydrated lime, is recommended for ponds.
Method of Application
If no water is in the pond, agriculture lime can be applied on dry pond bottom. Soil test of pH can determine the need.
With water, the worst thing we can do is dump lime in the pond from the edge. It is also not recommended to lime the perimeter of the pond. You need a boat to do it properly. Specialized equipment is also needed to calibrate correctly. Here In the top photo is Alan Dennard and Ken McKinis liming a pond a few weeks ago. They would make several passes over to not create hot spots.