Fertilizers are very misunderstood by gardeners and for good reasons. Most books and videos repeat myths about fertilizers and manufacturers create even more myths in order to sell products you don’t need. Even experts, like plant societies, provide the wrong information about fertilizer.
I have assembled 10 of the biggest fertilizer myths in this post and once you understand them better you will save money.
The Term Fertilizer
I use the term to refer to both synthetic and organic fertilizer. Both add nutrients to soil and help feed plants, so both are fertilizers. When I am referring to only one group or the other I will be specific.
I wish gardeners would follow this rule to make their writings clearer.
Myth #1: Plant Specific Fertilizer
Plant specific fertilizers are things like rose fertilizer, tomato fertilizer, orchid fertilizer, African violet fertilizer and so one. A lot of gardening information will provide the “right” NPK for a specific plant. There is no such thing as plant specific fertilizer, except in the minds of marketing people and in the minds of the gardeners who they have convinced.
Here is a simple test you can do to confirm this. Google for images of a specific plant fertilizers. I have done that for roses.
These are all so-called rose fertilizers made by experts in the fertilizer industry. If you look at the one in the top left corner, it has an NPK of 6-12-16, which tells us that roses need a lot of potassium. The one in the bottom right corner is a 4-6-2. This manufacturer believes roses need very little potassium compared to N and P. The one in the middle is a 14-12-11, essentially what gardeners incorrectly call a balanced fertilizer. So roses need equal amounts of each nutrient?
How can all these experts sell the best rose fertilizer when they are all different formulations? They can’t. At most, one is right, and the others are wrong. But in fact they are all wrong. There is no such thing as rose fertilizer. Most plants use nutrients in a ratio of 3-1-2. This is true for roses, cabbages and orchids. Fast growing plants use more nutrients than slow growing plants, but the ratio remains about the same.
Myth #2: You Fertilize To Feeds Plants
We don’t feed plants in the way that we feed ourselves or our pets. Plants take the nutrient they need from the soil. They don’t gobble up the fertilizer you just put on the soil.
Our job as gardeners is to replace the missing nutrients in soil. If nothing is missing – there is no need to fertilize.
This might seem like simple semantics – do we feed plants or replace missing nutrients, but the difference in these two statements has a huge impact in how and what we use to fertilize. If soil is missing nitrogen we need to add nitrogen for growing roses or any other plant. If the soil is deficient in potassium, we need to add potassium.
You replace missing nutrients in soil – you do not feed plants.
This also means you don’t need to fertilize on a regular schedule because plants are not being fed.
If you prefer to watch the video instead of reading this post, have a look at this:
Myth #3: Epsom Salts is a Good Fertilizer
This is complete nonsense which I have discussed before in Epsom Salt Myths in the Garden.
By some legal definitions Epsom salts is not even fertilizer since it only contains magnesium and sulfur, but what is most important is that unless you have a magnesium or sulfur deficiency, Epsom salts has no place in the garden. And if you do have a deficiency – there are much less expensive options.
Myth #4: Bloom Boosters Increase Flowering
Bloom boosters and bone meal both have high phosphate (P) levels and it is incorrectly believed high P will produce more flowers. It won’t. All parts of the plant need about the same amount of nutrients. Flowers do not need more phosphate.
Unless there is a phosphate deficiency in soil, and that is not common in most soil, bloom boosters and bone meal do not produce better blooms.
More details here: Bloom Boosters – Fertilizer Nonsense #5.
Myth #5: Transplant Fertilizers Work
The idea here is similar to myth #4. It is claimed that high phosphate values found in plant starters and root boosters increase root growth, but that is not true, except in soils that are phosphate deficient. Most soil in North America is not phosphate deficient.
More on this in Plant Starters and Root Boosters – Do They Work?
Myth #6: Synthetic Fertilizer Salts Harm Plants
The general public uses the word salt to refer to table salt or to the road salt used in winter, both of which are sodium chloride. Table salt is made up of sodium and chlorine atoms. Sodium is very toxic to plants and gardeners can see this if they live in cold climates. Plants that grow along the road get too much sodium from winter salting and can die. A lot of plants won’t grow along sea shores for the same reason. Chlorine is also toxic but not as toxic as sodium.
Chemists use the word salt quite differently. For them, a salt is any molecule that is made up of two or more ions. Sodium chloride (NaCl) is made up of two ions; sodium and chlorine. Ammonium nitrate (NH4NO3) is also a salt and is made up of an ammonium ion (NH4) and a nitrate ion (NO3). Potassium chloride (KCl) is common in fertilizer and is made up of a potassium ion (K) and a chlorine ion (Cl). There are hundreds of different salts.
Except for urea, fertilizers are salts. However, these salt ions are also the nutrients plants need to survive. In reasonable amounts salts do not harm plants. In fact they die without them.
Granted too much of a good thing can be harmful. Too much fertilizer on your lawn makes it go brown and the grass can die. Too much organic fertilizer like chicken manure also kills plants.
Clearly synthetic fertilizer does not harm plants when used appropriately.
Myth #7: Organic Nutrients are Better Than Synthetic Nutrients
I see this opinion a lot. Unfortunately many people have been conditioned to equate “synthetic” with ‘harmful”. That is simply not true. One of the most deadly compounds on earth is Ricin from the caster bean plant. It is natural, organic and deadly.
When synthetic fertilizer is put on soil, the water dissolves it and quickly turns it into nutrient ions ready for plants to use.
Organic fertilizer works differently. It is mostly made up of large molecules like protein, starches, lignin, DNA and chlorophyll to name a few. Proteins contain nitrogen and sulfur, but plants can’t use these until the protein decomposes. Microbes convert the large protein molecules into smaller protein chunks and then into amino acids and finally the nitrate and sulfate ions are released. Only then can plants use them.
The same process occurs with all of the large molecules. DNA releases phosphate, chlorophyll releases magnesium and nitrogen. But decomposition happens slowly – we are talking months and years, not days.
How does a synthetic nitrate ion compare to a released organic nitrate ion? They are identical. Plants can’t tell the difference and neither can laboratories. The idea that the “organic” nitrate is somehow superior is completely wrong. The nutrients produced by a bag of synthetic fertilizer and a bag of compost are identical.
Myth #8: Salts Kill Microbes
It is common to see statements like, don’t use synthetic fertilizer because it kills soil life. This is simply not true.
Microbes, animals, plants, and even humans need the same nutrients. They all need that nitrate molecule. If synthetic nitrate killed microbes it would also kill plants and us.
For more details see: Salts Don’t Kill Plants or Microbes.
Myth #9: Organic Fertilizer Is Better
Organic fertilizer is better in some situations but not because it’s organic.
Organic fertilizer tends to consist of large molecules that need to be decomposed. This results in a slow feed for several years and this is a big advantage in most gardens, but there are some exceptions. Houseplants and plants growing in containers do better with a fast feed and therefore synthetic works better. The quick feed of synthetic is also be an advantage in vegetable gardens where you want rapid growth, especially in a cold climates with a short growing season. I want tomatoes now – I can’t wait 3 years for the manure to decompose.
Organic fertilizer also adds another important ingredient: carbon. Some call this humus (which does not really exist) and others call it humic substances. The main point is that higher carbon levels in soil lead to better soil health and better soil structure. Organic fertilizer can add carbon, but synthetic doesn’t. It is this carbon that makes organic better for long gardening.
Myth #10: Foliar Feeding Works Well
Foliar feeding does work to some extent, but it has limitations. It can only provide small amounts of nutrients and therefore is not suitable for providing the macronutrients.
Another limitation is that not all nutrients move easily in plants. Some nutrients are immobile and once absorbed by the leaves they will not move to other parts of the plant. For example, calcium is immobile and calcium absorbed by leaves won’t move into fruits or roots. A calcium spray directly on fruit may allow it to absorb calcium directly.
You can find out more at Foliar Feeding – Does It Work and Should Gardeners Use It?
Bonus Myth #11: You Need to Fertilize
I grow some 3,000 different types of plants and I fertilize almost nothing. I don’t add fertilizer when I plant and I don’t fertilize years later. Remember fertilizing is all about replacing the missing nutrients and a lot of garden soil is not missing nutrients to such a level that requires replacement. In that case you don’t have to fertilize.
One exception are containers. They get watered a lot, which washes nutrients out the bottom, so they need regular fertilizer. They also don’t have any real soil to provide nutrients.
A vegetable garden might need more nutrients in short season climates. We need fast growth to get a harvest, but even there, it is important to only add the missing nutrients.
If you don’t know what is missing, add an inch or two of compost each year as a mulch and grow stuff. That will probably add enough nutrients and it adds some carbon for soil building.