All About Seed Starting
Updated: Oct 25
Well, it’s that time of year!
The time when gardeners start to get the itch: the itch for planting, that is.
The snow and freezing temperatures are beyond getting old. We have a fully hashed out garden plan, and we want to get started already! Although it is still too cold outside to start digging in the dirt (the ground is still frozen solid after all), it’s not too early to begin digging in the dirt inside. It’s time to plant those seeds that we will eventually transplant out into the great outdoors. Once it has warmed up, of course. A lot.
Today we are going to talk about everything seed starting: why you should bother, what equipment you need (and don’t need!), when to start what and step by step how to do it. Let’s get started then…
So here in Calgary, we have a pretty short growing season. 114 days, give or take a few, each year. And it can be fairly chilly at the beginning and end of that growing season. All those vegetables and flowers that like hot climates and long summers (looking at you tomatoes) can’t hack it without a bit of help. We can extend the season by starting our seeds in the warm indoors long before the snow has fully melted. That means warm temperatures for germination, faster germination and 114 days to go from young plant to maturity, rather than from seed to maturity. That’s a big head start. In order to get ripe tomatoes, peppers, eggplants, melons and winter squashes, transplants are mandatory in our climate. It also means that baby plant seedlings aren’t exposed to nasty weather (like late frosts), pests and diseases or weed competition when they are small and vulnerable. And, once we do get those transplants out in the garden, they are at the exact spacing they need to be in for the long run. No thinning shoots or empty spaces left by seeds that didn’t germinate, just perfectly spaced plants.
Those are great reasons for planting transplants in our gardens once temperatures warm up, buy why should we make the effort to start our own seeds? Why not just buy transplants from the garden center? The biggest reason is variety! While a garden center may have 5 or 10 different types of tomato transplants, the seed department may have 10 to 20 different varieties of seeds. Go online and scroll through the offerings of a few seed companies and all of a sudden you have hundreds of options for tomato varieties. Seriously, hundreds. And that is just tomatoes. You can choose a variety that is super sweet, has extra vitamin C, that is huge, has amazing texture, ripens super early, has fancy stripes or is the perfect size for popping in your mouth as you wander through the garden. It is completely up to you.
You know what you won’t get when you start your own seeds?
Herbicide and pesticide residue,
E. coli or any other pathogens.
Last, but not least, seeds are so much cheaper than plants. There is an initial cost of equipment (see below), but $2 for a package of 100 seeds works out to big savings when compared to $4-$25 for a single potted plant. I am always up for saving money!
What You Need
There are only a few things that you absolutely must have to start seeds: a container, growing medium, seeds and water. Everything else is dependent on how fast you want to grow and how early you want to start.
Plastic trays and cell flats:
These consist of an 11”x 22” standard sized tray (often called a 1020 tray) with a plug flat that fits into it. The plug flat can have 48, 72, 148 or even 200 cells and always have drainage holes in the bottom. My favourite is the 72 cell size to start almost everything except big squash seeds (pictured on the left in the picture below). From there, I pot up to 4” square or round pots and, if required, 1 gallon pots. These are all cheap, standardized and reusable if sterilized each year. Some are made of sturdier plastic than others which will affect how long they last and their cost.
Biodegradable pots: Pots that can be planted directly into the garden are made of peat, coir, cow manure (called cow pots), DIY toilet paper rolls or newspaper pots (using a pot maker). These can usually be found in the same standard sizes as plastic pots and are an environmentally friendly choice (make sure you check that your peat is from sustainable sources!). In addition, plants have far less transplant shock when they get put out into the garden. Cons include having to purchase new pots every year and the time to make your own if you are going with newspaper or cardboard pots. In my cold climate garden, there is also an issue with many pots not breaking down quickly enough, reducing the ability of roots to break through the pot walls.
photo by Lee Valley Tools
These are the Lamborghini of plant pots, although they are not actually a pot at all. A specific soil recipe is combined and pressed into a block using a soil blocker. The blockers come in escalating sizes and leave smart holes in the tops of successive sizes to perfectly fit the previous size plug. Roots are air pruned and therefore never get root bound. It is a very slick system. However, they also have a large investment cost. Not quite as much as a Lamborghini but still significant. You also must make your own soil mixture with precise moisture content to keep the blocks together when first made.
Peat pots and recycled containers
There are numerous containers you already have around the house that can be used to start seeds as well. It sounds better if I call myself thrifty rather than cheap, right? They must have drainage holes in the bottom (or have drainage holes added by you) and they should ideally be at least 4” deep. You will also need a tray of some kind underneath to catch the excess water. Clam shells (like you get your berries or rotisserie chicken in) work very well. Solo cups are also a popular choice. Just remember, that no matter what you use, it must be sterilized each year before you start. That can be with hot soapy water or a sterilization cycle in the dishwasher.
You may have learned in elementary school that seeds have everything they need to germinate, and that is true. They don’t require any additional nutrients from us or the soil until they get their first true set of leaves (not the cotyledons or seed leaves but the next ones). That means they don’t even need actual soil to sprout. We can sprout seeds right on paper towel with nothing but water (most don’t even need light). That is why we start our seeds in germination mix or seed starting mix, instead of potting soil. These two soil mixes have great moisture retention to keep seeds in constant contact with moisture and very light texture to provide air to roots (they need to breathe too) and to make it very easy for roots to push through.
If your seeds are starting out in small plugs, a germination mix will be sufficient. Once our sprouts have developed their first true set of leaves, they are “potted up” into larger pots that are filled with potting soil. If you are starting your seeds in pots that are big enough for growth past the first true leaves, they need a bit of nutrition in the soil than germination mix provides. That means using seed starting mix to begin with, and then potting soil if they need to go into a bigger pot before going outside. Potting soil provides “big boy/girl” nutrients to our starter plants.
Germination mix: peat or coir mixed with perlite (to improve drainage) and vermiculite (to aid in water retention) Seed starting mix: 50% potting soil and 50% compost (optional to add 10% worm castings)
There is a lot of controversy out there about whether or not you need grow lights to start seeds. Let’s just clear that up, shall we? If you are starting seeds at the beginning of March or even April, the sun is very different than if you were to grow plants indoors during the summer. Not only is the number of hours of daylight much lower then, but the angle of the sun is much different too. For example, here in Calgary, the pepper plant I seeded March 1st and placed on a south facing window sill will get approximately 10 hours of daylight, but that daylight will be at an extremely low angle, a maximum of 30° from the horizon to be exact. What that means is that my poor pepper plant is basically getting crap for sunlight. He will most likely grow up with an overly long stem as he tries to reach towards the light. We call this legginess and it results in fragile, unhealthy seedlings.
Keep in mind: We do not want tall, skinny, supermodel starter plants. We like them short, stocky and sturdy. Think troll instead of supermodel!
For ideal growth, our plants need a minimum of 14 hours of good, direct light. The earlier you start your seeds, the less intense the light coming in through your windows will be, and the more helpful grow lights will be. The later you start your seeds in the spring, the less necessary they will be. It is a bit of a judgement call. Plants that are started early in the year will definitely need supplemental light. Those started around your last frost date or later (we’ll get to that in a bit) may not, if you have a nice south facing window for them. Don’t forget to rotate them!
What do I do? I have 3 grow lights currently that fit one standard tray underneath each. I start all of my seeds under these lights. When I run out of room for new seed trays, the bigger plants get moved to the sill of my south facing windows. It’s the best I can do with the room I have now and by the time I have to move my plants to the sill, they are usually large enough to not have to worry about legginess.
So if you have decided to go with some grow lights, which ones are best? If you want all the nitty gritty details about grow lights, I have a detailed article here (link coming soon). For starter plants, the most common lights are either fluorescents or LEDs.
Fluorescents are available as either T8s or the newer T5s (the number refers to the eighths of an inch in diameter of the tube). T5s are more efficient, slightly more expensive, have a shorter life span and put out more heat than T8s. If you don’t want tubes, you can purchase CFLs which screw into a common light socket. Fluorescents are relatively inexpensive and you can even use good old fluorescent shop lights from the hardware store instead of specific grow lights to save money (if you are using them for seed starts only). Just make sure that they are high spectrum (6500K).
LEDs are significantly more expensive, but last far longer than fluorescents. You will probably end up buying a new ballast before you need to put in new bulbs. They are very efficient, produce way less heat and are an environmentally better choice. Specialty “warm colour” lights (usually around 3000K) and super expensive HID lights are overkill and only needed if you are growing fruits or flowers (which we aren’t for seed starts).
There are a couple more things you will need to know about lights. Your young plants will need 12-18 hours of light per day (16 hours is a good average). A timer will make your life infinitely easier here. Your lights should also be 3-12” above your foliage for fluorescent lights and 12-24” above the leaves for LED lights. Having your lights on some sort of system that allows them to move up and down to accommodate growth will also make your life much easier.
A light summary: If you are starting early seeds, get a light. Go for LED if you can afford it, fluorescent if you can’t. Put your lights on a timer set for 16 hours/day and make sure the height of your lights can be adjusted as your plants grow.
A cover over your trays during germination keeps moisture and heat high. This is a good thing. If you have a standard tray, there are short and tall covers that are clear so you can see when things start to sprout. Otherwise, a clear plastic bag over the whole thing works great too. As soon as sprouts start to pop through the soil, TAKE THE COVER OFF! Leaving it on will lead to possible mold, mildew and fungus issues. That is not a good thing.
Heat mats allow for faster and more even germination of your seeds, but they are not mandatory. Whether or not you use one will depend on how much of a rush you are in, your budget and how cold a space you are growing in. They come in sizes ranging from window sill width to standard tray size to large table size. Make sure you get one that is specifically set for germination temperature or is customizable so you can make it that specific temperature. We are looking for 18-22°C for most seeds. That rules out heated blankets made for people by the way; those don’t work so well in wet environments. As with the tray cover, as soon as sprouts start to pop through the soil, TURN THE HEAT OFF! Additional heat will also lead to mold, mildew and fungus issues.
Plants naturally live outside, where they are constantly exposed to the movement of air around them. That movement helps them stay healthy. Wind stress on the stems encourages the plant to strengthen those stems, resulting in thicker, sturdier plants. Remember, we don’t want supermodels here. Air movement also diffuses humidity and keeps the top of the soil dry. All good things in reducing the incidence of mold, mildew and fungus (are you sensing a theme yet?). Even minimal airflow will work here. A small table top fan on low is ideal. Or, if you are feeling super frugal, get your kids to gently blow on your plants for 1-2 minutes a day. And don’t forget to rotate your starts every once and a while so they don’t lean to one side.
Water is one of the most important elements in plant growth. The absolute best way to water your plant starts is from the bottom. That sounds weird right? It makes sense though when you think about it. The bottom is where the water is needed: the root zone. Watering from the bottom also prevents the soil surface and seeds from being disturbed and moved around, especially when first planted. It also keeps the surface of the soil drier which, as previously mentioned, helps reduce the incidence of mold, mildew and fungus. Unsure if you need to water? Stick your finger in there! Embrace the dirty fingernails.
An easy way to water from the bottom: Place your plant containers (the ones with drainage holes) on a mesh tray and then set the mesh tray into your bottom tray (the one without the holes). Use a watering can to fill the bottom tray with an inch or so of water. Wait 10 minutes or so for the water to soak upwards. Lift the mesh tray, pour out any remaining water left in the bottom tray, and replace the mesh tray back in the bottom tray. Voila! Perfectly watered transplants.
Can’t really start seeds without the seeds, can we? Seeds can be purchased from garden centers, big box stores, the dollar store or online from seed companies. Wherever you get them, there are a few important things you need to pay attention to on that seed package. And if you want even more detail, I have a whole article on reading seed packages here.
When to start your seeds. Often given in relation to your average Last Frost Date (you can look up yours here) or as a date range.
How many seeds are in the package. Quantities can range from 6 to 500.
What year the seeds were packaged. Some seeds are viable for 10 years with no change in germination rates, some for only 1 year. We can often use leftover seed from previous years.
If the seeds require stratification (a cold cycle) or scarification (physical damage to the seed coat) to germinate.
If the seeds are heirloom, hybrids, GMO, open-pollinated, organic, determinate (bush type growth) or indeterminate (vining growth). Definitions can be found here.
Where the seeds are from. Seeds collected from plants grown in a climate similar to yours will be hardier and better suited to your environment.
Number of days to germination and number of growing days until maturity or harvest.
Price. Like most everything else, buying in bulk is cheaper. That’s one more reason to make friends with other gardeners and buy together.
How many seeds should I plant?
A good rule of thumb is to plant 20% more cells than you want plants out in your garden. That accommodates low germination and any plant deaths due to fungal issues, transplant shock, accidents or cats. In addition, I like to plant two seeds per cell if they are very small seeds, cheap seeds or seeds that have poor germination rates. Many seed packages will state the germination rate on them. Plus, extra plants to share are one reason that everyone loves gardeners!
When to Plant
The first thing we need to establish is when to stick those seeds in the soil. The seed package should let you know if you need to start those seeds inside and transplant them outside once it has warmed up. It should also specify when to start them inside. The number of days to maturity indicated on the package is from the time you plant the seed, if it is a seed you direct seed outdoors. If it is a seed that needs to be started indoors and transplanted, that number of days to maturity is from when the starter plant is transplanted outside.
For example, I purchased Black Krim tomato seeds (one of my favourites) from West Coast Seeds. The package says they mature in 80 days, to start them indoors mid-March to early April and that they need 6-8 weeks growth before transplanting outside once night time temperatures are 10°C or higher. So I can either seed them mid-March to early April or I can get out my calendar and count backwards from when I have warmer night time temperatures. In Calgary, those warmer temperatures usually happen early to mid-June. For this year (2020), let’s go with June 13 just as an average. If I count back 8 weeks we come to April 18th. The package also states that the seeds germinate in 7-14 days, which brings us a planting date of April 4th. If I am not using a heating mat to speed up germination, I may want to start those seeds even earlier, just to be sure.
The next thing we need to check is if that variety works with the number of growing days we have. No point putting all that time and energy into something that has no chance of us being able to eat it!
Calgary’s average Last Frost Date (LFD) is May 23rd and our average First Frost Date (FFD) is September 15th (find your dates here). That gives us an average of 114 growing days. If we transplant our Black Krim tomatoes outside around June 13th, that gives us 94 days before our average first frost. The package says we need 80 growing days from transplant to maturity. That is cutting it close, but is still doable.
Can you see why we need to find short growing season varieties here? Days to maturity are important! Many varieties of tomatoes, peppers, eggplants, melons, winter squash, cabbages and so on, just don’t have enough days to get super delicious before they freeze.
If your package doesn’t specify when to plant, there are a number of charts online that have timings. West Coast Seeds has a good one here. You can also check out my guide in Crop Planning: Part 2. Keep in mind the climate each chart is intended for. Florida has completely different timings to start plants than Alberta. For Calgary, a general guideline is to start seeds indoors:
Beginning of March for most perennials, peppers, parsley, leeks, onions from seed, pansy, petunia
Beginning of April for tomatoes, eggplant, broccoli, cauliflower, melon, cabbage, celery, fennel, basil, oregano, marigold, (kale, kohlrabi and lettuce can be started indoors at this time or direct seeded outdoors later)
Beginning of May for Brussel sprouts, pumpkin, (cucumber and squash can be started indoors at this time or direct seeded outdoors later)
How to Plant
There are just a few simple steps.
1. Get all your gear together first.
2. Fill containers or cells loosely with germination mix or seed starting mix.
3. Lightly tamp down soil. Another container of the same type works well for this.
4. Top up with additional planting mix.
5. Check package to determine depth at which to plant seed. Use the rounded end of a pen to make an indent of the correct depth in the center of the container or cell.
6. Drop 1-2 seeds into each hole. The number of seeds per hole will be a judgement call based on germination rate (found on seed package), size of seed and cost of seeds.
7. Sprinkle with additional planting mix to cover. Tamp down gently to ensure seed has good contact with soil.
8. Place container in tray and water from the bottom (see above).
9. Cover, turn on heat mat and grow lights if using. Remember to set the light timer for 16 hours/day.
10. Patience! Recheck the number of days to germination if you are starting to get antsy. 11. Water when needed.
12. Once seeds have sprouted, remove cover and turn off heat mat if using. Turn on your fan and your grow lights.
Don’t forget to label!
I know you think you are going to remember exactly what you planted and where, but trust me, you won’t. Plants get rotated and moved around and seed leaves give you absolutely no indication of what a plant really is. So make sure you label everything. I like to use a popsicle stick cut in half and an oil based Sharpie to write on it with. As I have said before, I am cheap. Popsicle sticks can be composted when you are done with them (don’t use them again, they can’t be sterilized) and oil based ink won’t smear or fade when it gets wet.
Care of Transplants
Photo by Pixaby
And finally, our little seeds have started to grow! As soon as you see growth, remember to take off the cover and turn off the heat pad, if using. The seed leaves, or cotyledons, are the first to appear. They look absolutely nothing like what a plant’s true leaves do (see the cilantro example at right). Plants have either two seeds leaves (dicots) or one seed leaf (monocots). Most of our garden vegetables and flowers are dicots. Most grasses and grains are monocots. Once the seed leaves are fully unfurled, there is one sad chore we need to do.
We start off by murdering some of our plants. Yep, some of them need to go. I’m really, really sorry but it does need to be done. Cells in which we planted two seeds may have two sprouts coming up (or more, depending how accurate we were at counting teeny tiny seeds). Once the seed leaves are fully uncurled, we need to make a decision on which seedling in each cell looks the healthiest. Take a pair of small, pointed scissors and snip all but one sprout in each cell right at the soil line. Keep the ones that are sturdy and strong looking. Don’t forget to eat the clippings! Those are microgreens, and people pay big money for those. So don’t toss or compost them, put them in your salad.
Why the heck do I do it that way? Many people will plant a number of seeds, not in cells but in larger trays. They then pull apart the sprouts and try to plant each one in new pots. Although this does save some room, there are some issues with this. First off, you are seriously harming the root system when you pull them apart, and those tiny sprouts have very delicate roots! That is also why we use scissors to cut the discarded sprout off at soil level. No damage to roots that way, unlike pulling the sprout out by its stem. We planted more than one seed in each cell for a reason. Often times there are low germination rates and by the time we realize that a seed didn’t germinate, it may be too late to start a new seed from scratch and have it mature in time. Having more than one sprout also allows us to pick the healthiest and best grower of the two. A little bit of not-so-natural selection for you. Selecting sprouts when the seed leaves are fully out, gives enough growing time for us to determine which is doing the best while also making sure discarded plants aren’t hogging any nutrients from our keepers.
After the seed leaves, the true leaves are the next to appear. These are the typical shape, size and physical appearance given to that particular plant. It is normal for the seed leaves to eventually brown and fall off as the plant matures. Once there are one to four sets of true leaves, our next job is potting up. Once again, when exactly this needs to be done is a bit of a judgement call. Obviously, you don’t need to transplant into a larger container if it is time for them to go straight into the garden. Some plants may need to be potted up more than once before mother nature has warmed up enough for them to go into the garden.
When to pot up
This guy is definitely ready be potted up.
Seeds have all the nutrients they need until their first true leaves come out. Germination mix has minimal nutrients, so if that is what you used to start your seeds, you will need to pot up into something with nutrients in the soil once those true leaves start to form. Most seed starting mixes and potting mixes have enough nutrients to last about 3 weeks before they start to run out. So three weeks after the first true leaves start to form, your plants should be potted up into a larger container with new potting soil (not seed starting mix). The exception is if you see roots poking through the bottom drainage holes, then pot up right away. Pot up again if another 3 weeks have passed in the new containers, or you see those roots poking out.
Whenever you pot up your young plants, it is important to be extra gentle. They are still babies after all! Make sure the soil is moist before doing any transplanting. This will greatly reduce any transplant shock. And most importantly, do not grab your seedling by the stem! This is the most fragile part of your plant and is the only way for the roots to transport water and nutrients to the rest of the plant. If you damage the stem, your plant is toast. Hold your seedlings by the seed leaves if possible (they will fall off by themselves later anyways). Some seed trays have cells that open up, exposing the entire root ball with soil and making it easy to lift out the whole thing. I like to use a fork (make sure it is sterilized!) to scoop out the roots and as much soil as possible. I also like to use one of the cells to make a perfect whole in the soil of the container that seedling is going into next. Like the picture here.
Other than watering and potting up your transplants there is really only one other chore before they are planted out. That is a little bit of pruning, or pinching back as it is called in herbaceous plants. Pinching back involves cutting off the top part of a stem just above a set of leaves. This encourages the plant to grow that set of leaves into new stems. We now have two stems instead of one. This results in bushier, multi-stemmed, shorter plants. Once again, we are going for trolls not supermodels.
Why pinch back our plants? -more leaves and therefore more to harvest if we eat the leaves, -more leaves also means more surface area to collect sunlight (more food for the plant), -more stems to provide spaces for future flowers and fruit, -pruning actually stimulates our plants to grow faster by removing hormones found at branch ends that counteract the hormones that stimulate quick growth found all along the stem.
A lot of people ask about fertilizing our transplants. Honestly, I never do. All the nutrition your plants need should be in your potting soil. So make sure it is quality stuff! And we are regularly potting up our plants so they never use up all of those nutrients. If you absolutely must use fertilizer for some reason, I suggest using fish emulsion, a kelp or seaweed based organic fertilizer or compost tea. And please use half the strength given on the package. These are baby plants after all. They need baby dosages, not adult dosages.
The only thing I ever add to my transplants is worm castings (worm poop to be vulgar) if I happen to have some lying around. I like to think of worm castings as probiotics for plants. Just like people probiotics it contains beneficial microorganisms that help your plants take up and use nutrients in their food. They just come from earthworm digestive systems. Sounds a bit gross right? We are just beginning to learn how beneficial probiotics are for people, but we’ve known for a long time how good earthworms and their poop is for our soil and our plants.
photo by MOA, Kenya via Plantwise.org
I have mentioned it a few times already, but the biggest problem people run into with starting seeds indoors is mold, mildew and fungal issues. The most common one of these is called “damping off”. This is a group of soil born fungal diseases that results in the stem of a plant rotting at the soil surface. The plant stem weakens and breaks resulting in death of the seedling. It spreads easily and quickly to other seedlings. If you notice browning or wilting of the stems near the soil surface, IMMEDIATELY move those plants away from all other plants. If you catch it very early, try spraying the soil and stems with cool chamomile tea. It can sometimes help. Other sprays to try include diluted tea tree oil, cinnamon oil, rosemary oil or grapefruit seed extract. If plants do not recover within a day or two, or you have caught it too late, discard your plants, soil and all. Sterilize your container before attempting to use it again.
How to prevent damping off -sterilize containers after every use (hot soapy water or sterilization cycle in your dishwasher), -use new soil every time you plant, -don’t over water and water from the bottom, -remember to take off the cover and turn off the heat mat as soon as you see sprouts poke out of the soil (fungus loves damp and warmth), -make sure there is adequate air flow such as a fan
Another common issue with seedlings is leggy, weak stems, or supermodel plants. Thin weak stems are easily broken and are insufficient for holding up lots of foliage. This is usually a result of insufficient light; either not enough hours or not the right intensity. It may be time to buy a grow light. Thick sturdy stems are also encouraged when stems are constantly stressed by things like air flow/wind. It may be time to think about a fan. A heat mat left on past the point of germination can also result in leggy stems from too fast growth. Make sure it gets turned off after germination.
Cats and toddlers: they can’t help it. Make sure you protect your plants sufficiently. Think in terms of large scale war defenses.
The last major issue that can occur with transplants is transplant shock. It can happen when potting up our plants into larger containers or when we transfer our plants out into the garden. It shows up as major wilting of the leaves and stems, often with bleached out or curled leaves. Sometimes there is leaf loss as well. The main reason it occurs is dry or damaged roots. The number one thing we can do to reduce transplant shock is to ensure the roots are consistently moist throughout the entire process. That means watering well before transplanting and making sure the process is done quickly and efficiently to reduce root exposure to the air. Once transplanting is complete, water well again. Being extra careful while transplanting will help reduce root damage too.
That’s it! You have successfully raised a plant from seed, nurtured it and are ready to set it free into the outside world. Like a child moving out for the first time, they will still need some attention from you, but Mother Nature will provide much of their care from now on.
Continue on with planting your starter plants outside in the next article on Transitioning Transplants to the Garden.
Yummy gardening everyone!
West Coast Seeds (www.westcoastseeds.com) for everything seed starting, seed sales and timing charts, etc.
Johnny’s Seeds (www.johnnyseeds.com) for everything seed starting, seed sales and gardening tools. Note this is an American company so climate information will be potentially different from yours.
Lee Valley Tools (https://www.leevalley.com/en-ca) for soil blockers, pots and other tools.
Stacey Murphy (https://www.youtube.com/channel/UCK8WWphD0zYS4c5jsLOOOmg) for lots of videos on everything to do with growing food.
Don’t forget your local garden centre or greenhouse!