Nothing is more satisfying for a grower than seeing a healthy crop leave the nursery, whether it’s headed for a retail garden centre, or a landscape project. Behind that moment is months of careful management – from watering schedules, temperature fluctuations, pests, disease pressure, and nutrition. Everything needs to be carefully considered. Growing quality plants doesn’t happen by accident!
While it would be ideal to simply pot up and let the mix do all the work, most growers know that success sits somewhere between preparation and ongoing management. The closer your potting mix comes to being self-sufficient, the easier it is to produce uniform, sale-ready plants with fewer interventions along the way.
Start with the whole growing system
A well-designed potting mix should never be considered in isolation. The container plays a major role in how water and nutrients behave, which is why pots and trays are part of the equation from day one.
Key questions to work through include:
- What container type are you using? Hard-wall pots, air-prune systems, or cell trays.
- What size container will the plant finish in?
- Which plant species are you growing?
- How is irrigation applied and how frequently?
- Where are the plants being grown? Outdoors, under shade, in a polyhouse or greenhouse.
When pots, trays, irrigation, and nutrition are aligned, plants respond more predictably and losses are reduced.
Getting the physical properties right
Once the growing environment and containers are defined, the physical structure of the potting mix can be fine-tuned. This is achieved by adjusting ingredient blends such as composted pine bark, coir fibre, peat, pumice and perlite.
These components influence critical properties including:
- Air-filled porosity, which supports root respiration
- Water holding capacity, which determines how long moisture remains available
- Drainage rate, which impacts both root health and nutrient retention
Mixes that drain very freely can support excellent root systems but often require higher water and fertiliser inputs. More water-retentive blends hold nutrients longer but need careful management to avoid waterlogging. The goal is balance, especially when paired with the right pot or tray design.
Reducing nutrient loss before it happens
One of the biggest hidden costs in nursery production is nutrient leaching. Fertiliser that exits the bottom of the pot before being absorbed is not only wasted but can also create downstream issues when water is recycled. Elevated salts and algae growth in holding ponds can quickly become a management headache.
Wetting agents play an important role here. By improving water distribution through the media, they help moisture and dissolved nutrients stay in contact with root zones for longer. This increases uptake efficiency and reduces unnecessary losses.
Organic components such as humates can also contribute by improving the mix’s ability to retain key nutrients like calcium, magnesium, and potassium, making them more readily available to plants.
Designing the nutrition profile
With the physical mix sorted, attention turns to nutrition. Most modern potting mixes rely on a combination of immediate, soluble nutrition and longer-term controlled release fertiliser.
Composted pine bark, even when mature, can temporarily bind nutrients such as iron. This is why iron is often added during composting and again at blending, ensuring plants have access from the moment they are potted. Our Maxiyield High Iron starter fertiliser is a great addition when blending.
To support early establishment, fast-acting nitrogen sources are commonly included. These provide an initial boost while controlled release fertiliser takes over as the primary nutrition source.
pH management is also critical. Bark- and peat-based mixes tend to be naturally acidic, so lime is often added to lift the pH into a range better suited for plant growth. Lime also supplies calcium and magnesium, while gypsum can be used where those nutrients are required without altering pH.
Controlled release nutrition with confidence
Controlled release fertiliser is the backbone of consistent nutrition in container-grown plants. Products like Polyon are selected based on how long the crop will remain in the pot and the growing conditions it will experience.
Polyon is available in a wide range of longevities, from short-term crops through to plants that will be held for 12 months or longer. The longevity chosen directly affects daily nutrient release. Shorter longevities release more nutrients per day, while longer longevities deliver a slower, steadier supply thanks to their thicker coating.
This predictability allows growers to match nutrition to crop timing, container size, and irrigation strategy, particularly important in smaller pots and cell trays where overfeeding can happen quickly.
Polyon formulations cover the major nutrients required for plant growth, and options are available for phosphorus-sensitive species, as well as mini prill sizes designed specifically for use in propagation trays and small containers. The video here helps explain Polyon in more detail, and our blogs are worth a read too, particularly this one: Polyon for NZ Crops.
Our team frequently get fantastic feedback from growers using Polyon. Here’s what Corey from Awa Nurseries in Waimauku, Auckland had to say:
“We have recently made the switch to using Polyon as our controlled release fertiliser in our potting mix and have been experiencing more consistent, uniform crops, with longer lasting healthy green foliage.
We grow a large variety of species in a range of all sizes and have found it produces a superior crop that is ready for market a lot quicker than what we had previously had. With less top dressing or no top dressing at all.
Would be more than happy to recommend it to a fellow grower for a successful crop for this Spring.”
Corey Ronaldson – Awa Nursery Production Manager
Better inputs lead to better plants
The most successful growers take an active role in understanding what goes into their potting mixes. When you know how your mix is built, how your fertiliser behaves, and how your pots and trays influence water and nutrient movement, troubleshooting becomes easier.
At PrimeHort, we see pots, trays, growing media, and nutrition as one system, not separate components. When those pieces work together, growers gain consistency, efficiency, and better outcomes across every crop.
If you would like help developing a potting mix and nutrition programme tailored to your nursery, including the right Polyon solution, our team is here to help.
Contact us today.
