You probably don't need to apply it "every couple of weeks" but it's pretty much harmless unless you happen to have heavily sodium saturated soils.

Unless you're having extremely heavy leaching rainfalls, a lot of it probably hanging around in your raised beds for a lot longer.

The primary reason to add a fertilizer to any soil is to provide nutrients for plants that the soil cannot deliver within the growth period of the plant. A synthetic fertilizer, like a 13-13-13, applied in reasonable amounts isn't going to do any harm to the soil microbial community. But, you may be wasting money, and could be creating some long-term problems if kept up in the absence of a need.

Unless you're growing something with a high specific nutrient demand within its growing season, like corn with it's high N demand, then usually a single application of a fertilizer around the plant in it's very early growth stages is sufficient for rapidly growing annual species. Different plants have different needs - corn has high N demand, tomatoes not so much. Get to know your plants nutrient needs, and then consult some reputable reliable sources for options on how to meet those needs. There are usually many ways to assure adequate plant nutrition with synthetic fertilizers being but one option.

Only apply any fertilizer if a good, reliable soil test indicates the need because the synthetic fertilizers are sources of pollution of our water. Nitrates are found in hte drinking water and Phosporus, from fertilizer applications, are a source of the toxic algae found in our lakes and ponds. Some states, such as Michigan, have banned fertilizers containing P unless you have a soil test that shows a need for it for that reason.

Do all GARDENS leach into the ponds and streams? Can we get a handle on how likely gardens are contributing?

The Romans discovered by trial an error that 7 feet of dirt was sufficient separation between water supply lines and sewer lines, to prevent contamination of the water. So that gives some idea of how to prevent fertilizer run-off. And also, it gives some idea on how to keep nitrate fertilizer out of the ground water. We have 20 blueberry shrubs, and I give each of them a total of three tablespoons of Schultz Plant Food every year, dissolved in water. The shrubs are heavily mulched, and they are planted to minimize run-off. I don't think any of this fertilizer ends up in the storm drain.

Fertilizer runoff has been extensively studied, and the effects are real, but not simple.

The most basic consideration is, where does the water that falls on soil go? In areas where there are numerous ag field that have been drained or tiled, a lot of the water is going to be directed to drainage systems that collect and move that water often toward natural surface waters. In the Great Lakes that can become a serious issue. The same holds for residential and urban areas that collect storm water and redirect it. Again, this becomes a real and potentially serious threat for contamination of natural water systems.

For most of us the greatest potential for fertilizer runoff comes with lawn or turfgrass treatment. One of the biggest sources is spillage into streets and paved surfaces, where eventually all of it gets washed away. But on turfgrass, less isn't always better, as explained by some U. of Minn. research explained in the video linked below. While there is a strong correlation of fertilizer runoff, especially P, with amounts added, a greater threat comes from soil washing away than comes from fertilizer runoff. So barren soils and those prone to runoff errosion provide a greater threat for P contribution to runoff than does leaching from soil. A similar result was seen in a study done by the USGS in Wisconsin in 2002. In that study unfertilized wooded and swale areas contributed more P to runoff than fertilized lawn sites in nearby areas.

To protect surface waters the proper goals should be first to prevent soil erosion via runoff, and second to use fertilizer for optimal growth (which helps with 1) while not being excessive. That means add P where it is called for, but not where it isn't. Again, periodic soil tests are a good thing.

It is not appropriate compare the effects of soil filtration of sewage to fertilizer runoff unless the same contaminants are being evaluated, and usually they aren't. The major concern from sewage is bacterial contamination (e.g. coliforms), not phosphorous.

Here is a link that might be useful: University Research Dispels Fertilizer Myth

I think we should also remember that different soils have different properties with regards to fertilizer. TX's could probably apply a huge dose of fertilizer to his gumbo clay once a year and not have a problem. However if I did that in my sand, I would be polluting the ground water. And I would quickly be experiencing nutrient deficiencies. That is why I have to apply small amounts of fertilizer frequently. of course, I only apply what is needed as per a soil test.

nil - I agree. On our heavy, calcareous, alkaline clays about the only nutrient that gets depleted over the course of a few years is N. Our bigger issue with most nutrients is poor availability of those that are there because of the soil conditions. The last thing we want to add is P.

For all -- just to be clear, there are many other sources of natural water pollution other than fertilizer runoff. For nitrates and nitrites (it's a redox couple), some of the other majors are sewer and septic leaching and natural erosion. Interestingly, the USGS study I noted above (link below) found that fertilizer use did not affect nitrogen concentrations in runoff, and further that nitrite plus nitrate concentrations in runoff were generally low.

Second phosphates are not a source of algae - they only serve as a nutrient for algae as they do for tress, plants and grasses growing on land.

Finally, synthetic fertilizers are no more prone to contributing to natural waters pollution than natural/organic fertilizer sources. The reason they are so heavily implicated is because of their comparative broad use, especially in urban areas and intensive large scale ag regions. Either synthetic or "natural/organic" if misused or misapplied is equally susceptible to contributing to the contamination of natural waters. Whatever you use, use it when needed and then do so responsibly.

Here is a link that might be useful: Effects of Lawn Fertilizer on Nutrient Concentration in Runoff

I think location may play a large role in this issue but in my area - Puget Sound - it is a HUGE problem. Run-off - not just from fertilizers or chemical pesticides but grease, oil and gasoline, soaps and detergents, pet waste, even tire debris from normal wear - is a major contaminate of storm drains, groundwater, lakes and streams and eventually the Sound and other bodies of salt water.

I recall a survey done some years ago now that tested contamination levels in some 19 different streams and rivers that fed into the Puget Sound basin and all of them tested above acceptable levels for a bunch of pesticides and harmful chemicals. Almost all were attributable to either storm water run-off or homeowner use/misuse of fertilizers and pesticides. Since that time, we have made considerable progress at reducing these levels by eliminating certain pesticides, discouraging the use of weed 'n feed fertilizers, establishing rain gardens and street swales to divert and recycle run-off and to encourage the use of organic fertilizers.

Leaching into groundwater is associated with solubility and very few organic fertilizers possess any sort of water solubility - they must be processed and digested by soil organisms before they are transformed into the soluble ions that can be absorbed by plants. As this is a relatively slow process, leaching with organics is MUCH less of a concern than it is with water soluble synthetic fertilizers. It can happen when they are applied to excess and with significant rainfall but they are not the big contributor pesticides and synthetic fertilizers are.

gal - for the most part I agree with you, with an exception, or maybe it's a fine point, about organic fertilizers vs. synthetic. Apply enough of either to deliver a pound of available N for the same growing period, you have the same potential for contribution to contamination. In the end, both the organic and the synthetic fertilizers deliver the same plant nutrient. The same can be said for P and K. The particular problems with synthetics is they are more widely used and abused, and the rate at which they can become available is much faster. But if the total amount of the nutrient per time period is the same between the two, then the potential for contamination is the same.

In most areas the greatest contamination threat for any fertilizer constituent is runoff, much more so than percolation through soil to ground waters. In that sense, organic materials (e.g. compost, manures, etc.) that are subject to capture and movement in runoff drainage pose a significant threat as they will typically decompose once in the water system. In that sense they are no better. In fact Michigan State University identifies the major sources of nitrate pollution in drinking water as "municipal and industrial wastewaters, refuse dumps, animal feed lots, and septic systems". Fertilizers don't even make the list, but feed lots (manures) and sewage outflow do.

Personally, I favor organic fertilizers as much as I can because of the other benefits they bring to soils. But as far as contamination potential goes via runoff or leaching, they are no better or worse if applied at levels that deliver equivalent nutrient amounts in the same time.

This post was edited by TXEB on Fri, Jul 5, 13 at 22:17

My biggest concern was that the synthetic fertilizers could kill the beneficial microbes of the compost. That would defeat my whole purpose of using compost and making vermacompost tea. If I understand the first few responses, I need not worry. Thank you.

Actually, the synthetic fertilizer. if used in small amounts. will benefit the microbes.

Elbourne - used in moderate amounts, no problem. The biggest issue would be from a high salt concentration, but I doubt that's an issue in your situation.

I understand where Elbourne is coming from concerning 'killing' the SFW. It wasn't long ago that on these very forums that posters talked about 'dead' soil and killing the life in the soil. I believe that some voices of moderation have cooled that talk to a more reasonable level.

Wayne, Indiana restricts the use of fertilizers containing Phosphorus just as Michigan does and for the same reasons.

kimm - unless it has happened very recently, IN hasn't yet restricted P in fertilizers.

At least 11 states have fertilizer phosphorous restrictions: Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New York, Vermont, Virginia, Washington, and Wisconsin.

In addition, the are some local county restrictions and there have been a number of municipal restrictions.

In Indiana there was legislation introduced in 2011 to similarly limit or restrict fertilizer phosphorous, but from what I can see it hasn't happened yet in that state. Steuben County attempted a county ban, but it was tossed by the IN State chemist.

Interestingly, the states that restrict or ban P in mineral fertilizers typically don't impose limitations of the use of manures, which in some areas (e.g., Chesapeake Bay) is a greater source of both P and N contamination.

As I asked above, on this forum i am interested mainly on how much pollution gets into ponds and rivers from Gardens...not fields and lawns.

wayne - is that a rhetorical question, or are your serious in your quest for an answer about how much from "gardens", whatever you mean by the term?

Tex, I think it is fair to say that this forum is dedicated mostly to home gardens. I am not talking about front yard and roadside plantings So, if talk turns to pollution and blame, I think I would like to hear how and where home gardens rate as a part of the problem.

Gardens are home food growing operations in my question.

I once had a started compost pile with not enough greens in it that wouldn't heat up. After some thought, I added some water soluble, "chemical" N fert. to the pile by dissolving the fert. in water and adding the solution to the compost pile. In no time flat that pile heated right up. The fert. was either urea or ammonium sulfate, could have been miracle grow, I don't remember.

Needless to say, the added N got that pile to go through to completion and most certainly didn't kill the organisms responsible for doing the composting.

wayne - to your question, in the grand scheme of things, gardens for home food production are no doubt a small part of the total issue.

To your original question,"Do all GARDENS leach into the ponds and streams?", the short answer is, most likely do. All water applied to a "garden" either as natural rainfall or as supplemental irrigation, goes either to plant absorption, evaporation, runoff, or leaching to greater soil depths. In typical situations there will be varying amounts to all four. A study done by USDA in Lincoln Nebraska on the relative contributions of leaching vs. runoff to the Nebraska Wagon Train watershed found that runoff volume was ~ 4X that of leaching (ref "Loss of Nitrate Nitrogen by Runoff and Leaching for Agricultural Watersheds" , M. A. Elrashidi, et al , 2005). However, that same study found that leaching actually carried a higher total amount of nitrate into watershed waters than did runoff.

But I'm not sure how that is relevant. As I read it, the initial comment that sparked the ensuing discussion, including your original question, was aimed at best practices for long-term sustainability. Whether home gardens contribute 1% or 51%, the interest is in eliminating, or at least minimizing, and adverse impact to the broader environment.

As far as this forum, I would disagree that it "is dedicated mostly to home gardens" if gardens is as you define it -- home food production. Of the questions and discussions that occur about soils, many are about permanent landscapes, turfgrass, and horticulture other than home food growing.

A web search for "Phosphorus migrating to lakes" resulted in over 1,000,000 links about the subject, one of which I have posted below. Any one with even some interest in this subject should have no problem finding out about it since there has been much reported over the last 20 years.

Here is a link that might be useful: Phosphorus migrating to lakes

Elbourne - " Every couple of weeks I have been spreading some around. The garden looks good, but I can't shake a lingering guilt. Am I doing something wrong?"

As a general practice, don't add anything to a garden until you are SURE there is a problem, and sure what the fix is. "Just in case" is almost always a waste of time and money.

When someone tells you to apply something (anything besides compost, water or mulch) to your garden, ask them what they see in the garden that indicates there is a problem, what that problem is, and how they know that __whatever__ is the solution. It usually shuts them up.

Is this one of those cases where an either/ or is better than a both/ and? I am wondering if the chemical fertilizers are killing the microbes of the compost and vermacompost tea. You would have to apply really large amounts of fertilizer to damage the soil bacteria.

I'd stop fertilizing and see what happens. Unless you have really craptastical dirt, just using compost mixed with native dirt grows good home vegetables.

kimm - the reference you cited about leaching of P into an underground aquifer on Cape Cod is especially interesting.

First is dispels the long held notion that P is soil bound and doesn't leach/percolate into underground waters. In this situation the P came from prolonged sewage discharge, the soils are sand/gravel glacial outwash with a high percolation rate, and the aquifer is quite acidic, which keeps phosphates in a soluble form, rather than getting bound with metal ions and soil aggregates. It was established that P in these soils can be washed from contaminated sediments by uncontaminated acidic water.

I would suspect that P would become similarly mobile for leaching and percolation into underlying ground waters under similar soil and water conditions. Get the pH on the acidic side, over sandy/gravely soils with high perc rate and P will likely move down as does nitrate, and potentially become mobilized if underlying soil and water conditions are acidic. The soil source of P (or N) doesn't much matter - in the end it is the amount of phosphate (and nitrate) added or formed.

"Get the pH on the acidic side, over sandy/gravely soils with high perc rate and P will likely move down as does nitrate, and potentially become mobilized if underlying soil and water conditions are acidic. The soil source of P (or N) doesn't much matter - in the end it i"

So if those conditions are not met?

It seems that everyone must have those piles of good compost ready for even 8,000 sq. ft. gardens.

Again, I am trying to zero in on typical vegetable garden conditions.

wayne - that was a set of conditions that have been found that result in P (phosphate) leaching and percolation down into underlying groundwater. It is an unusual phenomenon with P. More broadly, it has generally been held that P is soil bound and does not move into natural waters via percolation, but rather was lost via surface soil erosion and runoff. The realization of what happened on Cape Cod changes that thinking.

In the absence of those conditions you are back to what is generally considered typical - the primary mode of P loss into natural waters is via surface runoff and soil erosion for the first 6-10 mm of soil, and the primary mode of loss of nitrate is leaching and percolation down below the root zone.

Typical veg garden conditions are widely varied, and yes, they loose both P and nitrate to the environment in the same ways. There is nothing special about veg gardens, other than the possible variation in either P or N soil pool that they might represent vs. the immediate surrounding areas.

Tex, Thank you for your reply. I live out in farmland and observe some runoff from fields. Much of that runoff in fields goes to lower ground into ponds which capture the runoff elements. Some of the other runoff dies out within the field and some of the other runoff flows through grass waterways....and some runoff actually reaches ditches which may or may not have checkdam buffers, which save soil, but might contain P in the water.

In my own gardens [and likely most other gardens], there are surrounding grass areas [buffer zones]. On much of my gardens, the soil is heavily amended and soaks up water like a sponge...so I don't see a lot of runoff.

The original poster was concerned about killing soil microbes which I think that that isn't much of a problem when fertilizer is done moderately. Yes, it might speed up microbe activity which will use up organic matter more quickly.

To the OP, I would agree with other posts that said moderate fert applications will certainly not kill your soil, but if your garden is fine there's not much need to add it. One thing I would keep in mind is that compost will add a lot of nutrients and you want to be careful that over time you don't overload with certain nutrients. P for example is fairly non-mobile once it sticks to the soil. I added compost for years to my clay soil and the P and K are high enough now that I certainly don't need any fertilizers. However it seems the nearby trees are sucking out a lot of N and my plants look sad. So I am not using 13-13-13 but rather, high N lawn fert. It's working.

Of course this all followed a lab soil test.

A lot of people will tell you to do this or that to have a good garden, but it's not necessarily so for your situation. Usually those are things they did that worked in their situation.

To grow strong and healthy plants a gardener needs a good healthy soil with the soils pH in the proper range for the plants that are growing in that garden and balanced nutrient levels. The only way to know that is with periodic soil tests. A gardener should never add "fertilizers" or other soil amendments without knowing what was in the soil first.
Other things a gardener should want to know about the soil they have is
1. How much organic matter is in that soil?
2. How well does that soil drain?
3. How well does that soil retain moisture?
4. What does that soil smell like?
5. What kind of life is in that soil?
6. What is the tilth of that soil?