Potted Blueberry Fertiliser Trials

From 2019 to 2021 PlantNet® conducted fertiliser trials on blueberries and deciduous fruit trees. The aim of these trials were to help the home gardener get the best out of their PlantNet® products using products readily available to the home gardener. This page contains a summary of the blueberry fertiliser trials, with recommendations on the best fertiliser plan.

Scroll to the bottom of the page for our summary!

Artificial and organic products have shown the following results and we have found there are some fertilising plans which showed better results than others.

Fertiliser plan 1 produced the largest fruit and the most numbers of Blueberries.

PLEASE NOTE: PlantNet cannot recommend specific brands of fertiliser as there can be privacy and confidentiality issues if we do this. Please follow the directions below.

When purchasing fertilisers look for the nutrient analysis on the container to match as closely as possible to the product NPK used in our fertilising plans below. There are products available on the market with the same or similar analysis to what we have used.

Examples of products on the market and how they list nutrient analysis below.

The soluble liquid fertiliser we tested in Trial 2.

The controlled release fertiliser we tested in Trial 1.

Three different fertiliser plans were used. Apply once a fortnight for best results but every 3 weeks is fine.

Fertiliser plan 1– This has shown the best plant growth and cropping results. Use all products in the plan and apply separately and water in. Apply 1 tablespoon of controlled release fertiliser straight after planting and nothing else for 3 weeks.

Products used:

Product 1- Controlled release fertiliser with analysis of (N)Nitrogen 15.3, (P) Phosphorous 2, (K) Potassium 12.6 & has some trace elements.

Product 2- Urea (N) Nitrogen 46

Product 3- Sulphate of Potash (K) Potassium 41

Product 4- Liquid trace element mix.

Fertiliser plan 2– Produced 30% less fruit than Fertiliser plan 1 This has shown the best plant growth and cropping results. Use all products in the plan and apply separately and water in. Begin fertilising 3 weeks after planting.

Products used:

Product 1- Soluble fertiliser blend- (N)Nitrogen 14, (P) Phosphorous 2.6, (P) Potassium 21

Product 2- Gradual release fertiliser blend- (N)Nitrogen 13, (P) Phosphorous 1.0, (P) Potassium 11 Has some trace elements

Product 3- Liquid Potassium- (K) Potassium 14

Product 4- Liquid trace element mix

Fertiliser plan 3 (fully Organic) produced 60% less fruit than Fertiliser plan 2 and 80% less fruit than Fertiliser plan 1 . Use all products in the plan and apply separately and water in. Apply 1 tablespoon of controlled release fertiliser straight after planting and nothing else for 3 weeks.

Products used:

Product 1- Organic Controlled release fertiliser with analysis of (N)Nitrogen 15.3, (P) Phosphorous 2, (K) Potassium 12.6 Has some trace elements

Product 2- Natural Potash- (K) Potassium 41

Product 3- Seaweed, fish, humic acid, and manure.

Product 4- Kelp, seaweed, humic acid, and manure have been digested by the beneficial bacteria.

Fertiliser Plan 1

This plan showed the best vegetative growth and produced the best cropping result. Follow the table below for the best results from your blueberries.

Please note: Premium azalea potting mix contains controlled release fertiliser – do not add more controlled release fertiliser if using this mix until the second application OR until the fertiliser in the potting mix expires, as listed on the bag.

Fertiliser Plan 2

This plan produced 30% less fruit than Fertiliser Plan 1. The aim of this plan was to test the effectiveness of liquid fertilisers on blueberries and no controlled release fertiliser.

Please note: Premium azalea potting mix contains controlled release fertiliser – if you use this mix with Fertiliser Plan 2 you will see different results than us.

This fertiliser plan is repeated in year 2 and beyond.

Fertiliser Plan 3

This plan produced 80% less fruit than Fertiliser Plan 1. The aim of this plan was to test the effectiveness of organic products on blueberries and no controlled release fertiliser.

Please note: Premium azalea potting mix contains controlled release fertiliser – if you use this mix with Fertiliser Plan 2 you will see different results than us.

Summary

For the best results in your blueberries we recommend following Fertiliser Trial 1. The benefits of this trial aren’t only fruit production – the blueberries in this trial were healthier and more resistant to pest and disease attacks.

To follow this trial you need to stock up on:

A good controlled release fertiliser, like the one in the orange tub at the top of the page. The fertiliser you use doesn’t have to be exactly this fertiliser – what’s most important is the NPK ratio is similar.
A bag of urea (Nitrogen 46)
A bag of sulfate of potash (Potassium 41)
Trace element mix (you can purchase concentrate, ready to use, or as a soluble powder)