Several years ago, I could have suggested to organic gardeners that they use dilute fish-emulsion fertilizer as a “starter”, after setting transplants into the garden. A starter fertilizer is one that is phosphorus-rich.
There would have been very little chance of error, since the only form of fish emulsion I had seen at garden centers had a nutrient balance that would promote root growth: 2-3-1. (A brand with similar nutrient balance to the one pictured below is Indian River Organics Liquid Fish Fertilizer.)
That number sequence, 2-3-1, is a short way of telling how much, as a percentage of the total product, of the three major plant nutrients are in the fertilizer. The numbers are always in the order nitrogen-phosphorus-potassium, also called N-P-K.
All fertilizer labels show the N-P-K of the product. In the example above, 2-3-1, you can see that the middle number, the phosphorus number, is higher than the other two. Using this as a starter fertilizer would be a good plan for many organic gardeners.
Now, though, some garden centers offer another version of fish emulsion fertilizer, made in a way that gives it a very different nutrient balance: 5-1-1. The one in my current “stash” is Alaska Fish Fertilizer. This product has a larger first number, the nitrogen number. Using this on newly planted transplants would be less of a good idea. Nitrogen supports/promotes leafy growth.
If plants start their new lives in the garden with a rush of nitrogen, they might not have a good enough root system, as the summer gets hotter and drier, to keep the large above-ground part supplied with water and nutrients.
The beauty of a starter fertilizer is that it helps get a good root system established before the plants develop a lot of above-ground growth.
Organic gardeners looking for a good starter fertilizer, and thinking about using fish emulsion, should check their product label to verify the nutrient balance. Most of us are going to want to use something similar to the one that shows an N-P-K of 2-3-1 on the label when we set our transplants into the garden.
When would you use the 5-1-1 version of fish fertilizer? I am using it now, on leafy greens that were planted in late winter. I have spinach and kale in the garden, and both of those crops tend to bolt (send up a flower stalk and quit making delicious leaves) when the weather gets warm. That time is coming soon.
To keep the leafy greens tender and tasty for as long into spring as I can, I will be applying the 5-1-1 Alaska product, once every ten-or-so days, as I water those crops.
For organic gardeners who are following veganic practices, a fertilizer that is fairly rich in nitrogen, to keep late winter greens growing as the spring progresses, is Nature’s Source Organic Plant Food 3-1-1. This is a seed-based product, and its odor is a lot milder than that of the fish fertilizers.
Veganic gardeners looking for a pre-mixed starter fertilizer, with more phosphorus, may be out of luck. I haven’t seen one yet, but it is possible to create your own by adding some rock phosphate to one of the seed-meal fertilizers. This is a very concentrated source of phosphorus. Follow instructions on the label to avoid applying too much of the product.