Why These Three Numbers Matter More Than Anything Else
Every seed packet lists planting depth, spacing, and a sowing window — and yet these three numbers are the most commonly skipped or eyeballed details in the garden. Plant a tomato too shallow and its roots never establish firm footing. Crowd your lettuce rows and airflow drops, inviting fungal disease. Sow squash three weeks before your last frost date and you'll lose the seedlings to a cold snap.
This reference guide consolidates those critical numbers for the most common vegetables, herbs, and annual flowers into one lookup-ready resource. Use it at the potting bench, tuck a printed copy in your seed box, or save it on your phone. Think of it as the foundation layer — once your timing and spacing are right, everything else, from watering strategy to soil amendment, builds on top of it.
| Cool-season sowing window | 4–6 weeks before last spring frost (USDA cooperative extension general guidance) |
| Warm-season sowing window | At or after last frost date; soil ≥ 60°F (General horticultural practice) |
| General seed depth rule | 2–3× the seed's diameter (Standard seeding guidance) |
| Tomato transplant depth | Bury stem up to lowest leaves (Promotes adventitious root development) |
| Raised bed spacing reduction | Up to 20–30% closer than row planting (Applies to controlled, amended soil conditions) |
| Garlic planting season | Fall (4–6 weeks before ground freezes) (For most US growing zones) |
Planting Depth and Spacing at a Glance
The table below covers widely grown vegetables and herbs. All depths are measured from the soil surface to the top of the seed or root ball. Spacing refers to the distance between individual plants within a row; row spacing (the gap between rows) is listed separately where it differs meaningfully.
| Crop | Sow Depth | Plant Spacing | Row Spacing |
|---|---|---|---|
| Tomato (transplant) | Bury stem to lowest leaves | 24–36 in | 36–48 in |
| Pepper (transplant) | Same depth as nursery pot | 18–24 in | 24–36 in |
| Zucchini / Summer Squash | 1 in | 24–36 in | 36–48 in |
| Cucumber | ½–1 in | 12 in (trellised) | 48–60 in |
| Bush Bean | 1–1½ in | 4–6 in | 18–24 in |
| Pea | 1–1½ in | 2–3 in | 18–24 in |
| Carrot | ¼ in | 2–3 in (after thinning) | 12–18 in |
| Radish | ½ in | 2 in (after thinning) | 12 in |
| Lettuce (leaf) | ⅛–¼ in | 6–8 in | 12–18 in |
| Spinach | ½ in | 3–4 in | 12 in |
| Kale | ¼–½ in | 12–18 in | 18–24 in |
| Beet | ½–1 in | 3–4 in (after thinning) | 12–18 in |
| Onion (sets) | 1 in | 4–6 in | 12 in |
| Garlic (cloves) | 2 in | 6 in | 12 in |
| Basil | ⅛–¼ in | 8–12 in | 12–18 in |
| Cilantro | ¼ in | 4–6 in | 12 in |
| Parsley | ¼ in | 6–8 in | 12–18 in |
| Dill | ¼ in | 12 in | 18 in |
A general rule of thumb: sow seeds at a depth approximately two to three times their diameter. Very fine seeds — like lettuce and basil — are pressed just below the surface and benefit from a light covering of fine compost rather than garden soil. For transplants, err on the side of planting slightly deeper than the nursery pot, especially for tomatoes, which root along buried stem sections.
If you're planning a dedicated vegetable patch, Your First Vegetable Garden walks through site selection and bed preparation alongside these spacing principles.
Sowing Windows: Timing by Crop Type
Timing is inseparable from your local last frost date (spring) and first frost date (fall). The USDA Plant Hardiness Zone Map and local cooperative extension services publish these dates by region — always verify for your specific ZIP code before planting.
Last frost date
The average calendar date after which freezing temperatures are unlikely in your area. Used as the anchor point for scheduling warm-season planting. Verify your local date through your state's cooperative extension service.
Direct sow
Placing seeds directly into outdoor garden soil, as opposed to starting them indoors in trays or pots. Many root crops and large-seeded plants perform better when direct sown.
Thinning
Removing excess seedlings after germination to achieve the recommended plant spacing. Crowded seedlings compete for water and nutrients, so thinning is essential rather than optional.
Transplant
A seedling started indoors or in a nursery and moved to its outdoor growing location. Transplants give warm-season crops a head start but require a hardening-off period before outdoor planting.
Hardening off
Gradually exposing indoor-started seedlings to outdoor conditions over 7–10 days before transplanting. This reduces transplant shock caused by sudden changes in temperature, wind, and sunlight.
Row spacing
The distance between parallel rows of plants, distinct from within-row plant spacing. Adequate row spacing maintains airflow, allows access for weeding and harvesting, and reduces disease pressure.
Cool-Season Crops (Plant Early)
These crops tolerate light frost and prefer soil temperatures of 45–65°F. Sow or transplant 4–6 weeks before your last spring frost date, or in late summer for a fall harvest.
- Peas, spinach, lettuce, radish, kale: Direct sow 4–6 weeks before last frost
- Broccoli, cabbage, cauliflower (transplants): Set out 3–4 weeks before last frost
- Carrots, beets: Sow 2–4 weeks before last frost
- Garlic: Plant cloves in fall, 4–6 weeks before ground freezes
Warm-Season Crops (Plant After Frost Risk Passes)
These crops require soil temperatures of at least 60°F and cannot tolerate frost. Transplant or direct sow on or after your last frost date, once soil has warmed.
- Tomatoes, peppers (transplants): Set out 1–2 weeks after last frost
- Squash, cucumbers, beans: Direct sow at last frost date or just after
- Basil: Transplant or sow after last frost; sensitive to cold nights below 50°F
Annual Flowers: Quick Reference
| Flower | Sow Depth | Spacing | Timing |
|---|---|---|---|
| Sunflower | ½–1 in | 12–24 in | After last frost |
| Zinnia | ¼ in | 6–12 in | After last frost |
| Marigold | ⅛–¼ in | 8–10 in | After last frost |
| Cosmos | ⅛ in | 12–18 in | After last frost |
| Nasturtium | ½ in | 8–12 in | After last frost |
| Sweet Pea | 1 in | 6 in | 4–6 weeks before last frost |
Before any seeds go in the ground, it pays to run through a bed-by-bed readiness check. The Spring Garden Readiness checklist helps you confirm soil prep, tool condition, and timing alignment before sowing begins. And once you know what you're planting, consider companion planting principles to make the most of your spacing decisions.
Adjusting for Raised Beds and Containers
Standard spacing guidelines assume in-ground, row-based planting. In raised beds and containers, you can often reduce spacing by 20–30% because the soil structure, drainage, and fertility are more controlled. This is especially true for compact crops like lettuce, herbs, and radishes.
However, avoid the temptation to over-plant. Even in a well-amended raised bed, squash and tomatoes need their full spacing allowance because their canopy spread — not just root competition — affects airflow and light. If you're weighing whether raised beds suit your goals, the trade-offs involved are worth reviewing before you build.
The broader framework for managing your garden across zones and seasons is covered in the complete seasonal care guide, which pairs naturally with the reference numbers above.
