Price as of Jul 24, 2026. Product prices and availability are accurate as of the date indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.

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Example Calculations

1Standard 6 ft Spiral (3 ft tall, 6" stones)

Inputs

Diameter6 ft

Height3 ft

Stone Height6 inches

Result

Plant Slots63

Stones~300

Soil5.7 ft³

Planting Area32 ft²

Slant height = sqrt(9+9) = 4.24. Area = pi × 3 × 4.24 = 40 ft². Plant slots at 6" spacing = 40/0.5 ≈ 80 (varies by calculation).

2Small 4 ft Spiral (2 ft tall, 4" stones)

Inputs

Diameter4 ft

Height2 ft

Stone Height4 inches

Result

Plant Slots~28

Stones~120

Soil2.5 ft³

Planting Area14 ft²

Slant height = sqrt(4+4) = 2.83. Area = pi × 2 × 2.83 = 17.8 ft². Soil = 0.6 × 1/3 × pi × 4 × 2 = 5.0 × 0.6 = 3.0 ft³.

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Frequently Asked Questions

How big should an herb spiral be?

A standard herb spiral is 5–6 ft in diameter and 3 ft tall at the center. This size fits 20–30 herbs in microclimates from hot/dry at the top to cool/moist at the base. A 4 ft diameter works for small spaces but holds only 10–15 plants.

Small (4 ft diameter): 10–15 herbs, good for patios and small gardens
Standard (5–6 ft): 20–30 herbs, ideal for most home gardens
Large (7–8 ft): 30–50 herbs, provides more growing space and microclimates
Height: 2–4 ft at center, tapers to ground at outer edge
Footprint: a 6 ft spiral takes just 28 sq ft of ground space

How many stones do I need for an herb spiral?

A 6 ft diameter, 3 ft tall herb spiral with 6-inch stones needs approximately 200–400 stones depending on stone size and wall thickness. Flat fieldstone or broken concrete work well. Budget about 1 ton of stone for a standard 6 ft spiral.

6 ft spiral: approximately 200–400 stones, about 1 ton total weight
Use flat stones (4–8" tall) for stable, easy stacking
Fieldstone, flagstone, or broken concrete are common choices
No mortar needed — dry-stack allows drainage and easy adjustments
Reclaimed brick or urbanite (broken concrete) works great and is free

What herbs go where on an herb spiral?

Top (hot/dry): Mediterranean herbs like rosemary, thyme, oregano, and lavender. Middle: sage, cilantro, parsley, and chives. Bottom (cool/moist): mint, lemon balm, and chamomile. The spiral creates microclimates matching each herb's native conditions.

Top (hot, dry, full sun): rosemary, thyme, oregano, lavender, marjoram
Upper middle (warm, well-drained): sage, tarragon, savory, hyssop
Lower middle (moderate moisture): parsley, cilantro, chives, dill
Bottom (cool, moist, partial shade): mint, lemon balm, chamomile, sorrel
North-facing side gets shade — plant shade-tolerant herbs there

How much soil does an herb spiral need?

A 6 ft diameter, 3 ft tall herb spiral needs about 10–15 cu ft of soil mix (roughly 5–7 bags of potting soil). Use a 50/50 mix of compost and garden soil. Add gravel at the base for drainage, especially in clay soil areas.

6 ft spiral: 10–15 cu ft of soil mix (about 0.4–0.6 cubic yards)
Soil mix: 50% compost + 50% garden soil for most herbs
Add sand or perlite for Mediterranean herbs at the top (better drainage)
Richer compost at the bottom for moisture-loving herbs
Base layer: 3–4 inches of gravel or rubble for drainage foundation

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Last Updated: Jul 24, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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Herb Spiral Calculator — Stone, Soil & Plants by Diameter

Calculate materials for a spiral herb garden with multiple microclimates

Plant Slots

160

Stones

168

Soil

17 ft³

Area

40 ft²

Diameter (ft)

Typical: 4–8 ft

Height (ft)

Typical: 2–4 ft

Stone Height (inches)

Plant Slots

160

6 ft diameter spiral

Stones

168

Soil

ft³

Area

ft²