Vegetable Seed Calculator: How Much to Plant
Calculate how many vegetable seeds you need per row or bed based on spacing, germination rate, and desired yield.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Seeds = ceil((Plants x Seeds/Hole) / Germination Rate)
Total planting positions are calculated by dividing row length by plant spacing and multiplying by the number of rows. Seeds needed equals positions multiplied by seeds per hole, divided by the germination rate (as a decimal). This ensures enough seeds to achieve the desired plant population despite germination losses.
Worked Examples
Example 1: Tomato Garden Seed Calculation
Problem:Calculate seeds needed for 3 rows of tomatoes, each 10m long, with 60cm spacing, 2 seeds per hole, and 85% germination.
Solution:Plants per row = floor(10 / 0.6) + 1 = 17 plants\nTotal planting positions = 17 x 3 = 51 positions\nSeeds needed = ceil((51 x 2) / 0.85) = ceil(120) = 120 seeds\nSeed weight = 120 / 300 seeds per gram = 0.4 grams\nStandard packet (~2g) has ~600 seeds = 1 packet is plenty
Result:120 seeds needed | 0.4 grams | 1 seed packet sufficient
Example 2: Carrot Bed Direct Sowing
Problem:Direct sow carrots in 5 rows, each 3m long, 5cm spacing, 3 seeds per hole, 75% germination rate.
Solution:Plants per row = floor(3 / 0.05) + 1 = 61 positions\nTotal positions = 61 x 5 = 305 positions\nSeeds needed = ceil((305 x 3) / 0.75) = ceil(1220) = 1,220 seeds\nSeed weight = 1220 / 800 seeds per gram = 1.5 grams\n1 standard packet (2g = ~1,600 seeds) is sufficient
Result:1,220 seeds needed | 1.5 grams | 1 seed packet
Frequently Asked Questions
How many seeds should I plant per hole?
The number of seeds per hole depends on the seed germination rate and the crop. For seeds with high germination rates (90%+), one seed per hole is sufficient. For older seeds or those with lower germination rates (70-85%), plant 2-3 seeds per hole and thin to the strongest seedling after emergence. Large seeds like beans and corn are typically planted 1-2 per hole. Small seeds like carrots and lettuce can be sown more densely and thinned later. Always check the seed packet for germination percentage — it should be printed on the label. Seeds over 2-3 years old may have reduced germination.
What is succession planting and how does it affect seed needs?
Succession planting means sowing the same crop at regular intervals (typically every 2-3 weeks) to ensure a continuous harvest rather than one large harvest all at once. This is especially valuable for quick-maturing crops like lettuce, radishes, spinach, and beans. For example, instead of planting 60 lettuce plants at once, plant 15 every two weeks for 8 weeks. This approach multiplies your total seed needs by the number of plantings but provides fresh produce over a much longer period. Not all crops benefit — tomatoes, peppers, and squash produce over a long season from a single planting.
How long do vegetable seeds stay viable?
Seed longevity varies by species when stored in cool, dry conditions. Onion and parsnip seeds last only 1-2 years. Corn, pepper, and lettuce seeds last 2-3 years. Tomato, cucumber, and bean seeds can last 3-5 years. Radish and beet seeds remain viable for 4-5 years. To test old seeds, place 10 seeds on a damp paper towel in a sealed plastic bag and keep warm for a week. Count how many germinate — if 7 out of 10 sprout, the germination rate is 70%. Store seeds in airtight containers in a cool (40-50F), dark, and dry location for maximum longevity.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy