Everybody tells you that plants need to be fed. Thousands of gardening books and blogs confirm the fact. Fertilizer companies certainly continue to make you feel as if you are letting your plants down if you don’t fertilize. And most nurseries try to push their products at checkout.
I have good news for you. In most garden situations, you do NOT need to fertilize.
The idea that ornamental gardens need fertilizer is a big myth.
Which Plants are We Talking About?
This post is all about plants growing in soil. It includes all ornamental plants, but does not include containers, or raised beds that do not have real soil in them.
The other exception is vegetable gardens, where some of us have a very short season, and we need high growth rates to produce something before frost comes.
It does apply to soil that contains some clay (holds nutrients) but not sandy soil which needs to be treated differently.
Why Fertilize Plants?
Before proceeding, I need to define fertilizer. In this post it includes both synthetic and organic, including things such as manure and compost. After all, they all provide the same nutrients for plants.
The idea is pretty simple. We are living and need to eat, so we feed ourselves on a regular basis. Plants are living and so it follows that they also need to be fed. This seems to make sense, but it’s wrong.
Plants do need nutrients, there is no doubt about that.
Except for oxygen, hydrogen and carbon, plants get most nutrients from the soil. The thing gardeners forget is that soil is like a big refrigerator of food. It has lots of food stored up ready for plants to use. It is not like a cupboard with empty shelves. It is more like a large restaurant walk in freezer ready for the weekend rush. It’s loaded with food.
Assume your refrigerator contains lots of apples. When you go to the store, do you buy more apples? Of course not. You already have too many.
Fertilizing is a lot like buying these apples. You should only do it if you are running out of apples.
When you fertilize you should only be adding the nutrients which are missing from soil. There is no point adding extra potassium if the soil has lots.
How do you know what the soil is missing? There are two options; (a) grow stuff and (b) get a soil test done. I prefer option (a), just grow stuff. If it grows, you do NOT have a nutrient deficiency. You can do a soil test, but they have limited value for most gardeners.
The problem with many gardeners is that they don’t do a soil test, and they don’t trust their own plants which are showing them the nutrient levels are fine. Instead they believe marketing programs, social media and many sources of gardening information.
Roses Need Special Fertilizer
If you understand and believe what I have said so far, you will know that this title is wrong – Roses don’t need special fertilizer – they probably don’t need any at all.
Google for images of rose fertilizer. I did that and found a bunch of different products, all of which are “special rose fertilizers”. I have put a collage of these together in the above image.
I even found a special fertilizer for Knock-Out Roses – wow, I didn’t realize they were that different from other roses – it is just marketing to get you to buy more stuff.
How can all of these products be a good rose fertilizer and at the same time have different formulations?
They can’t all be right. At best one formulation is correct, and the others are wrong. But even that one is probably wrong as I will explain in the next section.
The reality is that there is no such thing as rose fertilizer, or orchid fertilizer, or tomato fertilizer, except in the minds of fertilizer manufacturers, their retailers and their faithful customers – and years ago I was one of those customers.
If manufacturers can’t agree on the right NPK formulation for roses – there is certainly an issue here.
Replace Missing Nutrients in Soil
I know some of you are still not convinced. Why would you be, when so much of the world is telling you that you must fertilize. But consider this example.
You get a soil test done on your soil and it contains lots of all the required nutrients except that you are low in nitrogen.
Your gardening friend down the street also had their soil tested. They have lots of nitrogen and lots of all the other nutrients, except they lack potassium.
Should you both use the same fertilizer for your roses?
Clearly the answer is NO. You need to add nitrogen, and your friend needs to add potassium.
The reason to fertilize is to replace the nutrients missing from your soil.
You do not feed plants – you feed the soil, by adding the missing nutrients. Plants will then take what they need from the soil refrigerator.
But …. Farmers Need to Fertilize
Actually farmers DO NOT need to fertilize to grow plants. They do have to fertilize to maximize yields, grow a good sized crop and make a profit, and there is nothing wrong with a profit.
Studies have shown that for soil in both the US and England, for various crops, the added fertilizer increases yields by 40 to 60%. What that means is that without fertilizer farms would still produce about 50% of the crop they now produce.
Fertilizer is important on farms, and it is of value in home vegetable gardens, but it has very little value in a landscape garden. Most gardeners do not care about producing bigger seed heads, or bigger root systems, or taller plants.
They do want more flowers and less pest problems, but too much fertilizer can result in more green growth in place of flowers, and more soft growth that is tastier to bugs (so I am told – this may be a myth?).
Ornamental gardens are perennial and long term projects, not annual growth races to beat Mr. Winter.
My gas plant produced 20 flower stems this year, without fertilizer. Should I really fertilize in the hopes of maybe getting 22?
The Proof – Aspen Grove Gardens
I started Aspen Grove Gardens 15 years ago. No fertilizer or transplant solutions have been used. None of the ornamental beds have received fertilizer, compost or manure. The soil is not particularly rich but it does contain 40% clay. I do mulch with wood chips which decompose and add very small amounts of nutrients. Fall leaves stay in the beds, mostly where they fall. I use the cut and drop method of cleaning up the garden – what the garden produces stays in the garden.
I grow 3,000 different types of plants, and most of them grow just fine. They flower well and I have few pest issues. Do I have the biggest roses? Probably not. Do I have the most flowers on my gas plant? Maybe not. But I also do not waste valuable resources by using fertilizer and I don’t spend time hauling it around.
I am also not polluting my local rivers and lakes by having excess fertilizer run into them.
This is not an isolated case. Lots of experienced gardeners do not fertilize.
Is Soil Depleted of Nutrients?
This is a common opinion that many people share. Agriculture removes nutrients from soil every year as they harvest the crops, so nutrient levels must be getting lower?
If you are running a farm and you get soil tested, the lab will make a fertilizer recommendation based on maximizing profit. This is a critical point. The lab balances the cost of the fertilizer, with the increase in yield, and estimates the point were it still makes financial sense.
This makes a lot of sense for a production farm where profit is critical for a livelihood.
What happens when a homeowner gets soil tested? The lab tries to apply the same logic for the homeowner. How much fertilizer is needed to maximize profit? Except that in the case of an ornamental bed there is no data to do this calculation and profit has little meaning.
I have spoken to the Ontario Government and they have verbally acknowledged that they do not know how much fertilizer ornamental beds need. The same situation exists in the UK and the US. This kind of science has not been done.
Fertilizer recommendations from a lab are at best, a guess, based on agricultural experience. But the goals for agriculture and ornamental home gardens is very different.
Look at Leaves for Nutrient Deficiencies
Lots of social media memes tell you that you can do this – but it does not work. I have discussed this in Can Leaves be Used to ID Nutrient Deficiencies?
Should You Fertilize?
I like to keep gardening simple. Start by assuming your soil has all it needs. Plant stuff. If it grows, you do not have a problem so don’t fertilize.
If you have problems growing a lot of different plants, it may be a nutrient issue. Then have the soil tested and follow recommendations.
If most plants grow well, and a few don’t, it is not the soil, except for the odd plant that is very fussy about pH. Solve this by getting different plants.
Adding a bit of compost, or manure from time to time is a good idea – not for the nutrients, but the organic matter will improve soil health.
This suggestion will not apply to all soils, but most soil containing some clay and/or organic matter will hold lots of nutrients and don’t need to be fertilized.