A need for feed

Insufficient fertilization can lead to several problems both during and after liner production. First and most straightforward, insufficient nutrients (and principally nitrogen) results in slow growth and underdeveloped liners, delaying crop time and/or resulting in poor quality liners. Low fertilizer concentrations also mean low concentrations of each individual nutrient in the fertilizer.

When insufficient fertilization results in low amounts of calcium and boron being provided to plants, young leaves and shoot tips may not develop properly — an issue exacerbated by the high humidity (and potentially low light intensities) common in propagation environments. Also, interveinal chlorosis may develop for those crops with a higher micronutrient requirement with insufficient iron or manganese being provided to cuttings.

While we could go on, these are some of the more common problems you may encounter when cuttings are under-fertilized during propagation. So, how can you avoid them?

Developing a fertilizer program for rooting cuttings is essential for success. There are a several ways to provide nutrients to cuttings during propagation.

First, water-soluble fertilizers (WSF) can be applied through irrigation as needed throughout propagation. Nutrients can also be applied overhead, with booms or below, if flooding is an option. However, all three of these methods require an irrigation event to apply fertilizer, and with no roots and frequent misting, little irrigation may be needed for the first part of propagation.

A great option for getting nutrients delivered to plants early in propagation is to apply nutrients through the mist applied to cuttings. Nutrient-enriched mist will land on leaves and the substrate surface, allowing for multiple sites of uptake. When using mist to apply WSF, be sure to use a lower concentration of fertilizer compared to concentrations used for delivery in irrigation, since the mist is applied so frequently.

Additionally, be sure to check the substrate electrical conductivity (EC) to ensure excessive fertilizer salts aren’t building up from frequent misting with fertilizer. Maintaining a sufficient leaching fraction from irrigating cuttings, or periodic clear-water leaches, can help keep the EC down.

In addition to how nutrients are applied, you need to consider how much and what type of fertilizer via analysis. The concentration of fertilizer applied to cuttings varies throughout propagation.

When cuttings are callusing in stage 2, concentrations around 50 ppm N can be appropriate. As the cuttings enter stage 3 (root development) and stage 4 (toning), fertilizer concentrations can be increased. This increasing fertilizer concentration correlates to increasing growth rates of roots and shoots, as well as increasing light intensity and temperature in the growing environment. Right at the end of Stage 4, the fertilization can be decreased prior to boxing and shipping actively growing cuttings.

With respect to fertilizer formulations, you will want to try and match the rootzone requirements of different crops with the potential acidity or basicity of fertilizers. Just like seedling plug producers, fertilizers low in phosphorous can be very useful in eliminating unwanted stem stretch and subsequent plant growth retardant applications.

Finally, and especially for low-pH (or micronutrient inefficient) crops, select fertilizers that have a higher concentration of micronutrient relative to nitrogen. This ensures that even though lower concentrations of fertilizer may be applied during propagation, sufficient macronutrients are still being provided.

When thinking about fertilizing cuttings, it should come as no surprise that there is a focus on WSF. They can be easily applied through mist, hoses, subirrigation, etc. This makes them amendable to many different production scenarios.

But controlled-release fertilizers (CRF) are also an option for fertilizing cuttings. This may seem odd or even counter-intuitive at first. After all, how can CRF provide nutrients to plants without roots to take them up? Surprisingly, cuttings are able to absorb nutrients at the base of the cutting. As root development continues into substrate, additional nutrient uptake occurs.

There are several benefits to using CRFs during propagation. First, you can reduce the amount of nutrient runoff from liners when compared to overhead fertilization, whether from mist or irrigation. Additionally, the ability of CRFs to consistently provide nutrients to cuttings — regardless of the growing environment — keeps feeding patterns regular.

Finally, since not all the fertilizer in CRF is released during the propagation period, the additional fertilizer can keep contributing to plant growth after transplanting into containers for finishing. Although the cost of fertilizing cuttings with CRF is more expensive on a per-tray basis compared to WSF, the increase in cost relative to the costs of production and sale price on a per tray basis make this increase negligible.

Whether you are growing for outside sales or in-house use, refining your fertilization program for rooting cuttings will not only help avoid problems during production, but it will improve liner quality for you and your customers. With a range of options for fertilizer types and application methods, a solution is sure to exist.