Blind Wood and Branching Strategies in Apple Trees

Pomological Solutions No. 1

There is common phenomenon in many apple varieties where they develop what is known as ‘blind wood’ on developing branches, where young primary branches do not develop secondary or tertiary branches, side shoots, or fruiting spurs. This results in less vegetative growth, thereby less photosynthesis, as well as fewer fruiting branches and lower yields. In essence, they grow great leaves, but no fruit.

Several years ago, there was research into a process of using scoring or notching and high concentrations of synthetic plant growth hormones (cytokinins) to induce branching in young trees with blind wood. This strategy works, of this there is no doubt, but to date there is yet to be a natural, organic approach that comes remotely close to the results using synthetic hormones. Here is a fact sheet on the SYNTHETIC branching strategy I mentioned. https://ag.umass.edu/fruit/fact-sheets/f-140-branching-young-apple-trees-with-plant-growth-regulators

The Process. The first step in the process is to use scoring or notching¹ just above a blind bud to stimulate growth in the buds just below the notching/scoring². The effect is at least three-fold. 1) stimulate stress-related hormones to enhance fruiting wood development in the vicinity of the scoring, 2) temporarily stop the upward flow of nutrients and natural PGRs so they concentrate at the buds, and 3) reduce the number of growing points so the nutrients are simply available to fewer growing points in the tree. All three are inter-related and work together for the desired effects to take hold. NOTE: This process must take place before the vegetative buds “break” or begin growing. Ideally, this happens just as the sap flows, but before significant bud swell. The longer you wait, the less successful the activity.

After the pruning and scoring/notching, the next step is to apply a PGR containing compound that enhances the effect of the pruning or scoring, increasing the likelihood that secondary branch or side shoot/spur develop will occur. In some varieties this is an absolute necessity from when they are young since they already have a genetic tendency towards blind wood. As a branch gets older (>2 years old), the ability to reverse this blind wood situation decreases and eventually disappears altogether. And though the scoring itself will have a positive effect on branching, the addition of PGRs supercharges the processes leading to better results. It may take more than one year to gain the desired effect. The PGR is mixed with a light latex paint mixture, in large part so you can see where you treated and where you didn’t, but also to help adhere the PGR to the tree’s surface.

Maxcel, a proprietary 1.9% solution of 6-benzyladenine, a cytokinin, in used commonly in this practice by conventional apple growers. Cytokinins, to be clear, are naturally occurring PGRs that induce flowering, cell division, branching, etc. in conjunction with other PGRs like gibberellins and auxins. There’s a paper here that describes their role in horticulture in more detail. Unfortunately, there hasn’t been much research that discusses a comparable natural approach or much information on how to successfully replicate the effects of 6-BA using natural sources. Though we know that certain plants are rich in cytokinins (generally speaking), they are magnitudes lower in their content that can be manufactured in a lab. Cytokinins are produced in actively growing regions of plants and their roots³.

This fact led me to the hypothesis that using plant extracts and biostimulants could produce a weak, but viable analog (compared to 6-BA) to stimulate branching, all the while staying “natural.” Seaweed and kelp extracts especially have been on top of my list, but also the use Regalia - a plant extract of Giant Knotweed (Reynoutria sachalinensis) and its close relative Japanese knotweed (Reynoutria japonica) both of which contain significant resveratrol content. The potential to mix coconut water - also high in cytokinins - with high concentrations of seaweed/kelp extracts and Regalia, or the DIY plant extract, seems to be strong candidate for further investigation. They may also help with overall plant health and fruiting, but we just don’t have any empirical evidence or the data to back that up.

We want a natural approach to fruit growing to be simple and approachable, and seeking and testing reasonable hypothesis based on conventional approaches is our best route forward. We need to know what works in commercial agriculture and test natural, organic alternatives touching on the esoteric at times to influence but not overpower the tree’s natural tendencies. But, often times, the needed research is beyond the ability of most fruit growers to conduct - whether for cost, time or simple know-how. That’s why we’re here. Know Your Roots, in conjunction with other growers, will continue to hypothesize and work on an approach that is successful and is replicable across a wide ranch of varieties. Please let me know if you have any questions or comments regarding this approach, or if you’d like to participate in the study. We’ll report back later with our findings and progress.

1. cutting into and/or through the cambium of the shoot to reduce vascular flow of nutrients above the blind bud.

2. A heading cut just above the blind bud (or any bud for the reason) will always stimulate growth in the buds below the cut. Pruning can also be used to stimulate growth and is something we all do every year prior to the growing season.

3. I’ll do a whole piece on plant growth hormones over the next few weeks.