Garden Fertiliser Facts, Fertiliser Fiction and Fertiliser Bullshit Merge & Grow Into Gardening Myths! In this Article I’m Going To Debunk The Fertiliser Fiction From the Facts & Help You Understand Your Plants Needs.

Garden Fertiliser Myths seem to dominate the internet and it’s time the facts were provided and the garden fertiliser fiction put in the compost bin!

So let’s start with one of the fertiliser myths I see most of all.

Plants Need To Be Fed a Balanced Fertiliser

Plants need a mix of various chemical elements (yes, chemicals) to grow. They include major elements such as Nitrogen, Phosphates and Potash (NPK), plus smaller amounts of Magnesium, Calcium and Sulphur. They also need traces of numerous other elements, for example, Boron, Iron, Manganese, Copper, Zinc, Molybdenum, and Chlorine to name just a few. You might recognise many of the trace elements as being essential to human health as well. And for the NPK think about Protein, Fat and Sugars that humans and animals need.

But that’s not to say we need to add all these things in a balanced fertiliser. Many of them are already in the soil and waiting for the plant to take them. Think of it like being in your cupboard, you don’t need to shop for them.

So though plants need all these things we don’t need to necessarly add them to the soil. It depends on what is already there (in the store cupboard). So to say the fertiliser needs to be balanced just isn’t true. It’s a myth bred of misunderstanding how plants feed and what they need.

If you have added plenty of compost or animal manure (partially decomposed compost) to the soil you will have added loads of plant food. And if you have grown legumes, such as peas, beans or a leguminous green manure AND left the roots in the soil, you have added nitrogen.

Compost adds a wide range of essential plant nutrients
Compost adds a wide range of essential plant nutrients

A similar situation exists if you’ve added wood ash to the soil. In this case you’re added a lot of potash and also even more calcium carbonate which will make the soil slightly less acid. The quantities depend on the type of wood and how it was burnt.

The other factor to take into account is that not all plants need the same mix of elements or plant food. For example leafy plants need more nitrogen whilst fruit and flowers need more potash. But many of these elements may already be present in the soil.

By balanced fertilisers many people mean the same quantities of NPK. So when artificial fertilisers were first sold they contained the same quantities of NPK. Or at least the same ratio of NPK if I’m going to be technically correct. Plant food ratios can be quoted as 10:10:10 or 5:5:5, which is exactly the same plant food ratio but the former is double the strength of the latter.

But of course plants need what is lacking and so to say a balanced fertiliser is needed isn’t true. If fertiliser is needed then it only needs to replace what is missing from the soil (or what the plant can’t obtain from the soil which isn’t quite the same).

Verdict: It’s another one of those Garden Fertiliser Myths

Plants Need Special Fertilisers Eg. Tomato Fertiliser, Fuchsia Fertiliser or Leek Trench Fertiliser

Buying special fertilisers makes gardening easy So we tend to buy a tomato fertilisers for tomatoes. Almost invariably this will actually be Potassium Nitrate but it will be sold under a fancy marketing name and might have a few additives. When I grew tomatoes commercially I bought my “Pot Nitrate” in hundredweight sacks. 10,000 tomato plants take a lot of feed when grown the traditional way.

Do We Need Special Plant Specific Fertilisers
Do We Need Special Plant Specific Fertilisers

And I had done something that few gardeners do. I’d first analysed the soil and added base dressings of fertilisers sufficient to replace anything that was in low supply. Then feeding a pot nitrate solution as a liquid feed to the roots made perfect sense. In most gardening situations it will also make sense as you don’t know what is in the soil you are growing in. You will of course oversupply some elements but that’s life.

In a commercial situation where we fed tomatoes at a high rate we had a problem at the end off the year. There was a surplus of fertiliser in the soil, enough to burn the roots of the lettuce crop that was to follow. So we had to remove it. The easiest way to do this was to “flood” the soil with water. In other words wash it out of the soil. It’s a practice I’d now frown upon as contributing to chemical pollution. Just because the high “salts” we are flushing away are natural doesn’t make it good. We’ve learnt a lot since I was a commercial grower. But what we did then was backed up by science as it was then understood.

Verdict: It’s another one of those Garden Fertiliser Myths ….. but if nothing else is available and you have no soil analysis, you can use them.

Fertilisers Need the Right Plant Food Ratio

Plants need the right nutrients in the same way as we need the right nutrients. For example if we are deficient in iron we become anaemic which means we lack energy.

But that’s not so say that fertilisers need to provide every single one of those as many will be available in the soil. So, as I explain above, fertilisers don’t need to be a specific plant food ratio, Plant food ratios just explain what is in the fertiliser in exactly the same way as food packets also include an analysis of what it contains in terms of sugars, fat, protein etc.

Verdict: It’s another one of those Garden Fertiliser Myths

Compost Tea Is The Perfect Plant Food

Not really. Compost teas will vary in the nutrients they contain depending on what the compost is made from. It will always contain fewer nutrients than there compost itself and I fail to see the attraction. Far easier is to add a bit of compost to the soil around the plant. That way when you water, or not rains, the “tea” will be made right there next to the plant roots. It’s a far easier and more efficient way of getting nutrients to the plant.

Some myths say that animal manure composts shouldn’t be used to make teas. Others swear by hanging a bag of fresh animal dung in a barrel of water and using the water as the tea! The plant doesn’t know the difference between the two as it gets the same type of chemicals in the water in either case.

Verdict: It’s another one of those Garden Fertiliser Myths

Chemical Fertilisers Are Bad For Plants

I so often hear gardeners saying they don’t use chemicals in their garden and it makes me smile. And if I challenge them by saying “why not, you actually use plenty of chemicals” many will argue with me and say they never eat food containing chemicals. But of course they do consume chemicals.

We are made of up chemicals, the main one being water. Water is a chemical. And all the food and drink we consume are chemicals.

Earlier I mentioned that I used Potassium Nitrate to feed my tomatoes and when I say this I often get people telling me I shouldn’t use chemicals. But pot nitrate occurs naturally in nature. For example it has been harvested from bat guano (poo) in some countries for generations.

What people really mean when they say they don’t want chemicals in their garden is that they don’t want man-made chemicals that don’t naturally occur in nature. Things like DDT, Glyphosphate etc. But that is an entirely different thing.

The thing is the plant doesn’t know where the nutrients come from, though we do. I personally prefer to grow my crops by the No Dig method and not add any  nutrients beyond those contained in the composts I apply to the surface of the soil. But the nitrates the plant obtains from compost are chemically the same as they obtain from man made “artificial” fertilisers.

There is a rider to all of the above. Nutrient levels affect the soil microfauna and can affect the balance of bacteria and fungi. So if we change the nutrient levels we affect the microfauna and that isn’t always good news. This is a another reason I favour No Dig, it changes levels more gently and naturally. In most cases adding compost improves the numbers of beneficial microbes.

Verdict: It’s another one of those Garden Fertiliser Myths

Foliar Fertilisers Are Better Than Soil Applied Fertilisers

Though plants obtain most of the elements they need via their roots they do have the ability to absorb some via their leaves. So mankind started to use foliar feeds. The thing is it can only enter the leaves via the stomata (little tiny door like structure in the leaves that are mainly used to expel surplus water and gases). The stomata are microscopic so the amount absorbed is tiny. The rest will sit on the leaves until washed off by the next rain. The good news is that it is then available to the roots!

But not much foliar feed gets into the plant.

The second problem is the though some feed can enter the leaf, it can’t then easily move around the plant. For example calcium foliar feeds for combating Blossom End Rot are absorbed by the leaves but can’t then be transported to the fruit. Any that lands on the fruit might be slightly absorbed but we are talking minute amounts and none of it from the leaves.

There are some nutrients that are applied by farmers and professional growers as foliar feeds but they are few and it’s a highly complex process that isn’t possible to replicate easily in the garden.

Verdict: It’s another one of those Garden Fertiliser Myths

There are more Gardening Myths on the following pages

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