Choosing Probe Size

• Buying Guides
• How Many Probes to Install
• Where to Position Probes

• 30 cm -> Shallow-rooted crops: target the 0-30 cm layer (leafy vegetables, young plants)
• 60 cm -> Intermediate-rooted crops: target 30-60 cm (vegetables, potato, tomato, etc.)
• 90 cm -> Deep-rooted crops: also monitor 60-90 cm depending on soil profile (vineyard, orchards, field crops)
• 120 cm -> Deep soils / trees / strongly rooted crops: target 120 cm
  
  Probe size selection depends mainly on crop type and its root zone, as well as the depth where moisture should be measured. It is important to account for rooting depth so the probe is installed at the right level.

The tables below summarize typical root depths for different crops. A more complete filterable table is available further down.

🌾 Field crops

🥦 Vegetables and market gardening

🍇 Vine and perennial crops

🍎 Tree crops / orchards

🌱 Small crops / young plantations / greenhouse

Search average root depths by crop type and variety, along with the effect of moisture on this depth. This table is not exhaustive but gathers nearly 200 different crops.

Root depth references by crop

Search a crop or categoryAllAlliumBulb cropBulb vegetableCerealFiber cropFlower vegetableForage grassForage legumeFruit treeIndustrial cropIndustrial root cropLeaf vegetableLegumeMarket gardeningMediterranean tree cropOilseedPerennialPerennial cropProtein cropPseudocerealRoot cropSmall fruitTropical cropTropical market gardeningTropical tree cropTropical tuberTuberTuberous rootVegetable legumeViticultureFilter

Crop	Sub-crop / type	Average maximum rooting depth	Moisture influence
Soft wheat	Cereal	1.2 to 1.8 m	Moderate moisture supports root exploration; drought pushes roots deeper if soil remains permeable (3)(5).
Durum wheat	Cereal	1.0 to 1.6 m	Similar to soft wheat, with rooting limited by compaction and lack of surface water (3)(5).
Barley	Cereal	0.9 to 1.5 m	Shallower roots in moist soil, deeper roots under mild water stress (5).
Oat	Cereal	0.8 to 1.2 m	Regular moisture keeps most roots in the top horizon (4)(5).
Rye	Cereal	1.5 to 2.0 m	Good drought tolerance, with deeper rooting favored in dry conditions (3)(5).
Triticale	Cereal	1.2 to 1.8 m	Greater depth when deeper horizons remain accessible to water (3)(5).
Rice	Cereal	0.3 to 0.8 m	Saturated and hydromorphic soils limit downward root growth (3).
Maize	Cereal	1.5 to 2.5 m	Under moderate water deficit, roots elongate toward wetter layers; under severe stress, extension slows (5).
Sorghum	Cereal	1.5 to 3.0 m	Very effective at exploring deep reserves, especially when the surface dries (3)(5).
Pearl millet	Cereal	1.0 to 2.0 m	Depth increases under low rainfall but decreases in compacted soil (5).
Fonio	Cereal	0.4 to 0.8 m	Rather shallow rooting, highly dependent on moisture in the cultivated horizon (3).
Quinoa	Pseudocereal	1.0 to 2.0 m	Good root plasticity in dry conditions; deeper rooting in open soil profiles (5).
Buckwheat	Pseudocereal	0.6 to 1.0 m	Prefers well-structured, not overly dry horizons; often remains shallower (3).
Amaranth	Pseudocereal	1.0 to 2.0 m	Can root deeper when surface moisture decreases (5).
Sunflower	Oilseed	1.5 to 3.0 m	Taproot is very sensitive to moisture gradients and goes deeper when surface water is limited (5).
Rapeseed	Oilseed	1.0 to 1.5 m	Regular moisture limits depth; drought encourages deeper exploration (3)(5).
Turnip rape	Oilseed	1.0 to 1.5 m	Depth varies with moisture persistence in the plow layer (5).
Soybean	Protein crop	1.0 to 1.8 m	Deeper roots under moderate water deficit (2)(5).
Field pea	Legume	0.8 to 1.5 m	Sensitive to excess water; cool but aerated soils support better downward growth (1)(5).
Faba bean	Legume	1.0 to 2.0 m	Moisture supports growth, but accessible deep horizons help plants seek water in summer (3)(5).
Lentil	Legume	0.7 to 1.2 m	Can remain shallow if surface moisture is sufficient (5).
Chickpea	Legume	1.0 to 2.0 m	Strong drought response with root extension toward deeper layers (5).
Dry bean	Legume	0.6 to 1.2 m	Excess water limits root aeration; moderate moisture is ideal (1)(5).
White lupin	Legume	1.5 to 2.5 m	Tolerates poor, dry soils fairly well, with deep rooting (5).
Yellow lupin	Legume	1.0 to 2.0 m	Greater depth under water stress, but sensitive to soil asphyxia (5).
Alfalfa	Forage legume	2.0 to 5.0 m	Very deep rooting in deep, non-compacted soils; surface moisture is less critical after establishment page:page1.
Red clover	Forage legume	0.8 to 1.5 m	Prefers regular moisture; roots less deeply in dry, dense profiles (5).
White clover	Forage legume	0.3 to 0.8 m	Strongly dependent on surface moisture, with shallow rooting (5).
Sainfoin	Forage legume	1.0 to 2.0 m	Can exploit deep water reserves better than clovers (5).
Vetch	Forage legume	0.8 to 1.5 m	Moisture strongly affects root elongation rate (5).
Perennial ryegrass	Forage grass	0.5 to 1.0 m	Roots are mostly concentrated in moist surface layers (4)(5).
Orchard grass	Forage grass	1.0 to 2.0 m	Responds well to drought thanks to deeper rooting (5).
Tall fescue	Forage grass	1.0 to 2.0 m	Greater depth when the surface dries (2)(5).
Red fescue	Forage grass	0.6 to 1.2 m	More shallow, dependent on moisture in the top horizon (5).
Kentucky bluegrass	Forage grass	0.3 to 0.8 m	Very sensitive to surface drying, with limited rooting depth (5).
Sugarcane	Industrial crop	1.5 to 3.0 m	Deep water availability supports growth during dry periods (5).
Sugar beet	Industrial root crop	1.0 to 2.0 m	Soil density and moisture strongly control root depth and root shape (1)(5).
Fodder beet	Industrial root crop	1.0 to 2.0 m	In moist but aerated soils, roots penetrate better; excess water reduces rooting (1).
Potato	Tuber	0.4 to 0.8 m	Overly wet soil = asphyxia risk; moderately moist soil = correct rooting (1)(5).
Sweet potato	Tuber	0.5 to 1.0 m	Roots explore better in loose, warm soil with regular moisture (5).
Cassava	Tuberous root	1.0 to 2.0 m	Strong performance under water stress thanks to a deep root system (5).
Yam	Tuber	0.6 to 1.5 m	Requires loosened, sufficiently moist soil for root elongation (5).
Peanut	Oilseed	1.0 to 1.8 m	Regular moisture supports flowering, but roots can seek water in deeper layers (5).
Sesame	Oilseed	1.0 to 2.0 m	Good adaptation to dry conditions; roots deepen when surface water declines (5).
Cotton	Fiber crop	1.0 to 2.5 m	Taproot is favored in dry, deep profiles (5).
Flax	Fiber crop	0.8 to 1.5 m	Prefers moderate moisture; excess water can cause root asphyxia (5).
Hemp	Fiber crop	1.0 to 2.0 m	Rooting increases in well-structured, non-saturated soils (5).
Tobacco	Industrial crop	1.0 to 2.0 m	Needs balanced moisture and aeration; too much water reduces deep exploration (1).
Tomato	Market gardening	0.8 to 1.5 m	With regular moisture, roots stay mostly shallow; under deficit, they explore deeper page:page1.
Grafted tomato	Market gardening	1.0 to 2.0 m	Rootstock may improve access to deep water page:page1.
Chili pepper	Market gardening	0.6 to 1.2 m	In overly wet soil, roots stay shallower; under light stress, elongation increases page:page1.
Bell pepper	Market gardening	0.6 to 1.2 m	Very sensitive to soil aeration; excessive moisture limits development page:page1.
Eggplant	Market gardening	0.8 to 1.5 m	Performs well in moist but drained profiles; deep water becomes useful in summer page:page1.
Cucumber	Market gardening	0.4 to 0.8 m	Rather shallow system, highly dependent on moisture in the seedbed page:page1.
Zucchini	Market gardening	0.5 to 1.0 m	Regular moisture supports uptake; excess water slows root respiration (1)(5).
Squash	Market gardening	0.8 to 1.5 m	In dry conditions, roots may go deeper to sustain the plant (5).
Melon	Market gardening	0.8 to 1.5 m	CTIFL work specifically tracks root structure under seasonal conditions [page:page1].
Watermelon	Market gardening	1.0 to 1.8 m	Good exploration of deep layers when the surface dries (5).
Lettuce	Market gardening	0.2 to 0.4 m	Very shallow, dependent on regular surface moisture (5).
Leaf lettuce	Market gardening	0.2 to 0.4 m	Excess water can asphyxiate roots; drought quickly reduces growth (5).
Chicory	Market gardening	0.6 to 1.2 m	Loose, cool horizons are favorable; depth increases under moderate stress (5).
Endive	Market gardening	0.4 to 0.8 m	Moderate rooting, dependent on moisture in the arable horizon (5).
Carrot	Root crop	0.6 to 1.2 m	Loose, moist soil: longer roots; compacted soil: reduced depth (1).
Radish	Root crop	0.2 to 0.6 m	Fast growth, but sensitive to water deficit and soil obstacles (4)(5).
Black radish	Root crop	0.4 to 0.8 m	Can root deeper than surface radish if moisture stays stable (4).
Beetroot	Root crop	0.6 to 1.0 m	Regular moisture = better growth; excess water = reduced aeration (1).
Turnip	Root crop	0.4 to 0.8 m	Growth slows if soil dries too early (5).
Parsnip	Root crop	0.8 to 1.2 m	Needs a deep, moist profile initially, then better drainage (5).
Celeriac	Root crop	0.4 to 0.8 m	Highly dependent on moisture and sensitive to water stress breaks (5).
Onion	Bulb crop	0.3 to 0.6 m	Shallow roots, needs regular moisture without saturation (5).
Garlic	Bulb crop	0.3 to 0.6 m	Excess water promotes diseases and limits rooting (1).
Shallot	Bulb crop	0.2 to 0.5 m	Very shallow, stable moisture is essential (5).
Leek	Allium	0.4 to 0.8 m	Performs better in cool profiles than in waterlogged conditions (5).
Asparagus	Perennial	1.0 to 2.0 m	Fleshy roots explore deeper layers better in well-drained soil (5).
Strawberry	Small fruit	0.2 to 0.4 m	Shallow roots, very sensitive to drying (5).
Raspberry	Small fruit	0.4 to 0.8 m	Requires regular moisture; roots remain shallow (5).
Blackcurrant	Small fruit	0.3 to 0.8 m	Prefers cool but drained soil without saturation (5).
Gooseberry	Small fruit	0.3 to 0.8 m	Mostly shallow roots, sensitive to water stress (5).
Blueberry	Small fruit	0.3 to 0.6 m	Highly dependent on moisture and soil acidity (5).
Grapevine	Viticulture	1.0 to 3.0 m	Moderate drought pushes roots deeper; frequent irrigation keeps them shallower (3)(5).
Apple tree	Fruit tree	1.0 to 2.5 m	Deep, non-asphyxiating soil supports broader root architecture (1)(5).
Peach tree	Fruit tree	0.8 to 1.8 m	Sensitive to excess water; moderate moisture is preferable (5).
Apricot tree	Fruit tree	1.0 to 2.0 m	Roots develop better in drained soils with deep water availability (5).
Pear tree	Fruit tree	1.0 to 2.5 m	Greater depth when deep horizons remain accessible to water (5).
Cherry tree	Fruit tree	1.0 to 2.0 m	Does not tolerate excess water; needs good drainage (5).
Plum tree	Fruit tree	0.8 to 1.8 m	Regular moisture supports exploration, but saturation reduces it (5).
Walnut tree	Fruit tree	2.0 to 4.0 m	Very large root system when soil is deep and well structured (3).
Olive tree	Mediterranean tree crop	1.5 to 4.0 m	Very good use of deep water under dry climates (5).
Almond tree	Mediterranean tree crop	1.5 to 3.0 m	Deep roots favored by dry periods (5).
Nectarine tree	Fruit tree	0.8 to 1.8 m	Rooting is sensitive to aeration and excessive moisture (5).
Kiwi	Fruit tree	0.6 to 1.5 m	Prefers cool, well-drained soil; too much water limits roots (5).
Citrus	Fruit tree	0.8 to 1.8 m	Highly sensitive to root asphyxia if soil remains too wet for too long (5).
Avocado tree	Tropical tree crop	1.0 to 2.5 m	Needs moisture, but excess water strongly reduces root oxygenation (5).
Mango	Tropical tree crop	1.5 to 4.0 m	Drier deep layers often stimulate root exploration (5).
Banana	Tropical crop	0.5 to 1.2 m	Very dependent on constant surface moisture, with shallow rooting (5).
Papaya	Tropical crop	0.5 to 1.0 m	Roots are sensitive both to drought and to waterlogging (5).
Pineapple	Tropical crop	0.2 to 0.5 m	Very shallow roots, quickly reactive to moisture changes (5).
Coffee	Perennial crop	1.0 to 2.0 m	Regular moisture is favorable, but deeper dry layers may be explored in deep soils (5).
Cocoa	Perennial crop	1.0 to 2.0 m	Prefers moisture, but good drainage is essential (5).
Rubber tree	Perennial crop	2.0 to 4.0 m	Deep roots if the profile is not saturated (5).
Oil palm	Perennial crop	1.5 to 3.0 m	Strong response to water availability, with an extensive root system in deep soils (5).
Pepper (black pepper)	Perennial crop	0.4 to 1.0 m	Highly dependent on moisture in the top profile (5).
Tea	Perennial crop	1.0 to 2.0 m	Prefers regular moisture without waterlogging (5).
Cabbage	Leaf vegetable	0.4 to 0.8 m	Stable surface moisture is needed, with moderate rooting (5).
Broccoli	Flower vegetable	0.4 to 0.8 m	Very dry soils reduce growth, and waterlogged soils do as well (5).
Cauliflower	Flower vegetable	0.4 to 0.8 m	Highly sensitive to moisture fluctuations (5).
Spinach	Leaf vegetable	0.3 to 0.6 m	Prefers cool soil; rooting remains limited (5).
Swiss chard	Leaf vegetable	0.4 to 0.8 m	Tolerates moisture fluctuations slightly better (5).
Romaine lettuce	Leaf vegetable	0.2 to 0.5 m	Shallow roots; quick water stress when the surface dries (5).
Fennel	Bulb vegetable	0.5 to 1.0 m	Deeper rooting if soil is loose and moist at establishment (5).
Rutabaga	Root crop	0.5 to 1.0 m	Regular moisture = better development, excess moisture = root limitation (5).
Jerusalem artichoke	Tuber	1.0 to 2.0 m	Can root quite deeply if the profile remains open (5).
Taro	Tropical tuber	0.5 to 1.0 m	Likes moisture but is vulnerable to prolonged root asphyxia (5).
Okra	Tropical market gardening	1.0 to 1.8 m	Roots more deeply when the surface dries (5).
African yam bean	Tuber	0.6 to 1.5 m	Highly dependent on soil structure and moisture (5).
Snow pea	Vegetable legume	0.5 to 1.0 m	Moderate rooting, sensitive to strong moisture variation (5).
Green bean	Vegetable legume	0.4 to 0.8 m	Prefers light but regular irrigation (5).
Garden pea	Vegetable legume	0.5 to 1.0 m	Surface moisture strongly controls root development (5).

1: Soil profile - Agri-Réseau (article / PDF). https://www.agrireseau.net/documents/Document_101213.pdf
2: Fan et al. - Root distribution by depth for temperate agricultural crops (scientific paper, PDF). https://www.verdeterreprod.fr/wp-content/uploads/2020/05/fan-et-al-2016-beta-root-depth.pdf
3: The importance of deep soil horizons - Planet-Vie (ENS), science outreach article. https://planet-vie.ens.fr/thematiques/ecologie/l-importance-des-horizons-profonds-des-sols
4: Two-year trial synthesis on soil structure - Cultivons les couverts (Agro-Transfert), technical article. https://cultivons-les-couverts.agro-transfert-rt.org/synthese-structure/
5: Responses of root system architecture to water stress at multiple levels (open-access scientific review). https://pmc.ncbi.nlm.nih.gov/articles/PMC9780461/