Researchers studied blueberry plants to figure out exactly how much fertilizer they need at different times during the growing season. They tested four different fertilizer amounts—from the minimum needed to 15 times that amount—and tracked how nutrients moved through the soil and into the plants. The big discovery: blueberries need the most nutrients when fruits are getting bigger, and they use nitrogen more than other nutrients. The study also found that fertilizer works best when applied every 10 days rather than all at once, and that too much fertilizer can actually waste nutrients and harm soil health.

The Quick Take

  • What they studied: How different amounts of fertilizer affect blueberry plants and the soil they grow in, especially during different stages of growth from flowering through fruit expansion.
  • Who participated: Seven-year-old blueberry plants of the ‘Powderblue’ variety grown under controlled conditions, tested across four growth stages over a full growing season.
  • Key finding: Blueberries need the most nutrients when fruits are expanding (getting bigger), using 3 to 10 times more nitrogen, phosphorus, and potassium than in earlier growth stages. Fertilizer works best when applied every 10 days in smaller amounts rather than all at once.
  • What it means for you: If you grow blueberries, applying the right amount of fertilizer at the right time—especially during fruit growth—can help you get better harvests while using less fertilizer overall. This approach also keeps soil healthier. However, this research was done in controlled lab conditions, so real-world results may vary based on your local soil and climate.

The Research Details

Scientists grew blueberry plants and tested four different fertilizer amounts: the calculated minimum amount needed (1×), and then 5, 10, and 15 times that amount. They measured soil nutrients and plant growth every 10 days across four key growth periods: when flowers appeared, when fruits started forming, when young fruits developed, and when fruits expanded. This allowed them to see exactly when plants needed nutrients most and how quickly nutrients disappeared from the soil.

The researchers calculated the theoretical nutrient needs by looking at the plant’s leaves and how fast they were growing and making energy through photosynthesis. This gave them a scientific baseline for what ’normal’ fertilizer amounts should be. Then they tested what happened when farmers used much more or much less than this calculated amount.

Understanding the exact timing and amount of fertilizer needed helps farmers grow better crops while protecting the environment. Too much fertilizer can run off into water supplies and cause pollution, while too little means poor harvests. This research provides specific guidance for blueberry growers about when to fertilize and how much to use.

This study was published in PLoS ONE, a well-respected scientific journal. The researchers used a systematic approach, testing multiple fertilizer levels and measuring results at regular intervals. However, the study was conducted in controlled conditions with one specific blueberry variety, so results may not apply equally to all growing situations or blueberry types. The exact number of plant samples tested was not specified in the available information.

What the Results Show

When researchers applied high amounts of fertilizer, soil nutrients increased quickly—but only for about 5 days. By day 10, nutrient levels had dropped significantly, showing that nutrients were either absorbed by plants or broken down in the soil. This means farmers need to apply fertilizer every 10 days rather than once a season to keep nutrients available.

Blueberries showed a strong preference for nitrogen compared to phosphorus and potassium. Across all growth stages, plants took up much more nitrogen. During the fruit expansion stage (when berries were getting bigger), nutrient uptake skyrocketed: plants absorbed 3 to 10 times more nitrogen, 3 to 6 times more phosphorus, and 3 to 8 times more potassium compared to earlier stages.

Interestingly, the soil’s nutrient balance (the ratio of nitrogen to phosphorus to potassium) stayed relatively stable regardless of how much fertilizer was applied. This suggests that plants naturally absorb nutrients in balanced proportions, leaving behind a balanced mix of unused nutrients in the soil.

Soil organic matter (the decomposed plant material that makes soil healthy) increased slightly 5 days after fertilizer application but decreased by day 10. This pattern was especially noticeable with low fertilizer amounts. This suggests that fertilizer affects how quickly organic matter breaks down in soil, which has implications for long-term soil health.

Previous research has shown that blueberries need different nutrient amounts at different growth stages, but this study provides more precise timing and quantities. The finding that fruit expansion requires the most nutrients aligns with what scientists already knew about how plants allocate resources, but the specific amounts and the 10-day nutrient depletion cycle provide new practical guidance.

This research was conducted in controlled laboratory or greenhouse conditions with one specific blueberry variety (‘Powderblue’). Real-world growing conditions—different soil types, climates, rainfall, and blueberry varieties—may produce different results. The study doesn’t specify the exact number of plants tested. Additionally, the research focused on soil nutrient availability but didn’t measure final berry quality or yield, which are ultimately what farmers care about most.

The Bottom Line

For blueberry growers: Apply fertilizer every 10 days rather than in large single applications. Prioritize nitrogen supply, especially during the fruit expansion stage. Adjust phosphorus and potassium amounts based on growth stage rather than using the same amount year-round. Monitor soil organic matter to maintain long-term soil health. Confidence level: Moderate—these findings are scientifically sound but come from controlled conditions and should be adapted to your specific growing situation.

Commercial blueberry farmers and serious home gardeners growing blueberries will find this most useful. The research is specific to blueberries, so it may not apply to other berry crops. People growing blueberries in very different climates or soil types than where this research was conducted should consult local agricultural experts about adapting these recommendations.

Changes in soil nutrient levels happen within days (5-10 days), but improvements in plant growth and berry production would likely take weeks to months to become noticeable. Soil health improvements from better fertilizer management would develop over a full growing season or longer.

Want to Apply This Research?

  • Set a recurring reminder every 10 days during blueberry growing season to apply fertilizer. Track the amount applied and note the growth stage (flowering, fruit setting, young fruit development, or fruit expansion) to correlate fertilizer timing with plant development.
  • Instead of applying all fertilizer at the beginning of the season, switch to a 10-day fertilizer schedule. Increase nitrogen application rates during fruit expansion stages and reduce them during earlier growth stages. Log soil observations (color, texture, organic matter appearance) weekly to monitor soil health.
  • Create a seasonal chart tracking: (1) fertilizer application dates and amounts, (2) growth stage at each application, (3) visual plant health observations, (4) berry yield and quality at harvest. Compare results year-to-year to optimize your fertilizer schedule. Take soil samples annually to monitor organic matter and nutrient levels.

This research was conducted in controlled laboratory conditions with one blueberry variety and may not apply directly to all growing situations. Fertilizer recommendations should be adapted based on your local soil conditions, climate, water availability, and specific blueberry variety. Consult with your local agricultural extension office or a soil scientist before making major changes to your fertilizer program. This information is for educational purposes and should not replace professional agricultural advice for commercial farming operations.