Episode Details

In this podcast, retired college horticulture professor Debbie Flower explains about the use of rooting hormones and fertilizers for newly-installed plants. You’ll find out:

How rooting hormones work.

How auxins (the rooting stimulant in root hormones) can either inhibit or promote growth.

Why you don’t want to use rooting hormones on an established plant or transplant.

Why you want to cut the roots of a tree or shrub before planting.

Why you don’t want to add fertilizer at planting time.

The benefits of “paper hats” on new plantings.

And if you are using kelp or seaweed products as a root stimulator, you’d be better off spending your money on water and mulch. According to the Washington State University study, “The Efficacy and Environmental Consequences of Kelp-Based Garden Products” :

“• There is no documented benefit to applying plant hormones to newly planted or established plants in gardens and landscapes. Hormones are produced naturally by the plant and transported to the tissues that require them. The two most important additions new transplants require are water and mulch.

• Good quality research on kelp- containing biostimulants has been performed by several researchers in different climatic regions using different species of woody plants in natural settings. None of them reported success:

• Roots of newly planted trees treated with biostimulants showed no improved growth compared to control trees. (Barnes and Percival 2006; Gilman 2004; Popenoe et al. 2017).

• The best performing trees and shrubs were those that were irrigated frequently for 38 weeks post installation (Gilman 2004) or received a simple topdressing of pine bark mulch immediately after planting (Figure 3; Abbey and Rathier 2005).

* Trees treated with biostimulants and assessed two years after planting were not significantly different than those receiving only water (Kelting et al. 1998).

* No biostimulant was able to confer increased protection to shrubs and trees against drought or salt damage compared to plants treated with water (Banks and Percival 2014).

* Researchers who tested biostimulants that were reported by local growers to be highly effective could find no evidence to support that belief (Popenoe et al. 2017). In fact, some of the products were worse than the controls. “

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Here’s a transcript of today’s newsletter podcast:

Farmer Fred  0:00

Ray sent us an email, to Fred at farmerfred.com. He says, "I recently bought some fruit trees, and the label mentioned using a rooting stimulant for transplanting. In further research I found that certain root stimulants are illegal in California. Do you know why?" I bet it's because there's something else in that stimulant, Ray. The stimulants themselves may not be the problem. But with more information on that, we bring in America's favorite retired college horticultural Professor, Debbie Flower, who is probably going to snuff your dreams, right?

Debbie Flower  0:35

Root stimulants typically contain, not all of them, but typically contain synthetic auxin. Auxin is a plant hormone, it's produced by the plants, produced in the buds, which is why you don't always want to remove the buds at the tip of the stem. It's produced in the buds and it controls the growth of the plant. At certain concentrations, synthetic hormones will prevent growth. At other concentrations, it will promote growth. When it's applied externally to roots, it has different and fewer effects on the plant. It's not stimulating root growth per se. It's actually subduing above groun