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  • Writer's pictureKaren Peterson

Demystifying Sap Flow Pruning – The Physiology of it All 

Sap flow pruning principles are intended to support the vine’s vascular system development and flow, and why wouldn’t you want to? The vascular system is responsible for delivering water, nutrients, and carbohydrates throughout the vine – it makes sense that you wouldn’t want to negatively impact them. 


As you recall there were 2 key questions from the last post. We’re diving deeper into the answers to these questions as they relate to sap flow pruning.


What drives vascular system development of vines?


and


How can pruning choices directly impact vascular system development?


Vascular System Development: Use it or lose it

Vegetative growth weighs heavily on the vine’s allocation of vascular tissue growth in the trunks. Vascular tissue’s job is to deliver support for developing cells and growth of the vascular system will be prioritised to support the most physiologically active tissue. If most of the vegetative growth is fed by a specific portion of the trunk, the vine will focus most of its resources and vascular tissue growth there to meet the physiological demand.


Pruning in cultivated grapevines dictates the location and demand for vascular tissue development every year (i.e. the number of buds and their location on the vine). The more restrictive your training system, the harder it can be to keep the pull of resources spread equally 360 degrees around the trunk, which can lead to unbalanced flow through the trunks as vines age. Think head trained vs single guyot. As pruning structures become more restrictive to fit a trellis systems, the allocation of vascular tissue shifts to where it is most needed. Where a head trained vine may be able to achieve growing points spread relatively equally in 360 degrees, a single guyot system is limited to 2 focused sides of the trunk, one with greater pull than the other.


grape vine trunk cross section, sap flow pruning, gentle pruning, pruning for sap flow
No growing points to support? No need for vascular tissue development (Wineaustralia.com, 2021)

In older guyot and other 2-dimensional trellis systems it is important to keep this basic principle of vascular system development in mind to ensure the desired vegetative growth is well supported. For example, in a single guyot pruned vineyard:

  • Always leave a spur on the opposite side of the trunk from the fruiting cane to ensure the vascular tissue on both sides of the trunk are in use

  • Alternate which side of the trunk the fruiting cane originates from periodically. By alternating which side of the trunk has the renewal spur, and which side has the fruiting cane periodically, the vascular demand around the trunk is evened out over the years.


It is equally, if not more, important to be thinking of how to support vascular tissue development with new plantings - regardless of the endgame pruning structure. Your pruning choices need to nurture the vascular system needed to support the mature vine you’re envisioning.


Pruning Choices – Time Does Not Heal All Wounds

During pruning we’re often cutting off over 90% of one year old wood every year – so naturally there are a few key cuts and effects that need to be addressed here: 


Die Back is Real – leave room for it

After cuts are made during winter pruning there is a certain amount of tissue that dies back (cone of desiccation) as the vine “heals” from pruning wounds. This is why it is ESSENTIAL to leave a buffer zone on your cuts.


cone of desiccation, die back, grape vine pruning, sap flow pruning
Leave a buffer! Die back, aka cone of desiccation, is part of the vine's natural healing process. Leaving space between pruning cuts and the vascular tissue you want to keep to minimises the negative impacts of pruning.(Winetwork-data.eu. 2021)

  • Pruning a spur? Leave at least 1cm+/- above the top bud 

  • Cutting last year’s fruiting cane to make room for this year’s? Do not cut right at the base of your new cane - leave 2cm+/- past the base of the new cane

  • Have a bunch of unnecessary canes in the head? Leave a nubbin and plan to manage shoot growth in this area during the season.


It’s simple, but it is surprisingly hard for many to come to terms with – particularly when talking about canes that are not destined for spurs or fruiting canes. Acknowledging that die back happens is the first step towards acceptance of what for many can look like untidy cuts that lead to unruly vines. By leaving room for the vine’s natural healing process, you’re ensuring subsequent vegetative growth has the uninterrupted vascular plumbing it needs for success. 


Note: Shoot thinning at the right time during the season can reduce unwanted future shoot growth without the same negative implications on vascular system development as removing that growth at pruning. For example, if instead of shoot thinning the head of the vine excess canes are left for removal at pruning, you’re leaving a concentrated area of pruning wounds which is not ideal - even if you leave room for tissue to die back. 


Avoid LARGE cuts – ditch the hand saws and accept a little funk in your trunk!

sap flow pruning, gentle pruning, no large pruning cuts, respectful pruning, viticulture
Large cuts intended to keep fruiting wood close to the trunk majorly disrupt sap flow and are a direct route into the trunk for diseases that can cripple vascular flow

Avoiding pruning cuts on any wood older than 2-years-old is a top principle of sap flow pruning. Large cuts, particularly those made to wood greater than 3 years old, have a greater area of dieback associated with healing, and due to the proximity to the head of the vine can seriously disrupt healthy sap flow. Not to mention these cuts create a greater area of exposure and a direct path of entry for trunk diseases to enter the vine when not properly treated. 


The principle of limiting pruning cuts to younger tissues lends itself well to healthy vascular tissue development and a more “natural” growth pattern for the vine. This is where sap flow pruning can lose some potential believers. Cultivated vines are restricted to grow within the space allocated to them both horizontally (vine spacing) and vertically (trellis height). If pruning cuts are limited to 2-year-old wood or younger, it does not take much imagination to picture fruiting wood moving further away from the trunks and pushing the limits of their designated growing area.  Good pruning practices and cane selection can greatly limit the rate at which the fruiting wood moves further away from the central trunk, but in sap flow pruning there is an accepted amount of fruiting wood migration away from the trunk/cordon. 


Note: within the dogma of sap flow pruning there is acceptance of large cuts/vine surgery, but there’s too much to unpack there for this post.


Grow with the flow – Bud Orientation

In keeping with the rest of its principles, sap flow pruning also drills down to bud orientation on canes and spurs. Whenever possible, renewal canes and renewal spurs should have basal buds positioned on the far side of the cane pointing away from the trunk. This helps ensure next year’s replacement cane or spur is in the best possible position to minimise migration of fruiting wood, but also follows the principle of directing sap flow. 


What next? How do you start and what are some of the follow up practices to help support your journey to sap flow pruning mastery?


Talk to your pruning teams and remind them of these key points:

  • Make sure there are buds (growing points) positioned to support desired sap flow and vascular tissue growth in season

  • No large cuts – stick to 2 (max 3) year old wood or younger

  • Leave a buffer zone between the cut and the wood you want to keep

  • Try for basal buds that face away from the trunk on canes and renewal spurs when possible, to direct sap flow and improve future pruning options.

  • Accept some amount of fruiting wood migration away from the trunk and make smart pruning choices to help limit this


Adoption of sap flow pruning in older vineyards:

  • It’s never* too late to start

    • Never say never - if a vine has visual symptoms of trunk disease, basic sap flow pruning principles are not going to be enough. Remedial surgery may be able to extend the life of the vine and rebuild healthy vascular system.

  • Take away the hand saws!!! I’ve seen far too many of these handed out at pruning.

    • This doesn’t mean that absolutely no large cuts are going to be made, loppers can take some big chunks out of vines. Nor does it mean no large cuts are required. What it does is it removes the urge to make unnecessary large cuts by those inexperienced in the ways of sap flow pruning.

    • If large cuts are required - e.g. vine surgery for trunk disease - this should be done under the guidance of someone familiar with vine physiology and the principles of sap flow pruning.

  • Expect pruning to take a little longer as your team hone their skills

  • Continue to protect pruning wounds with chemistry or cultural practices!

    • Sap flow pruning DOES NOT eliminate the risk of trunk disease.


In the growing season:

  • One of the best practices that can support sap flow pruning is shoot thinning – specifically in the head and around spurs.

  • When targeted in the head of the vine and around spurs, shoot thinning can help reduce the number of cut points you’ll have to make next winter. 

  • Removing green tissue during active vine growth does not have the same dieback/sap flow interruption as winter pruning cuts. 


With the pruning season starting in the Southern Hemisphere, we’re more than happy to talk about sap flow pruning with you and your team. We all know how subjective pruning can be and how helpful it is to discuss these practices in the field, so feel free to give us a call. Also check out the citations and helpful resources for some great reference material to help you get started.  


Happy Pruning!


Photo Citations and Helpful Resources:



Wineaustralia.com. 2021. Soft pruning making a big impression – at last. [online] Available at: <https://www.wineaustralia.com/news/articles/soft-pruning-making-a-big-impression-at-last> [Accessed 20 April 2024].


Comparison between Crown Head and SIMONIT&SIRCH METHOD. 12 January 2021. Free online course from Simonit&Sirch <https://simonitesirchacademy.com/en/courses/comparison-crown-head-and-simonitsirch-method/lessons/comparison-between-crown-head-and-simonitsirch-method/ >[Accesses 20 April 2024]


The “Gentle Pruning’ Method - article by Hanns-Christoph Schiefer, translated by Duncan McNeill. pdf available upon request [Accessed April 2016]

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