🌱 Plants Calculators

Plan plant spacing, seed quantities, planting depths, garden layouts, and find your USDA growing zone.

All Plants Tools

Plant Spacing Calculator Calculate how many plants fit in a garden bed based on area size and recommended plant spacing. Seed Calculator Calculate how many seeds you need based on garden area, plant spacing, and germination rate. Planting Depth Guide Find the correct planting depth for common vegetable seeds based on seed size and type. Garden Layout Planner Plan how many rows and columns of plants fit in your garden space with recommended spacing. Growing Zone Finder Find your USDA Plant Hardiness Zone based on your average annual minimum winter temperature.

Plant Spacing: Why It Matters

Correct plant spacing is one of the most important decisions in garden planning, yet it is frequently underestimated by beginners. Plants spaced too closely compete for light, water, and soil nutrients, leading to stunted growth, poor yields, and increased disease pressure from reduced air circulation. Plants spaced too far apart waste growing space and allow weeds to establish in bare soil. Most vegetable spacing recommendations are based on the mature canopy size — the point at which adjacent plants just touch, shading out weeds while not overcrowding each other. Square-foot gardening intensifies these recommendations by using a 30 cm (12 inch) grid and growing one large plant, four medium plants, nine small plants, or sixteen mini plants per square foot.

Seed Germination and Quantity Planning

When planning seed quantities, germination rate is the critical variable. A packet labelled "germination rate 85%" means that on average 85 out of 100 seeds will sprout under ideal conditions. To achieve 100 established plants with an 85% germination rate, you need to sow at least 118 seeds (100 ÷ 0.85). In practice, gardeners also account for losses to pests, frost, and transplant shock — for important crops, sowing 150–200% of the target plant count is wise. Germination rates decline over time: most vegetable seeds remain viable for 2–4 years if stored cool and dry, while onion and parsnip seed should be used fresh each season (viability drops sharply after one year).

Planting Depth Guidelines

The general rule for planting depth is 2–3 times the diameter of the seed, but this varies by species. Fine seeds like carrots and lettuce (under 1 mm) should barely be covered — press them onto moist soil surface or cover with just 3–5 mm of compost. Medium seeds like peas and beans are planted 3–5 cm deep; the deeper placement helps them anchor against disturbance and access moisture below the surface. Large seeds like squash, courgette, and sweetcorn are planted 2–4 cm deep. Planting too deep prevents germination — seeds have finite energy reserves and cannot reach the surface if buried too far. Planting too shallow exposes seeds to drying out and disturbance.

USDA Growing Zones and Planting Timing

The USDA Plant Hardiness Zone Map divides North America into 13 zones based on the average annual extreme minimum temperature, ranging from Zone 1 (below −51°C) to Zone 13 (above 18°C). Each zone is divided into an "a" (colder) and "b" (warmer) half, representing 2.8°C (5°F) increments. The zone tells you which perennial plants will survive your winters — a plant rated "hardy to Zone 6" will reliably overwinter in Zone 6 and warmer but may die in Zone 5. For annual vegetables, the zone determines your frost dates, which govern when to start seeds indoors, when to transplant outdoors, and when the first autumn frost will end the growing season. The UK uses a similar system with RHS hardiness ratings H1–H7.