How important is lime/fertilization for a pond?

For pond owners interested in starting a fertilization program or improving the water quality you may need to lime your pond first to raise the alkalinity and hardness levels. Alkalinity is a measure of bases in the water that help neutralize acids. Alkalinity levels should be above 20 ppm in order for a fertilization program to be effective. Liming a pond makes phosphorus more available, which is essential in phytoplankton growth. Alkalinity can be measured using a simple water quality kit or AES can provide this service for you.

There are two key water quality components we are concerned with when liming and fertilizing a pond. They are pH and alkalinity. pH is the measure of acidity and fluctuates throughout the day. As carbonic acid is formed the pH is lowered, becoming temporarily acidic. As algae use carbon dioxide for photosynthesis throughout daylight hours, the pond becomes less acidic with the decline of carbonic acid. Because of this, pond pH normally fluctuates between six and nine. pH levels below six or above ten will cause stress to the fish and possibly lead to death. The only practical way to manage severe pH changes is to increase the alkalinity of the pond by liming.

Alkalinity is the measure of bases in the water and helps neutralize acids, therefore, influencing pH. As bases react with the hydrogen ions present, they buffer pH changes. Alkalinity is also necessary for proper phytoplankton growth, therefore, good fish production. Liming a pond makes phosphorus more available for phytoplankton growth by preventing phosphorus from binding up with metals in the soil rendering it useless. If your alkalinity levels are below 20 ppm, agricultural limestone needs to be applied at a rate of four-six tons per acre. Do not use quick or slacked lime; these can result in a rapid pH change that may kill fish. In new ponds or small ponds that are easily accessible, lime can be applied using a spreader truck. For larger bodies of water, a lime barge can be used to apply lime over the entire lake bottom. When we lime, we are liming the pond bottom, not just the surface waters. Liming is not a one-time thing and will have to be reapplied every 3-4 years.

Pond Fertilization

Pond fertilization provides planktonic algae (phytoplankton) with nutrients for growth much the same as adding fertilizer to a food plot for deer. We fertilize ponds to establish phytoplankton growth (the base of the food chain) which small fish feed on and so on up the food chain. Proper fertilization increases available food throughout the food chain, thus increasing the amount of fish (pounds) the pond can support. When done properly, a fertilization program can increase the carrying capacity of a pond from 100 pounds of fish per acre to 400 pounds per acre. Fertilization alone does not grow big fish, but allows you to have more pounds of fish per acre. However, combine fertilization with a good harvest plan and you are on the road to bigger fish. Fertilization will also help deter aquatic weed growth by blocking the amount of sunlight that reaches the pond bottom.

For a fertilization program to be effective, you need to know a few things about your pond. First, is the alkalinity level above 20 ppm? If not, you need to add agricultural limestone. If the alkalinity level is above 20 ppm then you are one step closer to being a candidate for fertilization. Second, are there any aquatic weeds present in the pond? If yes, you need to eliminate the weeds or you will have disaster on your hands. Adding fertilizer to a pond with significant aquatic vegetation growth will be just like adding fuel to a fire. The weeds will soak up the nutrients from the fertilizer and before you know it you will have the largest water garden in the county.

Third, do you have too much water flowing through your pond? If you have too much water flowing through the pond (i.e. too large of a watershed, small creek flowing into pond, many springs feeding the pond, etc.) you may be wasting money by adding fertilizer. We recommend having a retention time of two weeks or more. Most drainage systems in ponds pull the surface waters off of the pond to maintain the proper water level. However, this is the water that is receiving sunlight and the water you are fertilizing, the water you want to keep in the pond. When you add fertilizer it will dissolve in the upper water column and then flow right out of the drainage pipe, which will accomplish nothing. We have had success by using a modified fertilization schedule. This is one where if weeds are not present you can start the fertilization schedule later in the growing season during times of less flow. A June-September schedule if done consistently each year may result in more phytoplankton units and this is what it’s all about. Have AES design you a fertilization schedule to best meet your demands and pond requirements. If you are not a candidate for pond fertilization, you may consider adding fish feeders to the pond to help improve the food chain.

The main reason we add fertilizer to a pond is to improve the food chain. But first, there is a side benefit to adding fertilizer to your pond and that is to help deter aquatic weed growth. All aquatic weeds need proper habitat to grow and most importantly sunlight. When you add fertilizer to a pond you are establishing a phytoplankton bloom (microscopic algae that give ponds a green color). Once the bloom is established it will help block out sunlight from reaching the pond bottom and encouraging aquatic weed growth. It is a similar to the effect when you add lake dye to the pond. However lake dye will not only block out sunlight for aquatic weeds but it will also block out the sunlight for phytoplankton in essence destroying the base of the food chain. Phytoplankton is the primary food source for all fish species (freshwater and saltwater) shortly after they hatch. Adding fertilizer to the lake can help reduce aquatic weed growth and help your fishery at the same time. Just remember fertilization is primarily done to grow fish not deter aquatic weeds. Having said this, once you start fertilizing your pond it will not mean you may not ever have aquatic weeds show up, it is fertilizer which plants love.

Once you have determined that you are a good candidate for a fertilization program, we recommend using AES 10-52-4 water soluble Trophy Grower Max fertilizer. The application rate is 4-8 lbs/acre, we recommend applying the 8 lbs in the spring to “jump start” a phytoplankton bloom then 4 lbs/acre after that. Cost is basically $50/bag for 25 lbs. So it is about $8/app/acre compared to liquid at 1.5 gals so $9/app/acre. It is also slightly cheaper, but this is not why we sell it though. For example, with liquid fertilizer for 12 acres you will need to put out 18 gallons or 216 lbs. With water soluble you would load up 48 lbs which is much faster and easier than the liquid fertilizer. Also water soluble fertilizer dissolves right in the top of the water column where it needs to go to work. Typically, ponds need to be fertilized 5-10 times a year or 40 pounds/acre will be needed for a year supply. Water soluble fertilizer is easy to apply and can be thrown along the shoreline of the pond or by slowly pouring the fertilizer throughout the pond using a small boat. You can apply the fertilizer yourself or AES can provide this service for you.

Begin fertilizing the pond when the water temperature reaches 60 degrees Fahrenheit, usually in late March and continue to fertilize until late October when the water temperature reaches below 60 degrees Fahrenheit. Check the water visibility every two weeks using a secchi disk. If the visibility is greater than 24 inches you need to add fertilizer. If the visibility is below 24 inches, do not add any fertilizer (see chart below). Also, it is very important that you do not fertilize once or twice and then stop. If the pond needs to be fertilized after you have started a fertilization program you need to add fertilizer or you will be doing more harm than good. If you have fertilized the pond, you have provided more food which increases fish recruitment (fish surviving to larger sizes). If you stop fertilizing, the fish will decline in growth (stunt) due to a sudden reduction of the food chain.

Secchi Disk Reading Management Action
Greater than 24 inches: Fertilize
18-24 inches: Good Bloom (Do nothing)
12-18 inches: Dense Bloom (Watch Closely)
Less than 12 inches: Very Dense Bloom (Aerate at night)
Less than 6 inches: Fish Kill Likely (Aerate)