Fertilizing roses can often feel like a mysterious art, with conflicting advice from gardening books, product labels, and online sources. In a recent video, Jason from Fraser Valley Rose Farm dove into this topic, breaking down what professional growers—himself included—actually use to fertilize roses. His insights draw from years of experience, industry resources, and academic research, offering valuable guidance to home gardeners and enthusiasts.
The Starting Point: Practical Grower Experience
Jason’s journey into fertilizing roses began in the nursery trade, where slow-release fertilizers like 16-10-10 were a common staple. This formulation, higher in nitrogen (N) and lower in phosphorus (P) and potassium (K), provided reliable results across a range of perennials and shrubs, including roses.
These fertilizers, often marketed under brands like Osmocote and Florikan, deliver nutrients gradually over time. Jason highlights the practical appeal of these products—they’re easy to apply, effective, and widely used in ornamental horticulture. A typical formulation might include essential secondary nutrients like magnesium, sulfur, and trace micronutrients, all crucial for healthy growth.
But while this approach worked well, Jason began to question whether it was truly the best option for optimizing rose health and flowering. This led him to seek advice from seasoned rose growers and dive into horticultural research. Watch the original video where Jason explores the evidence:
Insights from the Pros: What Leading Rose Growers Recommend
One of Jason’s key references is a respected book by professional rose growers, including Jacques Ferare, who spent years working for large-scale rose producers. Their recommendation? Use any high-quality, commercially available fertilizer—such as 20-20-20 or 15-10-12—rather than relying on a specific formula. The point is flexibility; growers should choose what’s available and cost-effective in their region.
Interestingly, the book underscores the importance of secondary nutrients like iron and magnesium. A weekly liquid application of iron chelate and magnesium at 5 and 10 PPM (parts per million) respectively is advised to maintain vibrant foliage. This mirrors Jason’s experience—roses thrive when micronutrients are part of the feeding program, not just the major NPK trio.
Academic Research: What Science Says Roses Really Need
Jason also delves into academic studies that strip away the complexities of soil by testing nutrient levels in hydroponic systems. One key study identified the optimal balance of nitrogen, phosphorus, and potassium as:
- 100-150 mg/L nitrogen (N)
- 30-50 mg/L phosphorus (P)
- 100-150 mg/L potassium (K)
The trend is clear—roses perform best with higher nitrogen and potassium levels but require relatively modest amounts of phosphorus. This aligns with tissue analysis, which consistently shows that roses absorb more nitrogen and potassium than phosphorus.
Jason’s Approach: Adapting to Liquid Feed Fertilizers
Taking these findings into account, Jason shifted from slow-release granular fertilizers to liquid feeds. His current choice? A 17-5-17 water-soluble fertilizer—again reflecting the high-N, low-P, high-K ratio that research supports.
Liquid feeds offer the advantage of immediate results and the ability to adjust nutrient levels quickly based on how the plants respond. This method mirrors practices at Heirloom Roses, where growers favor liquid feeds for young plants to provide a faster nutrient uptake.
Jason also supplements with fish emulsion, a natural liquid fertilizer typically rated around 4-1-1. This organic option follows the same principle: prioritize nitrogen, maintain modest phosphorus, and supply micronutrients.
Organic vs. Conventional Fertilizer: Does It Matter?
Jason emphasizes that while organic and conventional fertilizers differ in how nutrients are delivered, the fundamental needs of roses remain unchanged. Organic fertilizers, like compost or fish emulsion, often require time and biological activity to break down and release nutrients, making them slower to act but beneficial for soil health. Conventional synthetic fertilizers, on the other hand, provide immediate nutrient availability, which can lead to faster results. The choice between the two often comes down to personal preference and gardening philosophy.
Applying This to Your Garden
If you’re growing roses in pots, Jason’s advice is straightforward—use a balanced, slow-release fertilizer with a higher nitrogen content or opt for liquid feeds that allow more control. In container gardening, potting soil lacks the natural reserves of nutrients found in the ground, so a complete feeding program is essential.
However, fertilizing roses in garden soil presents a different challenge. Most soils already contain nutrients, making it difficult to know what to add without risking imbalance. Jason strongly advocates for soil testing, but he acknowledges that not everyone will take this step.
For gardeners without a recent soil test, the safest route is to focus on organic amendments like compost, manure, and alfalfa meal. These bulk materials replenish nutrients naturally and improve soil health over time. They supply a balanced mix of nitrogen, phosphorus, potassium, and trace elements without the risk of over-fertilization.
The Risk of Over-Fertilization
While fertilization is essential for healthy roses, Jason cautions against overdoing it. Excessive nutrients can lead to lush, soft growth that is more susceptible to diseases and pests. Managing fertilization on the “lean” side—providing just enough nutrients to support steady growth without encouraging excessive foliage—helps reduce these risks. It’s a delicate balance, but erring on the side of caution can lead to healthier, more resilient plants.
Why Are “Rose Fertilizers” Different?
A key question Jason addresses is why many fertilizers marketed specifically for roses feature inflated phosphorus levels—sometimes triple the amount of nitrogen. Despite mounting research suggesting roses don’t need such high phosphorus, the myth that phosphorus promotes bigger blooms persists.
Jason explains that fertilizer companies cater to consumer expectations. Gardeners often look for a “magic ingredient,” and high-phosphorus formulas seem to promise spectacular flowers. In reality, excessive phosphorus can harm plants by locking out other essential nutrients like calcium and magnesium.
Key Takeaways
Jason’s recommendations reflect a growing consensus in horticultural science: focus on nitrogen and potassium for vigorous growth and flowering, keep phosphorus levels moderate, and ensure secondary nutrients like magnesium and iron are part of the mix.
For home gardeners, the takeaway is simple—don’t get caught up in fertilizer marketing hype. Trust the data, observe your plants, and adjust as needed. Roses, like all plants, thrive on balanced nutrition grounded in evidence, not outdated gardening folklore.
Jason is the owner of Fraser Valley Rose Farm, a nursery in British Columbia specializing in roses and perennials. Through his YouTube channel and website, he shares practical advice on gardening and plant propagation, helping gardeners grow thriving plants and better understand rose care.
