How Many Seeds Per Hole? The Germination Math

The Probability, Summarized

• Seeds per hole equals the number of plants you want divided by the germination rate — not a fixed number for every crop.
• At 80 percent germination, planting 1 seed per hole means roughly 1 in 5 holes fail to produce a plant.
• Planting 2 to 3 seeds per hole and thinning to the strongest seedling gets you closer to a full stand without wasting a whole growing season replanting gaps.
• High-germination, expensive seed (like some hybrid squash) is the exception where 1 seed per hole can make sense.
• Thinning removes competition early, before roots tangle, which protects the yield of the seedling you keep.

Seed packets rarely explain why they suggest planting "2 to 3 seeds per hole, thin to the strongest." It looks like wasteful advice until you run the germination math, at which point it becomes the obvious choice over planting one seed and hoping.

The Germination Rate Problem

Germination rate is the percentage of viable seeds that actually sprout under normal conditions, printed on most seed packets or available from the seed company. A packet marked 80 percent germination means, on average, 8 out of every 10 seeds you plant will come up. Plant exactly 1 seed in 20 holes at 80 percent germination and you should statistically expect about 4 empty holes.

The Formula

Seeds needed per hole to reliably get at least one seedling is calculated from the probability that all seeds in a hole fail: if germination rate is g, the chance a single seed fails is (1 minus g). The chance that n seeds all fail is (1 minus g) raised to the power n. At 80 percent germination (g equals 0.8), the failure rate per seed is 0.2. Planting 2 seeds gives a combined failure chance of 0.2 times 0.2, or 4 percent — meaning 96 percent of holes will produce at least one seedling. Planting 3 seeds drops combined failure to 0.8 percent, essentially eliminating empty holes.

A Worked Example: Beans

Say your bean packet lists 75 percent germination and you want 6 plants ÷ 0.8 (a safety-adjusted planning rate, since real-world germination often lags packet numbers) equals roughly 8 seeds needed across your holes to reliably get 6 healthy plants. If you're planting individual holes rather than a row, planting 2 seeds per hole across 6 holes (12 seeds total) with 75 percent germination gives a per-hole failure rate of 0.25 times 0.25, or about 6 percent — meaning roughly 5.6 of your 6 holes will succeed, close enough to plan around.

When 1 Seed Per Hole Makes Sense

Not every crop needs the multi-seed hedge. High-germination hybrid seed — some squash and cucumber varieties test above 95 percent — has a per-hole failure rate under 5 percent even with a single seed. Combine that with seed that costs a dollar or more per seed (some specialty hybrids), and the math flips: the cost of wasted seed from over-planting can exceed the cost of occasionally replanting an empty hole.

Why Thinning Matters More Than People Expect

Planting extra seeds only pays off if you thin promptly. Two seedlings sharing one hole compete for the same root volume and light from day one; left un-thinned, both often end up weaker than a single unchallenged seedling would have been. The rule of thumb is to thin once seedlings show their first true leaves (not the initial cotyledons), snipping the weaker one at soil level rather than pulling it, which avoids disturbing the roots of the one you keep.

Adjusting for Old or Poorly Stored Seed

Germination rate drops with seed age — most vegetable seed loses 10 to 20 percentage points of germination per year past its packed date, faster if stored somewhere warm or humid. A 3-year-old packet originally rated at 85 percent might realistically test closer to 50 to 60 percent. Run a quick germination test (10 seeds on a damp paper towel, count sprouts after a week) before committing your garden math to an outdated number.

Let the Odds Decide

Multiple seeds per hole isn't wastefulness — it's a direct application of probability to a crop with a known failure rate. Once you know your seed's germination percentage, the seeds-per-hole decision becomes a calculation you run once per crop, not a habit you follow blindly.