A great question about a fertilizer choice came into Ask Gardenerd this week from Selena in Australia:
“I’m new to organic growing and about to embark on creating my very own garden. Was wondering if you could tell me what would be a good fertiliser for an organic garden? Thank you, Selena”
Firstly, welcome to organic gardening. If you live in a part of Australia that has a Mediterranean climate, a lot of the information on Gardenerd will help you grow successfully. Now let’s tackle your question.
Before selecting a fertilizer (or fertiliser as you Aussies spell it), it’s important to know what nutrients your soil already contains. A store-bought NPK and soil pH test will answer that question. As I often say, it’s like driving with your eyes open.
Nitrogen, Phosphorus, and Potassium are the big 3 ingredients that plants need to grow. Soil pH matters less, because it’s harder to change, but it will help inform you about what will grow best in that soil pH.
Single Nutrients vs. Blended Fertilizers
Once you know what is lacking in your soil, you can amend it accordingly. Usually I recommend starting with an organic fertilizer blend, rather than single nutrients. Most organic fertilizers have a blend of ingredients that supply a percentage of nitrogen, phosphorus and potassium – listed as 3 numbers across the front of the box/bag – like 4-3-3.
This is usually sufficient to keep veggies growing in the garden all season long, if applied monthly (or more often in containers). But if your soil is low in only one nutrient, a single-nutrient amendment might be good. Why do I usually avoid single nutrient amendments? Because most folks tend to over-apply and tip the scales out of balance. Stick to recommended application rates listed on the box/bag and you’ll be okay.
For more information on fertilizers, and the difference between fertilizer and compost (another great amendment), watch this video.
Brand names differ across continents, so I hesitate to recommend a specific brand. You can find some approved brands for Australia here as a starting point. Your local nursery will have suggestions as well. Avoid big-box stores, they often don’t carry organic options.
I hope this helps you select an organic fertilizer to get started, Selena. Keep us posted on how things go.