As you get ready to plant seeds in a cell tray or directly in your garden, you may have noticed that seed packets often recommend planting multiple seeds in each hole and then down to one as the seedlings come out.
Many people wonder how many seeds they should plant together and if it isn’t a waste of seeds to put a few per hole only to sacrifice some down the line.
The answer boils down to each individual seed’s germination rate, and understanding how this works will help to ensure that your garden is full of as many healthy plants as possible.
How Many Seeds Per Hole?
It’s tempting to only plant a single seed per hole and not to use more seeds than are necessary and not have to kill any growing seedlings. But planting only a single seed will often leave you with empty spaces in your planter or garden plot where nothing sprouted.
The best way to avoid this is to put more than one seed in each hole.
How many seeds you should plant per spot will mainly depend on the germination rate for that plant, or what percentage of those seeds are expected to sprout.
Seeds never have a 100% germination rate, meaning that all the seeds you plant will rarely grow.
Peppers, for example, have one of the lowest germination rates of any vegetable, 55% for sweet peppers. This means that if you plant a single sweet pepper seed in each cell of a 72 plant starter tray, statistically, you’ll only get around 40 peppers to sprout (72 x 55%).
Each seed has a 45% chance of failing, but the more seeds you plant, the lower the probability of one of the seeds in that spot not germinating.
If you plant three pepper seeds per hole, there’s less than a 10% chance that they’ll all fail (45% x 45% x 45% = 9%).
Planting three in each spot also means that you’ll get around 119 pepper seedling (216 x 55%). This way, you can ensure that all your holes or starter tray cells will have a pepper plant growing in them.
It’s usually recommended to plant 2 to 3 seeds per hole, but you can use the germination rate information for an individual plant to calculate the optimal number of seeds for what you’re planting.
The germination rate for basil seeds is between 80 to 95%.
With basil and other herbs like dill, oregano, or parsley, you can either plant 2 to 3 seeds per hole and later thin down to 1 or plant multiple seeds per hole and let them all mature together.
You’ll get lots of smaller plants that may be better suited to constant harvesting of their leaves for your meals.
Germination rates are around 80%, so anywhere from 1 to 3 seeds are often planted per hole. Plant at least two to guarantee a high per-hole germination rate of 96%.
Germination rates of 55%. With carrots, you can plant 2 to 3 per hole or sprinkle seeds along the prepared row and later thin the seedlings to one every 3 to 4 inches.
With a fairly high germination rate of around 75% and medium-sized seeds, many gardeners will often plant a single seed per hole.
However, this still means that if you’re planting a single seed in each cell of a 72 plant starter tray, you may still end up with 18 empty spots.
With tomatoes, it’s recommended to plant at least two seeds per hole, raising your germination rate per hole up to around 94%.
When growing onions from seeds instead of bulbs, germination rates hover around 70%. Five to eight seeds per hole are recommended, raising your per-hole germination rate well beyond 100%.
Better still, you won’t need to thin your onions if more than one sprouts.
Simply plant the whole set together, and the bulbs will push each other out of the way as they grow. While you won’t get any giant onions this way, you’ll end up with a whole bunch of medium onions instead.
How Deep Do You Plant Seeds?
Planting a seed at the proper depth can help increase its germination rate and guarantee it survives long enough to become a little seedling.
Most of the time, a seed packet will tell you the recommended depth for that particular seed, but if you’ve lost the packet or are growing seeds you’ve saved yourself, you may be wondering how deep your seed should go.
While the depth at which you should plant a seed will be different depending on what you’re planting, a good rule of thumb is to plant a seed at no more than a depth of twice its width.
This means that a seed that’s 1/8th of an inch wide should be planted at a depth of 1/4 inch.
A larger seed that’s are half an inch thick should be planted an inch deep. Tiny seeds should be placed on the surface of the soil and gently sprinkled with some soil or vermiculite.
When planting multiple seeds in the same hole, you can’t really place them all together, especially if planning on thinning down to a single one.
For plants you’ll be keeping in a set, such as herbs or onions, you can place the seeds 1/8” to 1/4” apart in the same space or cell.
When thinning, space seedlings based on the recommendations of the seed package.
Small plants should be thinned to 2” to 3” apart, medium plants to 6”, large plants to 12” and extra-large plants like squash and melons to a few feet apart.
Understanding how germination rates work and how many seeds to place in a hole will allow you to maximize the space you have and your growing season in order to get the most production for your efforts.
Experimenting with the particular seeds you have will give you a good idea as to how many seeds you’ll need to plant during each season.