Last week I showed that it does not make sense matching a fertilizer formulation to a plant type. For example, a 1-2-1 fertilizer for tomatoes does not make sense. In part this is true because every manufacturer has their own recommendation. But there is a more important mistake being made by anyone who recommends a certain formulation for a specific type of plant–read on.
Filling the Fridge
Before I talk about plants I want you to think about your own shopping habits. When you go to the store to buy groceries, does the store manager tell you what you need to buy? Do they tell you that this week you need chicken, peppers and bread? No they don’t. Why not? Because they don’t know what you already have in your fridge. If you bought a lot of peppers last week, and you have lots left you don’t need to buy any this week. The store manager does not know this.
You might have used up all the bread and have a bread shortage in the house, and so this week you need to buy bread.
The important point here is that you buy the groceries that you need to restock your fridge. You buy the ones that are missing from your fridge, not some arbitrary list of groceries that the store manager might recommend.
Nutrients Missing from the Soil
Plants use nutrients from the soil. The soil is the “refrigerator” for plants. The soil contains a variety of nutrients and as long as there are plenty of each type of nutrient, the plant can grow well. When one of the nutrients runs low in the soil refrigerator, it is up to the gardener to replace that nutrient.
If you knew that nitrogen was getting low in the soil you, the gardener, would go to the store and buy some more. You want to replenish the soil refrigerator so that the plant has access to the nutrients it needs. This is no different than buying groceries for yourself.
But buying fertilizer is different. Instead of buying what your soil needs, most people go online or to a book, and the expert (ie the store manager) tells them what they need. Oh—you want to grow tomatoes, you need a 1-2-1 fertilizer. Instead of buying what you need, you buy what the expert recommends. This makes no sense for your groceries and it makes no sense for your garden!
Instead, you should go to the store and buy some nitrogen because that is what is missing from the soil refrigerator.
Let’s look at it a different way. My soil has been created over millions of years based on the degradation of limestone. As a result of this process we have lots of phosphorus in the soil. I am not unique. Much of the north-eastern North America has similar soil. We have too much phosphorus in the soil.
When we go to buy fertilizer we don’t need any more phosphorus because we already have enough.
So when the so called ‘expert’ tells us we need a 1-2-1 for our tomatoes they are wrong. We don’t need any phosphorus. We might need a 1-0-1 fertilizer, but we don’t need more phosphorus.
Fertilizer Recommendations are Wrong!
Any time an expert, who has not analyzed your soil, tells you that you need a certain fertilizer number you can be certain they are wrong. Why? Because they don’t know what your soil has or doesn’t have. They don’t know the nutrient profile of your soil.
In the same way that the grocery store manager can’t tell you what you need to replace in your fridge, a fertilizer or plant expert can’t tell you what you need to replenish in your soil, unless that expert has analyzed your soil. That means that any box of fertilizer that makes a recommendation of a certain formula is wrong–they don’t know anything about your soil. A web site or book that recommends a certain formulation of fertilizer is also wrong–they don’t know anything about your soil.
Match Fertilizer to Your Soil
When you buy fertilizer you should be buying it to replenish the nutrients that are missing from your soil. In the same way that you buy carrots this week because you have run out of them, you should only buy nitrogen if your soil is low on nitrogen. If your soil has lots of nitrogen, don’t buy any more–you have enough.
You now have a real dilemma. Since most of us don’t do a soil test, we don’t know what is missing from the soil. If we don’t know what is missing, we have no idea which fertilizer to buy.
What we do know is that buying something because the store manager says we should is stupid. Buying something because we think it is better than nothing does not make sense either. It seems obvious that we should be doing a soil test. Join me next week, in Fertilizer Nonsense #4 – Soil Tests, to see why even this suggestion has a serious problem.
1) Photo Source: Neil Conway