Garden Primer 4 – Starting Plants from Seed

My indoor seed-starting setup
Tending to my seedlings last winter

With this post, my garden primer series transitions from the planning stage to the doing stage. I will be writing about what I’m actually doing in my garden as I do it, so if you’re in Zone 5-ish, you can probably follow along in your own garden! So, if you’ve been following along with this series, you’ve already figured out how much garden space you have, how many vegetables you want to plant, and considered whether you’d like to have a container garden this season.

Now it’s time to talk about starting seedlings. Whether you’re starting seeds in a couple of cottage cheese containers in a sunny window or hoping to start most of your vegetables from seed this year, the process is pretty much the same, and so are the benefits. Improved selection of varieties, a desire to know that your food was started in chemical and disease-free conditions, and the need to garden when there’s still snow on the ground are all reasons to start vegetables from seed.

Now is the time to start everything from basil and parsley to peppers, tomatoes, and tomatillos. And if you’re doing spring crops like Brussels sprouts, lettuces, broccoli, or cauliflower, these can be started now as well. I also start several annual flowers from seed for my cutting garden and container gardens, which saves money down the road and again, gives me more varieties from which to choose.

So first, you need to figure out where you should start seeds. Light is going to be key, so if you’re going to use sunlight, pick your absolute sunniest window, probably a south-facing one with not much in the way of trees or other houses directly outside to block light. I start seeds both in my sunroom, which has both south-facing and east-facing windows, and in the basement under fluorescent lights. You do not need special grow-lights–the inexpensive fluorescent fixtures you can pick up at the local big-box store will do just fine. Seedlings prefer 14-16 hours of light per day, which natural light does not provide at this time of year. So if you use a sunny window, you might want to consider some supplemental light for 3-5 hours per day. Just turning on the lights in the room does not help–the seedlings need the lights to be no more than 2 inches above them to replicate the intensity of the sun.

Remember that you need enough space not just for the tiny seedlings, but for the growing plants, which you will likely have to transplant into bigger pots at least once during the spring. Do not fill every ounce of space you have with trays right now, or you’ll have nowhere to put the plants as they grow!

Next, select and wash your containers. The experts will recommend washing your pots in a 1/20 bleach solution if you’ve used them before, but I have to admit that bleach grosses me out, and I’ve never had a single problem with disease after washing my pots in hot, soapy water. I use trays with 48-72 individual cells in them to start my seeds, but you can use any sort of container from yogurt cups to clay pots. Just make sure that you poke some holes in the bottom of the containers if they don’t already have them so that the roots don’t get water-logged when you water.

Then select a good quality potting medium. You do not just want a bag of topsoil–buy something that says it’s specifically for containers and/or seed starting. Most experts will recommend buying a soil-less seed starting medium (usually a mix of vermiculite and peat), and if this is your first time starting seeds, I would recommend it as well. However, if you can get through a couple of growing seasons without disease problems, you can probably save some money later on by buying a regular potting medium that is cheaper than soil-less mix, and also has some compost in it to feed the seedlings early on.

Now you’re ready to plant. I fill a 1.5 gallon pitcher to the 1-gallon mark with soil and then add water to it until it’s totally damp, but not dripping. It will take more water than you think to moisten the soil, and doing it first, instead of trying to water the cells after you have already planted seeds in them, will prevent washing the seeds away and/or not having enough soil in the pots. One gallon of moistened soil is about enough to fill 1 flat. When trying to estimate how much soil to get (which is never an exact science!), I have found that 1 cubic foot of soil (a regular-sized bag) is more than enough to do 5-6 flats of seeds. Remember that you will need more soil to transplant the seedlings, though.

Next, gently pack each cell or pot with soil. You don’t want to pack it like brown sugar in a measuring cup, but you do want to make sure that there’s enough soil in the cell to support your seedlings because that tiny bit of soil will hold all moisture and nutrients for your plants!

I usually take a plastic plant marker (which I re-use because I’ve had mold problems with the wooden popsicle-stick style plant markers) and poke a hole in the center of each cell. Planting depth for seedlings corresponds to the size of the seed, so a pumpkin seed gets planted deeper than a tiny broccoli seed. The rule of thumb is to plant seeds 2-3 times the size of the seed. So if your seed is a 1cm pumpkin seed, for example, you can plant it 2-3 cm (about an inch) deep. Gently recover the seed using the plant marker and then immediately write the seed type on the plant marker and stick it in the pot. It’s amazing how interruptions (in my case, curious children) can cause you to forget what you’ve just planted. Despite my best efforts, I typically end up with anywhere from one four-pack to a whole flat of “mystery plants” each season either due to me forgetting to mark something, mismarking it because I was distracted, or due to little fingers helpfully removing the markers at some point in the season.

OK, so what should you be planting now? Do not plant pumpkins now if you live in zone 5, or you will have a pumpkin jungle well before you can plant the seedlings out in mid-May. Do plant the following:

  • peppers (8-10 weeks before last frost date, which is May 10ish for most of Zone 5)
  • tomatoes (6-8 weeks before last frost date, but I plant heirlooms earlier because they seem to be more slow growing)
  • cole crops like broccoli, cauliflower, cabbage, etc. (4-6 weeks before plant-out, which is usually a month before last frost date)
  • herbs like basil, parsley, and cilantro (4-6 weeks before last frost date)

Most packets of seeds will provide a recommended seed starting date, so the above is provided just to give you an idea that it’s time to get going on seedlings if you’re going to start some.

Keeping the soil evenly moist is probably the most important thing you can do to ensure success with seedlings. If they dry out even once, they will likely die. It is also important to water the seedlings from the bottom instead of pouring water directly on to the seedlings. Not only can the rush of water bend or break a new seedling, but water can also wash tiny seeds away and splash fungal spores onto leaves, causing disease problems. This is why I suggested poking holes in the bottoms of any food containers you re-use for starting seedlings–that way you can place them in a tray and pour water into the tray, instead of on to the surface of the soil. If you’re using traditional seed flats, you can pull one 4-pack out of the tray, pour about an inch of lukewarm water in, and replace the 4-pack. You may have to water as often as twice a week until you get the plants potted up into bigger pots that can retain more water. The cells dry out quickly–try your best not to let them.

True leaves on tomatoes
A good example of true leaves on tomatoes. The "first leaves" are beginning to shrivel about an inch from the base of the plant.

When seedlings sprout, the first set of leaves they put out are not a “true” set of leaves. What this means is that they look and function differently than the “true” leaves. So when you read about seedlings and see references to report or fertilize when there’s X sets of leaves, make sure you’re counting true leaves and excluding the first leaves (see picture for an example). For example, you need to start fertilizing your plants with a diluted all-purpose plant food (I use seaweed) when they have two sets of true leaves, which will be 3-4 weeks after you plant, depending on the temperatures, amount of light, and type of plant.

First leaves on a poblano pepper plant
Tomatoes, peppers, tomatillos and some other vegetables have lance-shaped first leaves like the ones on this poblano pepper.

You may also have to transplant the seedlings around this time–when you start to see roots emerging from the bottom of the pots, it’s a pretty good indication that it’s time to repot. I typically pot veggies and flowers up into 2 1/4 inch pots that I have saved over the years from plants I’ve bought in nurseries. But you can use any container, as long as it’s bigger than the pot the seedling has outgrown, is clean, and has a hole poked in the bottom for drainage.

This tomato has both its first leaves and its true leaves
Note the difference in shape between the first lance-shaped leaves (the larger ones) and the true leaves (lobed)

Well, that’s enough to keep you busy for this week. I started my first round of veggies on February 21, and am starting another flat of annual flowers & herbs today, so you can bet I’ll be talking about transplanting seedlings here before too much longer. But while your seedlings are sprouting away inside, there’s plenty to be done to prepare an outdoor home for them, so don’t forget to check back often!

One thought on “Garden Primer 4 – Starting Plants from Seed

  1. Thanks Julie! You inspired me to try this for the first time. I know the boys will love to help me and it will be a fun project for us to do together.

    My only question is – the only south facing sunny window I have is in our garage, which is about 50-55 degrees. Is that ok? Also – how do you rig up your lights so they are 2 inches from the seeds? I’ll have to do something to get a flourescent light on them, but other than that, I think I’m good to go! So excited!

    Are those little seed packs in the major stores OK to buy? Or would you go with the local seed-and-feed stores the farmers use? Gfield has lots of those : )

    Miss you guys hope you are doing well! Hugs!

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