Key takeaways
- Leaf nitrogen levels are influenced by production system (evergreen versus deciduous), cultivar, and plant phenology, fluctuating throughout the growing season.
- Published nitrogen sufficiency ranges are a starting point, but every site will differ.
- Growers must develop their own ranges based on plant performance. Regular and consistent sampling is required to monitor trends and inform decisions.
How leaf nitrogen levels can inform fertigation decisions in blueberries.
Nitrogen is a key driver of yield in blueberries, but overapplication of fertiliser wastes money and can be detrimental to plant health and fruit quality. How can growers monitor whether their nitrogen applications are optimal?
Leaf analysis is widely used to assess nutritional status in other crops. Although it is less well established in blueberry production, growers can benefit from adding this tool to their fertigation management kit.
What is normal?
The most recent figures on leaf nitrogen levels in Southern highbush blueberries were published in 2026 by Hanna de Jesus and colleagues from the University of Florida. Their open-access paper is available online.
De Jesus and her team collated 1 902 leaf nitrogen measurements from four fertilisation trials. Their dataset includes evergreen and deciduous production systems. Samples were collected at different phenological stages from nine cultivars (Albus, Arcadia, Emerald, Endura, Farthing, Kestrel, Optimus, Sentinel, and Ventura) over five years.
The researchers generated a table of leaf nitrogen sufficiency ranges (summarised in Table 1). These are based on a statistical analysis of the distribution of values in their dataset. Values outside the sufficiency ranges are either deficient or excessive.
Comparable values can be found in guidelines published by the New South Wales Department of Primary Industries in Australia. The 2025 guidelines recommend a nitrogen sufficiency range of 1.44%–1.65%. This value is based on the 2014 Plant Analysis Handbook edited by Gretchen Bryson and Harry Mills.
The Bryson and Mills sufficiency range is similar to the 1.47%–1.77% for vegetative growth in evergreen blueberries observed by De Jesus and colleagues. Bryson and Mills’ data come from three cultivars (Cape Fear, Georgiagem, and O’Neal) sampled in summer.
Table 1. Leaf nitrogen sufficiency ranges for Southern highbush blueberries. Adapted from De Jesus et al 2026.
| System | Stage | Leaf nitrogen % | ||
| Low | Sufficient | High | ||
| Evergreen | Vegetative growth | 1.22–1.47 | 1.47–1.77 | 1.77–2.08 |
| Flower initiation | 0.93–1.26 | 1.26–1.60 | 1.60–1.93 | |
| Flowering | 0.88–1.45 | 1.45–1.99 | 1.99–2.43 | |
| Fruit development | 1.54–1.73 | 1.73–1.93 | 1.93–2.14 | |
| Deciduous | Vegetative growth | 1.16–1.48 | 1.48–1.88 | 1.88–2.33 |
| Flower initiation | 1.19–1.44 | 1.44–1.70 | 1.70–1.94 | |
| Fruit development | 1.05–1.73 | 1.73–2.40 | 2.40–2.93 | |
Practical application
The published sufficiency ranges are a good starting point, but keep in mind that they’re not correlated with fruit yields or quality. Growers who want to incorporate leaf sampling into their fertigation management must develop their own normal values based on the performance of their blocks.
What to sample
A sample usually consists of 50–60 leaves. Collect fully expanded leaves from the current season’s growth. Take them from non-fruiting branches of several representative plants.
If the goal is assessing the overall nitrogen status of the block, select leaves that appear normal. If the goal is to measure nitrogen in problem plants, prepare separate samples with leaves of abnormal and normal (control) plants.
Do not combine samples from different cultivars and submit at least one sample from each fertigation block. Where blueberries are grown in the ground, sample plants on different soil types separately.
Gather leaf samples in the morning. Bag up each sample and keep it cool, but do not freeze it. Leaf samples are perishable, so they must be delivered to the laboratory without delay.
When to sample
Leaf nitrogen levels change during the year, and the patterns differ depending on the production system and cultivar. Therefore, nitrogen levels from leaf samples collected at different months are not directly comparable.
For example, Sophie Parks, a researcher at the New South Wales Department of Primary Industries, measured leaf nitrogen in commercial and experimental blueberry plants. She reported that maximum leaf nitrogen levels (2.0%–2.7%) occurred in mid-spring, dropping to 1.6%–1.9% in summer, and reaching a minimum in mid-winter (1.2%–1.4%).
To make sense of their plants’ leaf nitrogen levels, growers should sample at regular intervals (ideally monthly) during the growing season and consider differences between rather than within years.
How to interpret the results
Leaf nitrogen levels are a single piece of the nutrition puzzle. The published sufficiency ranges can provide context, but the plant’s vigour and performance matter more. Over time, growers should build their own dataset of leaf nitrogen levels, vigour, and fruit yields and quality for all blocks.
If nitrogen levels are out of range but the plants appear normal, check that the samples were properly collected and handled before assuming the fertigation needs adjustment. Additionally, remember that results from different laboratories are not always directly comparable.
If nitrogen levels are low and the plants look stressed, the problem could be either insufficient application or insufficient uptake.
Insufficient uptake can result from supplying a suboptimal form of nitrogen, incorrect pH of the water or growth medium, too-wet or too-dry growth medium, and plant-related factors, including poor root health, poor root distribution in the growth medium, and a lack of nitrogen transport from roots to leaves.
Excessive vigour and poor berry shelf-life are signs of too-high nitrogen levels. Here, the solution will almost always be cutting back on nitrogen applications.
Leaf analysis is not the only tool to manage nitrogen. Read the interview with Jorge Duarte for an international consultant’s perspective on monitoring plants to optimise production.
References and resources
De Jesus HI et al. 2026. New leaf nitrogen sufficiency ranges for Southern highbush blueberry. HortScience 61(2) pp 367–372.
Labserve 2021. Leaf sampling for chemical analyses. Webpage.
A downloadable guideline for collecting leaf samples.
Parks S. 2021. A study of seasonal leaf nitrogen in Southern highbush blueberry grown as an evergreen crop in Australia. NSW Government. Webpage.
Parks S. 2025. Leaf analysis as a tool for managing Southern highbush blueberry crops. NSW Government. Webpage.
Philips D and Williamson JG. 2020. Nutrition and fertilization practices for Southern highbush blueberry in Florida. University of Florida. Webpage.
Acknowledgements
Thanks to the following persons for sharing their expertise:
Craig Fulton. International Technical Manager at Mountain Blue.
Dr Eugenie-Lien Louw. General Manager at Firstfruits and Technical Manager at Wasi Berries.
