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Place · November 2, 2025 · 9 min read

Terroir: Soil, Site & Climate

By Matthew C. Perez

TL;DR (for the skimmers)

Balanced limestone-leaning soils (high Ca, moderated Mg, controlled K) with mid CEC and smart topography (east aspect, drainage paths) yield tension, precision, and resilience, tends to be ideal for sparkling bases and refined still wines.

Definition of place

Terroir is a seemingly French term that is the sum of place: geology, soil chemistry and structure, biology, water, slope, aspect, wind, and macro, meso, microclimate interacting with a variety and a grower's choice(s). There are multiple influences related to terroir and its effects on the end result in the bottle. If you learn to read a soil report and pair it with topography, you can anticipate style, tannin/texture, acid retention, and disease pressure before planting a single vine.

This post starts a journey into aspects of soil put into plain English, then in future posts we zoom out to site selection and topographic design decisions that mitigate climate risk. Maybe at the end I will make a post about some recent soil samples at a probable vineyard site I plan to plant, and we can evaluate it together, maybe.

Evaluation of soil and its effects on wine.

Organic Matter (OM)

  • Why it matters: Drives microbial life, nutrient cycling, water-holding, and crumb structure. Too low and that means there is not enough activity below the surface leading to weak biology; too high usually means you have heavy soils which often translates toward too much vigor and shading of the fruit.
  • Style impact: Healthy OM supports even ripening and fine-grained tannins; in sparkling, it lowers stress and preserves delicacy. Higher vigor can lead to higher yields, but these higher yields often lack the focus and profile of a higher-end wine.

pH (soil)

  • Why it matters: Sets the chemical "operating system" for vines. Different pH levels determine the availability of minerals and nutrients available to the vine. For example, in calcareous sites, slightly alkaline pH can limit Zinc and Iron and to some extent Manganese and Boron availability which can cause chlorosis. This can be moderated with foliar sprays in season or amending the soil in the dormant season, however some levels of pH can lock out uptake from soil, making foliar sprays situationally more desirable/effective.
  • Style impact: Neutral-to-alkaline Ca+ soils correlate with tension and linearity, especially for base wines. Higher soil pH tends to promote vines to preserve organic acids like malic and tartaric when ripening. This tends to give a "juicy" mouthfeel, the wine hits (punches) the palate and causes the salivary glands to react. Some of the flagship examples of this include Champagne and Burgundy. Climate and location do have some role to play in these styles.
  • Desirable Range: In general, some acidity is okay, just like some alkalinity is okay. Each direction brings different aspects, wine flavors, and growing challenges. Another factor is your base soils. For base limestone/calcareous soil your pH may be between a desirable range of 7.2–8.2 (with 7.0 up to 8.5 being workable), but as you scale more challenges will impact your ability to farm vines, like nutrient (Mg, Bn, etc) lockout. For non-calcareous soils, desirable range is 6.2–6.8 (with 6.0–7.0 being acceptable).

Cation Exchange Capacity (CEC)

  • Why it matters: A proxy for clay/organic colloids (the thing that nutrients "bond" to) and nutrient-holding "battery." CEC is the soil's ability to attract, hold, and supply nutrients to vines. With good CEC the typical nutrients that we care most about for a vineyard will be available for vines in most all climatic conditions, won't wash away in heavy water events or lock up in drought. Petrus makes some of the highest priced red wine in the world from Right Bank Clay and we have multiple vineyards in the sandy Barossa Valley that are pre-civil war vines on their own (vinifera) rootstock. In general, we want the nutrients available, but maybe not too available.
  • Style impact: Midrange CEC (15–25) balances supply and precision. Too low, water events can really stress vines; too high, too many nutrients available and uptake can be sluggish, vigor-prone vines. Vigor tends to create thinner wine with less minerality and presence of place to shine through. Lower CEC can sometimes lead to vine stress which most of us agree tends to be one component of quality wine.
  • Ideal Range: Between 10–20 meq/100g is generally ideal, but this is not as nuanced as some of the measurements. For example, sandy soils will be below 10, silty and loamy in 10–18 range and clay based greater than 18.

CEC Percent Base Saturation (Computed)

  • Why it matters: This is the share of the soils that are represented by each of the minerals, what minerals are available to the vine in the soil. The rest of the elements are acidic ions like Hydrogen and in some soil types, Aluminum. These acidic ions/elements take away from the availability of "good" soil nutrients like Ca, Mg, etc.
  • Best situation for CEC Percent Base Saturation: Ideally, these measurements lead to precision and noticeable acidity, with a tight structure. But the main takeaway is these nutrients and their ratios between each lead to tastable outcomes.

Ratios > absolute numbers (why base saturation matters)

Base saturation shows the proportion of exchange sites occupied by Ca, Mg, K (and Na). Ratios are powerful because they predict structure and sap pH dynamics, two things you actually taste.

  • High Ca% (85–95) means airy structure, deep roots, fast drainage after rain. As this percentage goes down wine becomes less linear and more round in the mouth.
  • Moderate Mg% (4–8) avoids soil compaction, supports steady photosynthesis. Too much and we can get rounder mouthfeel too. Mg can become "locked out" if Ca gets up over high, stressing Mg uptake.
  • Managed K% (2–5) → keeps berry pH in check; keeping K this low is essential for sparkling. As K continues to rise above 5, pH can creep. K generally becomes more available at veraison and the next 3 weeks after.

Calcium (Ca) Magnesium (Mg) & the Ca:Mg ratio

  • Why it matters: Ca flocculates clays resulting in good tilth, drainage, and deep rooting. Mg compacts the soil when dominant.
  • Rule of thumb: Ca:Mg ratio between ~20–40:1 yields open structure and vertical rooting great for texture and "chalk grip." Keeps root paths open.
  • Some Examples of Ca:Mg ratios: Champagne 8–16:1, Côte d'Or 4–8:1, Barolo 5–10:1, Napa 3–10:1, Mosel 3–7:1

Potassium (K) Magnesium (Mg) & the K:Mg ratio

  • Why it matters: K accumulates in berries and raises juice pH; high K can flatten sparkling bases and still wine. SO₂ becomes less effective in some cases resulting in Brettanomyces flavors and scents.
  • Key ratio: K:Mg ~1–2:1 for linear acid retention; 2–3+ trends toward softer reds.
  • Example K:Mg ratios: Champagne 2–5:1, Côte d'Or 2.5–7:1, Barolo 2–6:1, Napa 1–4:1, Mosel 1–3:1

Calcium (Ca) Potassium (K) & the Ca:K ratio

  • Why it matters: A higher Ca:K ratio helps keep juice/must pH low, which translates to more linear, ageable wine that tends to be tighter when first released for sale. This ratio can support the evolution of wine in the bottle and sometimes soften it over time. If this ratio drops, pH of juice/must rises alongside of it.
  • Key ratio: Ca:K ratio: Ideal ratio of Ca:K 20–40:1. Keep an eye on the ratio if Ca:K tests at or starts to leach over time at 15:1, K uptake rises in grapes. On the other end if Ca:K is in the 60:1 range on very low-K soils can tip into K deficiency which can mean weak canopies, marginal chlorosis, and/or poor sugar transport. Use soil tests and mid-season tissue tests to confirm before adding K.
  • Example Ca:K ratios: Champagne 30–60:1, Côte d'Or 16–35:1, Barolo 15–40:1, Napa 10–40:1, Mosel 8–25:1

Putting it all together

Nutrient antagonism & vine health

As K rises it tends to suppress Mg uptake. Where very high Ca can also compete with Mg. Poor Magnesium. These are classic antagonisms in grapes, Mg deficiency, lower photosynthesis, and yield/quality penalties. In general, let's work to keep Mg:K above 1:1 where possible in calcareous sites and 2:1 being ideal.

Wine pH & style

High grape K trends to higher must/wine pH, reducing freshness, color (reds), and microbial stability. That's why Champagne, Chablis, and style programs chase low K uptake and higher Ca:K and Mg:K ratios that support that linear palate attack. It is not as important in still reds, but we still want to keep a handle and not allow wine to become too round, which could be leveraged if we are trying to produce an immediate drinker that does not need to age and maybe in a blending program to add mouthfeel.

Soil structure, infiltration, and rooting

Ca:Mg affects clay flocculation (open soil) and aggregate stability. Too much Mg relative to Ca, dispersion, crusting, poorer infiltration (less open soils). We love adequate Ca dominance to keep pores open which is why limestone terroir is prized, Ca:Mg ratio is critical on marls/clays and in rain events to swiftly move water through the below-ground structure.

Micronutrients on calcareous ground

High CaCO₃/bicarbonate elevates pH and depresses Fe/Mn/Zn solubility. Active CaCO₃ is Ca that is "alive" and interacts with the exchange of nutrients. For example, if active Ca dominates this exchange, it tends to limit K and hold juice pH below our high acidity benchmarks for crisp whites and sparkling wine. However, with this type of terroir-specific opportunity Mg stress shows sooner, even when ratios look "OK." We can support and supplement vines experiencing Mg stress, foliar Mg and chelated micros to offset Mg lockout or uptake.

FAQ

Q1: What is CEC and why does it matter? CEC (cation exchange capacity) measures how many nutrient "parking spots" soil has. You want parking spots, not too little of them to where people cannot get in and out of your strip mall. Also, not too many where it looks empty and vacant where undesirables start to move in and inhabit. We want that mid-range (≈15–25) which keeps supply steady without excess vigor, supporting precise flavors and even ripening.

Q2: What does the Ca:Mg ratio tell me? It predicts soil structure. Ca around 20–40× Mg keeps clays flocculated, improving drainage and root depth. Wines show chalky grip and linear acidity rather than broad, soft textures.

Q3: Why control potassium (K) in sparkling programs? K accumulates in berries and raises juice pH. Keeping K:Mg ~1–2:1 preserves acid line and freshness that is critical for crisp whites and méthode traditionnelle sparkling bases.

Q4: How does topography mitigate climate risk? East aspects soften afternoon heat; 5–12% slopes shed water and cold air downhill. Preserve a low swale or unplanted corridor to let frost drain off the block. Even better if you have a moderating influence at the base of the slope like a lake or even a moving river to carry the cold air away.

Q5: Do absolute nutrient ppm matter less than ratios? Both matter, but base-saturation ratios (Ca:Mg:K) better predict structure, sap pH, and flavor precision than raw ppm alone. How much you have is important but how they interact provides answers to the data. It's not the size of the... boat, it's the...