Vegetable Seed Calculator

Frequently Asked Questions

Why should I plant more seeds than the number of plants I want?

Germination is never 100%. Even quality seeds from reputable suppliers typically germinate at 70-90%. Planting extra seeds compensates for seeds that fail to germinate, allowing you to thin to the strongest seedlings and still reach your target plant count.

What is thinning and when should I do it?

Thinning is removing extra seedlings to give each plant enough space to reach its full size. Thin when seedlings have 1-2 true leaves. For carrots and beets where multiple seeds are planted per spot, thin to one plant per 2-3 inches. Thinning increases yield per plant.

Should I start seeds indoors or direct sow?

Tomatoes, peppers, and eggplant need 6-10 weeks of indoor growing before the last frost date and are almost always started indoors. Root vegetables (carrots, beets, radishes) do not transplant well and should be direct sown. Beans, peas, cucumbers, and squash can go either way but prefer direct sowing.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Not every seed you plant will germinate, and not every seedling that sprouts will be kept to harvest. This calculator accounts for both factors: germination rate tells you what fraction of seeds will sprout, and the thinning factor tells you how many seeds you will plant per final plant slot (to allow you to thin to the strongest seedling).

The core formula is: seeds to plant = ceil( (target plants x thinning factor) / germination rate ). Ceiling rounding ensures you never plant fewer seeds than needed to hit your target.

Germination Rate

Germination rate is the percentage of seeds from a given lot that will successfully sprout under good conditions. Most commercial vegetable seed packets list a tested germination rate on the label. Typical ranges by crop:

Radish, bean, pea: 85-95% (very reliable)

Tomato, cucumber, squash: 80-90% (good)

Pepper, beet: 70-80% (moderate - worth planting extras)

Carrot: 60-75% (lower - plant generously and thin)

Old or improperly stored seed: often 50% or less

Germination rates decline with seed age. Most seeds remain viable for 2-4 years when stored cool and dry, but always test old seed on a damp paper towel before committing a whole bed.

Direct Seeding vs Transplanting

Tomatoes and peppers are nearly always started indoors 6-10 weeks before transplant date and moved to the garden as seedlings. When you select these crops, the calculator sets the thinning factor to 1 because each transplant cell produces one plant and thinning is done in the tray, not the bed. The germination rate still applies to your indoor starting trays.

Carrots, radishes, beets, and most greens are direct-seeded into the garden. These crops benefit from planting 2-3 seeds per spot and thinning to the strongest plant, which is why their default thinning factors are higher.

Succession Planting

Rather than sowing your entire seed quantity at once, staggering plantings every 2-3 weeks spreads the harvest over a longer window. For a continuous lettuce harvest, divide your calculated seed quantity across 4-6 sowings. For beans and radishes, three or four successions of the same bed area can triple the effective harvest season.

Tips and FAQ

What if I have more bed space than plants needed?

Enter the bed length and spacing to see actual capacity. If the bed fits more plants than your target, you can either reduce your seed purchase or fill the extra space with a succession sowing.

Why does my seed packet say to plant more densely?

Many seed packet instructions are written assuming you will thin aggressively. This calculator lets you be precise about how many thinning seeds per spot you actually intend to plant, so you can match the packet instruction or be more conservative with expensive seed.

Frequently Asked Questions

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