When starting plants from seed, it is human nature to want to be cautious with the number of seeds planted. Gardeners naturally want to plant exactly the same number of seeds for the number of plants desired. I always thought the same thing too. I always wanted to save as many seeds in order to save money on buying more seeds for the next round of planting or even for next season. However, based on my experience of seed starting every year, I have quickly learned that my instincts were wrong!
So how many seeds should be planted per hole, cell, or pot? In general, two to three seeds should be planted per hole. Seeds do not have 100% germination rates, so not every seed planted will sprout. Overseeding holes, cells, or pots will help ensure that the number of plants you desire will grow (or more!).
Even after reading my recommendation of planting more seeds than necessary, you still may not be convinced. Maybe you’re thinking you want to save as many of your precious seeds as possible. Let’s read on to explore the reasons why over seeding is the best practice.
Why Should I Plant More Seeds Than I Need?
In order to explain the importance of overseeding, let’s walk through a real example. Here’s the situation: Let’s say you know you want a total of six tomato plants this year in your garden and you want to start them all from seed. If you get anything less than six plants, then you will be disappointed. This example will apply with any method you are using to start your seeds, either by sowing in cells, pots, containers or directly in the ground outside.
Not every seed will sprout. Seeds to do not have 100% germination rates. If you have a six cell starter tray for the tomatoes in the example and you plant just one seed per cell, you might end up with only four plants germinating instead of six. However, if you plant more than one seed per cell, you increase your chances of getting at least six plants.
Save space and seed starting mix. Let’s say you know you want six plants, so you think ahead and plant more seeds than you know you’ll need. This time you use twelve cells and plant one seed per cell because you know not every seed will sprout. Planting just one seed per cell is a waste of valuable space under your grow lights and also a waste of extra seed starting mix to fill those cells when you only plan on using six plants. If you put more than one seed in six cells, then you save both space and starting mix. Also, you will end up with the same number of desired plants! Below, we will learn about what to do with the extra growth!
Save money! We already figured out that we can save money on seed starting mix. This strategy will also save money because chances of not having to buy starter plants from a store if seeds fail are increased. Back to our example: If you want six tomato plants and you start just six seeds, then there may be a good chance that only four plants will grow. In this case, you’ll have to go to the store to buy two additional plants. Maybe you’ll just start two more seeds, but remember that this uses up more starting mix and time that you may not have.
If you want to save even more money on seed starting mix you can make your own and learn about in our article DIY Potting Soil and Seed Starting Mix to Save Money.
You get to pick out the strongest plants. Not every seed planted, even if it does germinate, produces a strong and healthy plant. Sometimes a “dud” or a plant that is slower to grow than the others grows. By overseeding, the gardener gets to pick out the best plant in each cell from multiple options, in some cases. This way, the six best plants possible are the ones that will be planted in the garden.
Increase your success the next season by using fresh seeds. Normally when I buy seed packs, even the smallest amounts available are way more than most home gardeners need. Who needs fifty tomato plants (especially of one variety)?! It’s tempting to only use six seeds and not waste all of those precious seeds, but remember, each year that passes, the germination rate of seeds decreases. In other words, seeds do get old – some more quickly than others. Chances of success increase by using fresh seeds, so there is no reason to be stingy to try to make one packet of seeds last multiple years!
Now that you have a better understanding of the benefits of planting more than one seed per hole, cell or pot, I will share with you some strategies sowing different varieties of seeds.
Examples of Sowing Different Varieties of Seeds
Herbs, Lettuce, Onions
Herbs such as parsley, oregano, mint, and cilantro are best to plant this way and they don’t even need to be thinned after the seeds sprout.
I plant lettuce this way because I like to use the “cut and come again” approach to harvesting my lettuce rather than trying to grow single large lettuce plants.
For onions, if starting indoors I use this method and densely plant them together. When they are ready to be planted outside, you can pull apart each onion plant fairly easily to space them out in the garden. Onion roots are pretty indestructible, so don’t worry about harming the plant!
Tomatoes, Peppers, Kale, Broccoli
When it comes to tomatoes, peppers, kale and broccoli, I would consider having medium sized seeds. When they are mature, these plants grow best individually – not together in clumps like the others mentioned above. For each of these types of plants, this is where multiple seeds should be planted per hole, cell, or pot and then thin them out. When the seedlings sprout and start growing, then thin the plants to one strong plant per “spot”.
Cucumbers, Pumpkins, Melons, Peas
Cucumbers, pumpkins, melons and peas have some of the largest seeds. In general, the larger the seed, the smaller amount of seeds should be planted in the same hole or cell. These types of seeds take up more space and grow roots very quickly once germinated. Multiple seeds can still be planted together, but I recommend not planting more than two seeds per hole with these larger seeds.
Now, you have learned how and why to overseed, but the next important step is to thin out those seedlings for optimal growth.
How Do I Thin Out My Seedlings?
Thinning out seedlings can be challenge for most gardeners. Planting seeds and getting them to sprout is hard work! Now, destroy/kill some of them! Ahhhh!! Yes it is hard for me to do too, but it is necessary – especially for the certain plants that need to grow individually and not together in a clump.
When seeds sprout, two leaves come out of the stem. These are called cotyledon. The next leaves that will appear are called the true leaves. They are true leaves because they will stay on the plant, while the cotyledon will eventually fall off on their own.
Around the time when the first true leaves form (or just before that time), it is time to thin plants to one per cell or space in the garden. Try to pick out the
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How long does it take for seeds to germinate? On average, most seeds will germinate in one or two weeks as long as conditions are optimal. However, some seeds germinate faster than a week and some varieties may take longer than two weeks.
What soil do I need for starting seeds? Seeds generally like to have a fine mix (no large chunks of material) for best germination. Seed starting mix is available at the store or
Do I need a heat mat for starting seeds indoors? While a heat mat is not required, it does help increase success for germination. Most seeds will germinate best at around 70 degrees F. Find the heat mat that I use here.
Do I need a grow light for starting seeds indoors? A grow light is not required if you have enough direct sunlight from a window. I find many people posting pictures online of their “leggy” seedlings next to a window, so I would highly suggest a grow light to start seeds indoors.