PondTools

Liming and fertilization

Should I lime my pond, and should I fertilize it? One water test decides both

Test total alkalinity before you buy either product. Under 20 ppm, lime the pond this fall or winter and do not fertilize, because fertilizer does little in soft, acid water. Between 20 and 50 ppm, lime is optional and still helps. Above 50 ppm, skip the lime and decide on fertilizer by a different list: a muddy, weedy, lightly fished, fed or northern pond should not be fertilized, and one that passes the list is fertilized when a Secchi disk says so.

What the extension sheets say about lime

SRAC publication 4100, Liming Ponds for Aquaculture, sets the thresholds: "If the total alkalinity of the water sample is less than 20 mg/L, the pond may benefit from liming." On the upper end, "If the alkalinity concentration is below 50 mg/L, agricultural limestone can be used to increase alkalinity and hardness. If total alkalinity is above 50 mg/L, adding agricultural limestone will not be effective." And on fertilizer: "If a pond needs lime, it will not respond well to fertilizer."

How much to add is a soil question. SRAC 4100 says the amount "depends on the chemical characteristics of the bottom sediment" and sends you to a soil lab. No sheet publishes tons by alkalinity and soil type in one grid; the published numbers are regional, and they land near two tons.

Published agricultural limestone rates for fishing ponds, per surface acre
SourceSituationRate
SRAC 471Alkalinity or hardness below 20 mg/L"Typical application rates for agricultural or dolomitic limestone are 1 to 3 tons/acre"
Alabama ExtensionCalcitic or dolomitic lime, low-alkalinity pond"At least 2 tons per acre"; a soil test result "should be considered the minimum recommended application rate"
Mississippi State P1428Red clay hills of North and Central Mississippi"usually need 2 tons of lime per acre"
Mississippi State P1428Sandy soils of South Mississippi"usually need from 2 to 3 tons of lime per acre"
Mississippi State P1428Delta; Black Belt and loess soils"generally do not need additional lime"; "need only small amounts"
Texas A&MWater-volume estimate for a filled pond"approximately 4.5 pounds of calcitic lime (calcium carbonate) to increase the alkalinity of 1-acre-foot of water 1 ppm"

Those tons assume pure calcium carbonate, and bagged lime is weaker. SRAC 4100 gives the correction: "Divide the amount of liming material recommended (tons per acre) by the product of the neutralizing value and the neutralizing efficiency (NV × NE)." With only the neutralizing value on the bag, the example is "3.0 ÷ 0.85 = 3.53 tons of limestone needed."

SRAC 4100 says "it is usually best to apply lime in fall or winter when productivity is unlikely to be affected," spread "evenly over the bottom of the pond," and that "Ponds that require lime usually need repeat treatments every 3 to 5 years," or a quarter of the dose each year. Clemson's Liming Recreational Ponds allows "four to six weeks to adjust water quality" before fertilizer. Every sheet rejects the fast limes; Mississippi State's P1428 puts it as "Do not use quicklime, hydrated lime, or other more potent liming agents!"

What the extension sheets say about fertilizer

SRAC publication 471, Fertilization of Fish Ponds, opens with "Not every pond should be fertilized." Between it, P1428 and Mississippi State's To fertilize or not to fertilize?, the reasons not to fertilize are muddy water, weeds ("Weedy ponds should never be fertilized, as the nutrients will simply stimulate the growth of more weeds"), water that is exchanged "in less than 2 weeks," alkalinity under 20 mg/L, an unbalanced fish population, light fishing, a feeding program, or simply wanting clear water. The Mississippi State article adds that once you start "you should continue fertilizing each year" and harvest more.

SRAC 471 suggested rates per application, low-hardness water (calcium hardness below 50 mg/L)
FormGradesRate per acre
Liquid11-37-0, 13-37-0, 10-34-0"1/2-1 gallon/acre"
Powder12-52-4, 12-49-6, 10-52-0"4-8 pounds/acre"
Granular0-46-0 triple superphosphate"4-8 pounds/acre"
Time-release10-52-0"25 pounds/acre"
Granular starter20-20-5, for a pond that will not bloom (P1428)"40 pounds per acre"

SRAC 471 adds "After the initial application, apply one-half of the recommended rate." The schedule runs like this: "Begin fertilizing in the spring when water temperature stabilizes above 60 °F, usually after March 15 in the southeastern United States. Make three applications of fertilizer 2 weeks apart," and after that you go by the Secchi disk: "If the reading is greater than 24 inches, the pond should be fertilized again. If the reading is between 18 and 24 inches, this is ideal. Readings below 12 inches indicate excessive phytoplankton and the pond should be watched closely for possible dissolved oxygen problems." Over a season "as many as 10 to 12 applications may be needed," and you stop "when the water temperature drops below 60 °F in the fall."

What Pond Boss owners do

The forum's reference is the Fertilization of ponds archive thread by ewest (Moderator, Hall of Fame 2014), offered with the note "you may not need any" (2014). On lime, his standard answer below 20 ppm is "at least 2 tons per acre of ag lime" (2017). His pine-belt ponds sit at 9 to 10 ppm naturally, reach 35 to 40 on a program, and slide back toward 20 in 18 to 24 months, so he re-limes at about 25 (2005). Greg Grimes (Ambassador Field Correspondent) measured the fast alternative: hydrated lime at 75 pounds per acre took alkalinity from 10 to 28 ppm in five days, and after two rains it was back to 16 (2005).

On fertilizer the forum is far more cautious than the sheets. ewest's rule is "never use the suggested fertilizer rate, most ever used was 30% of that rate, go slow" (2010). The reason is a pond he first fertilized in 1996 that went from 36 inches of visibility to 6 in a week at half the label rate and needed copper to avoid a kill (2011).

The northern rule is the forum's own. ewest's later note in the archive thread records that "Dr Dave Willis, a fishery professor and PB member, recommended not fertilizing northern fish ponds" (2023). Bill Cody (Moderator, Ambassador Field Correspondent), who manages northern ponds, says fertilization there "often leads to winterkills and nuisance bluegreen algae blooms during July and August" (2009), and Cecil Baird1 (Hall of Fame) says unless you are feeding heavily for mass production, "do not fertilize a northern pond" (2012).

The visibility target is where members disagree. Grimes holds the southern line, "Usually you want 18-24 inches of secchi disc visibility in a fertilized pond" (2005). ewest keeps his ponds between 18 and 36 inches (2008) and adds "a little fertilizer" only when the bloom browns and clears to around 30 (2010). Cody frames the split by region: Bob Lusk's roughly 24-inch target "is meant for southern fish productivity ponds" (2023).

Where the tiers differ

Three gaps matter. The sheets' fertilizer rates are starting points for a pond that has never bloomed; experienced members use a third of them. The northern no-fertilize rule has no number behind it in any sheet here, because every sheet is southern; it rests on Willis as relayed by the moderators and on Cody's winterkills, so treat it as strong experience. And the "2 tons per acre" that circulates is a rule of thumb; it matches Alabama's floor and Mississippi's regional figures, but the authoritative answer is a soil test, and the Texas water-volume formula can come out well under it (their example works out to 1,283 pounds per acre).

What to do

  1. Test a surface sample with no mud in it; a pool kit works, per SRAC 4100. Under 20 ppm, lime the pond. Between 20 and 50, lime it if you plan to fertilize. Over 50, do not lime.
  2. If liming, send a composite bottom-mud sample to your extension soil lab and take the result as the minimum, divided by the lime's neutralizing value. Spread it evenly over the whole bottom in late fall or winter and expect to repeat in 3 to 5 years. Never put quicklime or hydrated lime in a pond with fish.
  3. Wait four to six weeks after liming before any fertilizer, and retest.
  4. Go through the reasons not to fertilize honestly. If the pond is muddy, weedy, fast-flushing, lightly fished, fed, out of balance, or northern, stop here.
  5. If you go ahead, start when the water holds above 60 degrees Fahrenheit, use the low-hardness rate or less, keep granules off the mud, and read a Secchi disk every two weeks. Add fertilizer when visibility goes past 24 inches (30 if you follow ewest), stop adding at 18, watch oxygen if it drops under 12, and quit for the year once the water falls under 60 degrees Fahrenheit.

With the alkalinity number in hand, the PondTools liming calculator (also standalone) takes acres, total alkalinity, bottom soil type (sandy, loam or clay) and the lime's neutralizing value, and returns tons of the lime you can buy. The PondTools fertilization calculator (also standalone) takes acres, the product (liquid 10-34-0, water-soluble powder, 0-46-0, DAP or 20-20-5), alkalinity, a Secchi reading, and checkboxes for muddy water, weed cover and light fishing. If the water is muddy, start with the muddy water calculator.

Sources