Seed Starting Part 2
How to start your seeds indoors for a vegetable garden
Welcome back! In Part 1 of the seed starting series, we discussed the benefits of growing your plants from seed, and the supplies that you need or are useful.
Now, we’re on to starting your seeds! I’ll give a quick rundown of the steps to starting seeds indoors, then I’ll go into the specifics.
Choose which seeds you’re growing. See Introductory guide to growing your own food Part 1 to help you think about which plant’s you’d like to grow. Figure out when to start them indoors.
Gather your equipment from Part 1 of the seed starting series
Moisten your soil. It should be like a wrung out sponge.
Choose which method you are using for your situation - if you would like to have one plant per container from start to finish, or using a dense planting method.
Mostly fill your pots with growing medium, just below the top of the containers to the proper level you’ll be planting the seeds. Alternatively, you can poke individual holes.
Sow seeds. If you want to end up with one plant, sow two seeds (three if you’re worried about germination). If you want several of a particular plant, sow that many plus a couple.
Cover with growing medium
Gently water
Cover with a humidity dome, put on a heat mat if you need it, and place under your lights.
Watch for the first signs of germination. When about half sprout, you can remove from the heat mat and remove the humidity dome.
Seed starting is a very individual process and you will find which methods you like best and suit your needs, and they may not be the same as mine. I start a lot of plants, so the dense planting method is what I favor. This won’t be the best method for beginners or if you want, for instance, two tomato plants or four different pepper varieties.
Space to grow
Before we get too far into the details of starting seeds, I wanted to take a moment to talk about some things to keep in mind when deciding how much to start indoors. This is a common mistake, and one that I run into in the years I am starting a lot.
Look at how much space you have to start seeds with good light sources. It is easy to get excited and start everything you want to, and then find yourself short on space under grow lights, especially if/when you up-pot plants into larger containers. Plan ahead and know the maximum number of trays you can have with your available space.
Something that can sneak up on you is “plant creep.” If you’ve planted multiples of each to make sure you get one that germinates, and you decide not to thin them but opt for planting each one in its own container, you might find yourself out of space or with not enough grow lights.
When to start indoors
When you start your plants indoors will vary by each individual variety you are growing. Most seeds have information on the back of the packet about when to sow indoors, or if it’s even recommended. It will say something like, sow 6-8 weeks before the last frost, and transplant in the garden 1-2 weeks after the danger of frost has passed. Here is a website that you can quickly see the recommendations for most plants by entering in your frost-free date.
Know your date of last frost
Which date should you use in the calculator? I recommend using the later end of the date range for the chance of the last freeze, which for those of us in most parts of the Front Range of Colorado (zone 5b/6a) would put us around May 8th-15th. So as an example, this would mean starting your tomatoes indoors the end of March to the beginning of April, and planting them in the garden at the end of May. In the article When to plant outside, I discuss how to actually determine when to plant out, but for the purposes of starting your seeds, a ballpark date will suffice.
Tip: Put your seed list and information on when to start in a spreadsheet, like Google Sheets. If you have just a few to keep track of, you can take notes in your garden journal.
For people that live in zone 5b/6a and have a date of last frost of mid May, this is a very helpful chart from Home Grown Food.
Common mistakes
The big thing to note here that can be seen by looking at the chart above, is that cool and warm season veggies have very different time tables for when to start indoors, and when to transplant. I see two big common beginner’s mistakes.
Starting all of the seeds at the same time, regardless of whether they are warm or cool season veggies
Starting veggies indoors that are best direct sown
A combination of 1 and 2 - starting crops that are easiest to start outdoors, too early indoors. They just won’t thrive, and unless you have a large space to keep planting them in bigger containers, they’ll get stressed waiting, and you’ll have to fertilize and water them potentially for an extended period of time.
The biggest consideration (e.g. for things like tomatoes and peppers) is after being adapted to growing indoors for so long, and potentially reaching maturity indoors (flowering and fruiting), they will undergo more transplant shock and either lose their fruit, or stall out and take a while to recover as they establish their roots and adapt to a different growing environment. Will they still grow well at later stages of the season? Almost certainly. But starting earlier rarely results in earlier harvest, it just slows them down when you transplant them. A juvenile plant has an easier time transplanting. Proper timing is key.
To summarize, the reasons to follow proper seed starting timelines and skip starting certain plants indoors:
Save yourself unnecessary extra work (hardening off, watering, fertilizing, planting in larger containers)
Avoid additional transplant shock for plants that have been started too early
Some plants don’t like their roots disturbed (e.g. peas, beans, root crops, squash, melons, cucumbers)
The ones that are better direct sown are fast growers anyway, and our growing season here on the Front Range is long enough for almost all veggies grown as annuals.
Planting methods
What size containers do I grow in? Do I start in small containers, and then transplant into larger ones before planting out into the garden, or start in the size that I will grow it in until planting out in the garden?
There are many things to consider with this, and a lot comes down to personal preference and how much time and energy you want to spend on transplanting.
How many plants are you going to start? If you’re starting a few for personal use, you can start in the size pot you will plant into the garden. As a general guide, think about the size of containers that you find the particular variety of starts in at the nursery. As long as you are starting in the proper time frame, this is an easy rule of thumb to follow.
If you choose something like an egg carton, or small cells to start plants in, this will not be a large enough size to grow most plants to the size that is needed to plant them in the garden. It could be sufficient for some types, like lettuce and some other greens, but not plants like tomatoes and peppers.
If you are starting a lot of plants, either for yourself or to give away to others, you can try the dense planting method. This is what I do, and I go into more detail on that process in the link above. This is an advanced seed starting method, so I do not recommend it if this is your first time starting seeds.
A benefit to starting them in the pots you intend to grow them in the whole time is that you won’t have to spend time transplanting them into larger containers.
Number of seeds to plant
It all depends on your needs, goals, space, and how much you have determined you can grow in your garden (Part 1 of the introductory guide to growing food). If you are just doing a couple plants of each type, you can start in the size pot that they will stay in until you plant them in the garden, and plant 2 seeds per container, 3 if you’re nervous about germination. This way, you will be sure to get at least one plant that sprouts in each container, and either thin to one, or if you have space or want to give away your extras, you could split them and pot them into different pots.
Two in each cell to ensure at least one sprouts. Transplanted to larger containers after they had their first set of true leaves
Planting depth
This information can be found on the seed packet or can be found online, but if you find yourself with a handful of seeds and no time to look it up, you can use this general guideline. Plant the seeds three times as deep as the thickness of the seed. Some need light to germinate and should be pressed into the surface. This includes lettuce, dill, and some flowers - these are ones that would self-sow in nature like columbine, poppies, and snapdragons. You don’t have to worry about this too much though if you’re just planting vegetables.
A simple way to sow your seeds is to fill all of your containers or inserts almost to the top, but leave a gap that accounts for the depth you’ll be planting your seeds. For example, if your seeds need to be planted at a depth of ¼”, you will fill your containers to ¼” from the top of the containers. This is shown in the photo above. Then, once you have laid your seeds in each container, fill by sprinkling soil on top (shown below). Alternatively, you can poke each hole individually to sow the seeds.
Watering
Water the seeds in after you plant them. This ensures the growing medium is making good contact with the seeds. Keep them evenly moist in the days leading to germination. It’s important that they are not soggy. Check out Part 1 of the series for my favorite early watering tool.
Keeping humidity and warmth in
Cover with a humidity cover of some kind. It could be a plastic dome, plastic wrap, or a clear lid that your repurposed container has. Once about half of the seeds have sprouted, remove the humidity dome. The seedlings will need lots of light and airflow.
Temperature to keep your seeds at
Different varieties of seeds require different temperature ranges to germinate, and have optimal temperature ranges. For instance, peppers will germinate between 65 and 95 degrees, but the optimum temperature is 85 degrees. Tomatoes germinate best between 75 and 80 degrees.
Whether you need a heat mat or not will depend on a few things.
Are they cool season or warm warm season veggies?
If they are cool season (think greens and anything in the broccoli family), you don’t need to keep them warm.
If they are warm season (think tomatoes, peppers, eggplant, squash), they will benefit from adding warmth. It will aid with germination, but is not strictly necessary.
What is your ambient temperature in the space you are growing them?
If it is warm or room temperature, you can get away with not using a heat mat.
If you are using a heat mat for your warm season veggies, you can take them off the mat when about half have sprouted. The seedlings do not need the extra heat and it can roast the roots. Bottom line, unless you are growing in a basement where it is cold, you don’t strictly need a heat mat. If you decide to use one, only use on the warm season veggies. What do I do? I use a heat mat for my peppers and tomatoes. With a heat mat I get germination in 3-5 days for tomatoes, and 5-8 days for peppers. Speeding germination is not necessary however.
Do I need to put them under grow lights before they’ve sprouted?
There are some seeds that need light to germinate, but most won’t care whether they have light before they’ve sprouted or not. You can have them under the lights just to be sure you don’t miss the window when they begin sprouting. It is critical to have them under a strong light source right when you see the first signs of the seedlings emerging. Even waiting a day could cause irreversible stretching. As a general rule of thumb, they need to be within 2 inches of the light source, as long as it is not hot. This may mean that you need more lights to cover all of your seedlings. This is an important thing to keep in mind when deciding how many plants you can start indoors.
Alright! So now that you know what to do, happy planting! Now it’s time to wait and watch for signs of growth. In most cases, you can find the estimated germination time on the backs of seed packets. Meet me in the last installment of the seed starting series, and we’ll talk about what to do after your seeds have sprouted. In the meantime, leave a comment below if you have any questions about sowing your seeds I didn’t cover.