Why Pre-Flowering Nutrition Is Critical.

For Marlborough Sauvignon Blanc, nutrition in the weeks between budburst and flowering is one of the most important nutritional periods of the season.

By flowering, the vine has already made a substantial investment in shoot growth, leaves and inflorescences. At the same time, flowering and fruit set are approaching—the point at which much of the season’s yield potential becomes determined.

This is particularly important in Marlborough, where a cool climate, relatively short growing season and high-yielding Sauvignon Blanc production system place considerable demands on the vine.

Research conducted in Marlborough has demonstrated that many of the weather conditions associated with yield occur before 50% flowering, while local research has also shown that carbohydrate reserves change rapidly around flowering. (Oskar Bordeaux)

That makes pre-flowering nutrition much more than simply “feeding the vine”.

It is about ensuring the vine has the nutritional resources required to build a functional canopy, maintain reproductive development and move successfully through flowering and fruit set.

The vine changes rapidly after budburst

At budburst, the developing shoots initially rely heavily on stored reserves in the trunk and roots.

As shoots expand, the vine rapidly transitions towards current-season photosynthesis supplying an increasing proportion of its carbon requirements.

Research on Marlborough Sauvignon Blanc has shown that carbon and nitrogen reserves are highly dynamic throughout the season. In particular, root and trunk reserves change substantially as the vine progresses through early growth and flowering. (IVES)

Research on grapevines in New Zealand has also demonstrated that root non-structural carbohydrates decline after budburst and reach a minimum around flowering as resources are used to support rapid canopy development. (Wiley Online Library)

This is why the period between budburst and flowering should not be regarded simply as a period of vegetative growth.

It is a period of resource mobilisation.

The vine is simultaneously developing:

• shoots

• leaves

• inflorescences

• rachises

• tendrils

• roots

• reproductive structures.

All of these processes require carbon, nitrogen and mineral nutrients.

Why nitrogen matters before flowering

Nitrogen is particularly important during early shoot development because it is required for protein synthesis, chlorophyll formation, enzymes and cell division.

A shortage of available nitrogen during rapid spring growth can restrict leaf development and shoot growth, reducing the vine’s ability to establish an effective photosynthetic canopy.

But this does not mean that more nitrogen is better.

Marlborough’s Sauvignon Blanc vineyards can already be highly vigorous, particularly on fertile Wairau Plain soils.

Local research has shown that vineyard soil and site characteristics can have substantial effects on Sauvignon Blanc vine vigour, yield and fruit composition. Research around Dillons Point, for example, has associated the fertile soils of the area with higher yields and differences in Sauvignon Blanc wine composition. (Rural News Group)

Excessive nitrogen can therefore create a very different problem.

Too much readily available nitrogen early in the season can drive excessive shoot growth and canopy density. In a cool, humid canopy, this can increase the risk of disease and create additional canopy-management requirements.

New Zealand research has specifically highlighted the risk of excessive spring nitrogen producing dense canopies, with potential consequences for Botrytis, while excessive ammonium accumulation has also been associated with inflorescence necrosis and bunch abortion. (Rural News Group)

The objective should therefore be:

adequate nitrogen availability—not maximum nitrogen availability.

Flowering is a major nutritional transition

Flowering represents one of the most demanding stages of the early growing season.

The vine needs to maintain shoot growth while simultaneously supporting the developing inflorescences.

At this point, the nutritional status of the vine can interact with environmental conditions to influence fruit set.

This is especially relevant in Marlborough.

A long-term study involving four commercial Marlborough Sauvignon Blanc vineyards found that the critical periods associated with yield components occurred predominantly before 50% flowering, both in the previous season during inflorescence initiation and during the current season. (Oeno One)

This is a significant finding.

It means that by the time a grower sees poor fruit set after flowering, some of the factors contributing to that outcome may have already occurred.

Nutrition cannot control the weather, but it can help ensure that the vine enters flowering without an avoidable nutritional limitation.

Nitrogen is not the only nutrient that matters

A good pre-flowering nutrition program should not be reduced to nitrogen.

Several nutrients are involved in the development of reproductive structures and the rapidly expanding canopy.

Boron

Boron deserves particular attention around flowering because it is involved in reproductive development, pollen function, cell-wall formation and sugar transport.

Boron deficiency can interfere with flowering and fruit set.

However, boron has a relatively narrow range between deficiency and toxicity. This makes routine tissue testing considerably safer than applying high rates simply because flowering is approaching.

Cold, wet conditions can also increase the risk of boron deficiency symptoms, which is relevant to spring conditions in Marlborough. (Yara New Zealand)

The objective is not to “push” boron.

It is to ensure that the vine is not deficient when reproductive demand increases.

Zinc

Zinc is involved in enzyme activity, growth regulation and reproductive development.

Like boron, zinc should be considered in the context of actual vineyard status rather than automatically applied to every block.

Soil type, pH, organic matter, rootstock and previous fertiliser history can all influence availability.

Potassium

Potassium becomes increasingly important as canopy growth accelerates and the vine’s demand for water and carbohydrate transport increases.

It is involved in stomatal regulation, osmotic control and the movement of assimilates throughout the plant.

However, potassium applications should also be based on vineyard testing.

Adding potassium to a vineyard that already has adequate levels is not necessarily beneficial and can potentially interfere with the balance of other cations.

Magnesium

Magnesium is central to chlorophyll and therefore photosynthetic capacity.

A rapidly expanding canopy has an increasing requirement for magnesium because new leaves are being produced at a high rate.

Maintaining adequate magnesium is particularly important if soil or tissue testing indicates low availability or if potassium applications have been historically high.

The pre-flowering canopy is the engine of the vineyard

This is where nutrition and canopy management become closely connected.

The objective during early spring is not simply to produce long shoots.

It is to produce a functional photosynthetic canopy capable of supporting the crop.

Marlborough research demonstrates why this matters.

A long-term Sauvignon Blanc study found that vines carrying different numbers of nodes developed different levels of vegetative growth before flowering. Vines with fewer retained nodes generally produced greater shoot length, shoot diameter and leaf number per shoot. (Wiley Online Library)

This illustrates an important principle:

the vine has a finite pool of resources.

Changing the number of shoots changes the distribution of those resources.

The same research showed that manipulating node number could influence yield and vine vigour, but the yield response changed over successive seasons as the vine compensated through changes in bunch size and bud development. (Wiley Online Library)

Nutrition therefore needs to be considered alongside pruning level, shoot number, irrigation and expected yield.

Don’t confuse vigour with nutritional sufficiency

One of the easiest mistakes in spring nutrition is assuming that a vigorous vineyard is necessarily well nourished.

It isn’t.

A vineyard can have:

• high shoot growth but inadequate reproductive nutrition;

• dark green foliage but excessive nitrogen;

• high soil nitrogen but poor nutrient balance;

• adequate soil nutrients but restricted root activity;

• adequate nutrients but insufficient water to transport them.

This is particularly important in Marlborough because vineyard soils and growing conditions vary considerably across the region.

Research has demonstrated substantial spatial variability in Marlborough vineyards, with differences in vine vigour being related to underlying site characteristics and subsequently associated with fruit composition and maturity. (DOI)

A blanket fertiliser program across an entire vineyard can therefore miss the actual requirement of individual blocks.

What should growers monitor?

The best pre-flowering nutrition program starts with measurement.

Rather than asking:

“What fertiliser should I apply before flowering?”

the better question is:

“What nutrient is limiting this block right now?”

Useful information includes:

1. Soil testing

Look at:

• pH

• organic matter

• mineral nitrogen

• phosphorus

• potassium

• calcium

• magnesium

• sulphur

• micronutrients

• cation balance where appropriate.

But soil analysis should not be interpreted in isolation.

2. Tissue analysis

Petiole or blade analysis can provide information about nutrient status during the growing season.

This is particularly useful where visual symptoms are absent.

The purpose is to identify developing deficiencies before they become obvious enough to affect canopy performance or reproduction.

3. Shoot growth

Measure shoot growth rather than relying solely on appearance.

Rapidly extending shoots, excessive internode length and a very dense canopy may indicate that nitrogen supply is exceeding the vine’s requirement.

Conversely, short shoots, small leaves and weak canopy development may indicate insufficient nitrogen, water limitation, poor root activity or another nutritional constraint.

4. Soil moisture

Nutrition cannot be separated from water management.

Nutrients must be dissolved in soil water and transported to the root system.

A vineyard can therefore have adequate nutrient concentrations in the soil but still exhibit poor nutrient uptake if the root zone is excessively dry, saturated or poorly aerated.

Marlborough’s cool climate makes timing particularly important

Marlborough Sauvignon Blanc has a relatively constrained growing season compared with warmer wine regions.

Local research has demonstrated that high crop loads can substantially slow ripening. In one long-term Marlborough trial, retaining 72 nodes compared with 24 nodes delayed target ripeness by as much as 41 days. (Wiley Online Library)

This creates an important nutritional consideration.

The goal of spring nutrition is not to maximise early vegetative growth at the expense of reproductive development and later crop balance.

The objective is to establish enough canopy to support the crop without creating excessive vigour or an unnecessarily large sink for carbohydrates and nutrients.

That balance becomes increasingly important as yield increases.

What about nitrogen timing?

Nitrogen should be considered as a seasonal program rather than a single application.

Where nitrogen is genuinely required, supplying some available nitrogen during active spring growth can help support canopy establishment.

However, the rate and timing should be adjusted to:

• soil nitrogen supply

• vine vigour

• expected crop load

• irrigation

• variety and rootstock

• historical tissue results

• organic matter

• block yield history.

Importantly, local research does not support the simplistic idea that all nitrogen needs to be applied before flowering.

Research and industry observations from Marlborough indicate that nitrogen supplied later in the season can contribute to vine reserves and may influence fruit and wine composition. (Rural News Group)

The better approach is therefore to match nitrogen supply to the vine’s changing demand.

The flowering window should be treated as a checkpoint

Flowering is an excellent time to stop and assess the vineyard.

Ask:

Is the canopy developing at the desired rate?

Are shoots becoming excessively vigorous?

Are leaves showing signs of nutrient limitation?

Is soil moisture adequate?

Does tissue analysis indicate a developing deficiency?

Is the crop load appropriate for the available canopy?

Are there signs that the vines are entering flowering under nutritional stress?

This is much more useful than applying a standard “pre-flowering fertiliser” simply because the calendar says it is time.

The key message for Marlborough growers

Pre-flowering nutrition is important because it coincides with one of the most resource-demanding periods in the grapevine’s annual cycle.

The vine is moving from dependence on stored reserves towards current photosynthesis, rapidly expanding its canopy and developing its reproductive structures.

Marlborough research makes the importance of this period particularly clear.

Long-term Sauvignon Blanc trials in the region show that many of the environmental conditions associated with yield occur before flowering, while carbohydrate and nitrogen reserves are highly dynamic around flowering. (IVES)

That means the nutritional status of the vine entering flowering matters.

But the answer is not simply to apply more fertiliser.

The objective should be to remove nutritional limitations while maintaining balance.

For Marlborough Sauvignon Blanc, the ideal pre-flowering vine is not the one with the biggest shoots or darkest green leaves.

It is the vine with:

adequate nitrogen, balanced mineral nutrition, sufficient water, a functional canopy and enough nutritional and carbohydrate capacity to carry the crop through flowering and fruit set.

By the time poor fruit set or weak canopy development becomes obvious, some of the opportunity to correct the problem may already have passed.

Pre-flowering nutrition is therefore not just about feeding the vine.

It is about preparing the vine for the crop it is about to carry.

Research from Marlborough and New Zealand

• Zhu, J., Fraysse, R., Trought, M.C.T., Raw, V., Yang, L., Greven, M. & Agnew, R. (2020). Quantifying the seasonal variations in grapevine yield components based on pre- and post-flowering weather conditions. OENO One 54(2). The study used long-term Sauvignon Blanc data from four Marlborough vineyards and identified critical pre-flowering periods for several yield components. (Oeno One)

• Greven, M.M., et al. (2014). Influence of retained node number on Sauvignon Blanc grapevine vegetative growth and yield. Australian Journal of Grape and Wine Research. The multi-year field experiment was conducted at the Marlborough Research Centre and examined 24–72 nodes per vine. (Wiley Online Library)

• Greven, M.M., et al. (2015). Influence of retained node number on Sauvignon Blanc grapevine phenology in a cool climate. Australian Journal of Grape and Wine Research. The research examined crop load, phenology and ripening in Marlborough Sauvignon Blanc. (Wiley Online Library)

• Eltom, M., Trought, M.C.T., Agnew, R., Parker, A. & Winefield, C.S. (2017). Pre-budburst temperature influences the inner and outer arm morphology, phenology, flower number, fruitset, TSS accumulation and variability of Vitis vinifera L. Sauvignon Blanc bunches. Australian Journal of Grape and Wine Research. The field experiment was conducted on commercial Sauvignon Blanc vines in Marlborough. (Wiley Online Library)

• Trought, M.C.T., et al. (2011). Vineyard variability in Marlborough, New Zealand: characterising spatial and temporal changes in fruit composition and juice quality in the vineyard. Australian Journal of Grape and Wine Research. (DOI)

• Bramley, R.G.V., et al. (2023) and associated Marlborough research discussed in Winegrower: research examining relationships between soil fertility, yield, vine nitrogen and Sauvignon Blanc composition in Marlborough. (Rural News Group)