Starting Plants From Seeds – Tips To Ensure Success
Note: I’ve now started selling the organic fertilizers and microbial inoculants mentioned in this post. You can read more about that here.
You can get the jump on spring by starting plants from seeds.
Some plants pretty much need this, especially heat-loving plants like tomatoes, eggplants, and peppers being planted into cooler climates.
A few others such as carrots and squash really dislike being transplanted, so it’s best to directly sow them in the garden when the time is right.
For the rest, it’s up to you whether you’d like to get a head start by starting seeds indoors. 
I actually have a couple of trays going right now in order to test the germination of some of my saved seeds and to test some new seed sources of perennial greens I’m going to be growing. I’ll harvest all of these next month and then start seeds again for the garden.
It’s best to start most vegetable seeds 4-8 weeks before your last frost date in the spring, which you can look up here for U.S. cities and here for Canadian cities, or you can search online for your city/country.
The last frost date in Toronto, Ontario is May 9, while the date in San Antonio, Texas is Feb 28.
That means for many of my readers, the time to start planting seeds indoors will be somewhere between early January and early April.
And if you’re new to starting seeds, it’s great to do a practice run to get comfortable with the process, because it takes a bit of experience to get good at it.
You can also continue starting seeds indoors throughout the year, to be moved into the garden gradually as you harvest the early stuff.
Containers
For containers, I prefer multi-cell trays, rather than seeding all in one tray and separating later.
That way I can move plants directly into the garden when ready, rather than making extra work and disturbing the roots twice by potting them up, but that’s just my preference.
Put those trays into another big tray to catch water, and have a dome for placing on top to keep it nice and humid in there.
Potting Mix
Most conventional commercial potting mixes contain chemical fertilizers and a high percentage of peat.
Those chemical fertilizers can cause various problems for the health of your plants.
The peat is mined from threatened, slow-growing bog ecosystems, is very difficult to wet once dried, and holds water so tightly that roots can rot when it’s saturated.
So I don’t tend to use it much, but I also don’t mind if you use a little because it does seem to help with germination.
And for most people who want to start simple, I do recommend buying organic, chemical-free potting mixes, perhaps certified on the package by the Organic Materials Review Institute (OMRI), most of which do still contain peat.
If you’re doing a lot of starting plants from seeds, you’ll save money by making your own. There are all sorts of recipes out there, but I keep mine simple.
I make my potting mix from approximately equal parts screened compost, course sand, and good soil. Sometimes I’ll add perlite if I feel the mix needs lightening up so it doesn’t get too compacted.
The advice is often to make a sterile mix, but I don’t do that because creating a biological void invites opportunistic organisms.
Instead, I introduce the organisms I want, both in high-quality compost and a touch of effective microorganisms.
Light And Heat
When starting plants from seeds, you’ll need a place with at least 8 hours of direct sun each day.
But that can be difficult, especially in the winter, even with south-facing windows.
Because of this, it makes a big difference to have an additional light source – simple fluorescent lights in approximately the 6000 Kelvin range, suspended 6 inches above the foliage. I leave them on for 12-14 hours a day.
In the video above, I just used one 24″ length light above one tray. In the photos on this page, you can see I have four 48″ lights above two trays, which gives more balanced light across the width of the trays.
If you’re sticking with just the original light source – the sun galloping across the winter sky – you’ll probably need to rotate your plants so they don’t incline in one direction towards the light.
Rotation is a bit unnatural for them, but it’s better than having them all permanently leaning like a dog with its head out the car window.
You’ll also benefit from supplemental heat when growing plants from seeds, especially those plants that originated in warmer climates like many of our annual vegetables, especially if your trays are sitting beside a cold window.
Soil temperature makes a huge difference for germination, so it can be worth spending a bit of money for a heat mat, but again, it’s not usually necessary.
Soaking seeds
It takes time for seeds to wake up once you plant them – anywhere from a couple of days to several weeks, depending on the species.
You can give your seeds a head start by first soaking them for 6-12 hours in a solution containing sea minerals and/or liquid kelp.
These organic fertilizers stimulate plant growth and health, and help them deal with stressors. The water activates germination.
After soaking and draining my seeds, I sprinkle some mycorrhizal fungi on them, except those from the cabbage and beet families because they don’t form a mycorrhizae relationship.
How To Plant Seeds
Before planting seeds indoors, water the soil without saturating it completely.
When I’m watering, I also use my effective microorganisms, liquid kelp and/or sea minerals.
Seeds should be planted about twice as deep as the diameter of the seed, whether in the garden or in a tray.
Planting 2 seeds per cell will give you a better chance of getting something growing in each cell, and allow you to cut out the weaker seedlings once you can see which ones are doing better.
A spray bottle helps to keep the soil moist until the plants come up. You want to keep it moist until after germination, when you can let it dry out a bit between waterings.
When your plants are almost ready to go outside, you can “harden them off” by bringing them outside for a few hours during the day, gradually upping their time in the open air over several days before you set them free in the big wild world of your garden.
Do you have any questions about starting plants from seeds? Let me know below.
Once the seeds have germinated, should the heat mat be removed and room temperature lowered? I am getting mixed messages about this from various sources.
Technically, it depends on the type of plant. Tropical plants like warmer soils, so it can be left on. For my heat mat, it’s not as though it makes the soil all that warm, so I always just leave it on the whole time.
I have read that when seeds start sprouting to take them off the heat mat and take the dome off . Is this true ?
Definitely take the dome off to allow for air circulation, but if the plants are those that would grow in a hot environment, I leave the heat mat on.
Tks Phil, I look forward to more of your informative articles.
Where did you buy your light?
I bought it at my local fertilizer/hydroponics store, but you can get them online, including Amazon.
Is there any benefit to using mycorrhizal fungi in container plantings? The plants in containers won’t get the benefits of a root ‘network’ – but are there other benefits?
Absolutely – may even be more important in containers. Go for it!
Thank you!
Hi, I really appreciate all the valuable info you pass on to everyone. My question is what is the 6000 kelvin range on the light bulbs? Are they special plant bulbs and if so, where can I get them? Thanks again for your help.
Search for T5 fluorescent lights. Amazon has them, as do many other online shops, and local hydroponics shops.
Most of the vegetable plants in my garden grow in raised containers (4′ x 5′). Does this reduce the microbial activity? (There are no earthworms in the soil.)Thanks for all you useful information.
If the soil was brought in, there’s a good chance it has less microbial activity, but you can certainly increase that by using compost and microbial inoculants, and you can set up a thriving soil food web.
should I use water from the tap to start seeds
You certainly can, but it’s nice to let chlorinated water sit out for 24 hours so the chlorine can off gas, or if there’s chloramine in your water, you can add a bit of vitamin C to tie that up.
I wanted to participate in your survey asking whether I plant food or ornamentals. I thought of the property, with the veg. garden at the back, herb garden close to the kitchen door, the apple trees at the front, the new pear trees, the current, gooseberry and raspberry bushes by the chicken run and I decided to click on food. But then I remembered the flowers in the front garden, the circle garden with the lovely irises, the tiered garden, the day lilies by the mailbox, the columbine around the well-head, the poppies and shasta daisies in front of the barn, the containers by the front walk, and the lilac/bush rose and hydrangea bushes near the lane. The survey doesn’t allow for voting for both, so I thought I would just tell you my choice is both. We’re having another blizzard today, and more cold temps are forecast. Spring arrives next week, but we still have a deep snow cover (good for perennials, I know) and it’s hard to believe the calendar. My mental tour of the gardens, prompted by your survey question, has been a good contrast, and reminds me that this white landscape will change. Thanks for the lift!
Thanks for sharing Joyce! I love winter, but am definitely looking forward to tulips myself.
To water seedlings, what ratio of EM and Sea Minerals to water should I use?
If possible, I like to go with 1:500 EM to water, and 1:100 Sea Minerals to water. So that would be a little less than 1/2 teaspoon of EM and 2 teaspoons of Sea Minerals per quart of water.
I planted tomato seeds about 2 weeks ago. I have watered with sea-crop and BioAg. They are just now getting their 2nd set of leaves but the stems seem weak. Do I need to be feeding them something else as well or am I just rushing it?
It’s generally due to not enough light. Even if you’re using fluorescent lights, which seem bright to us, it’s not nearly as much light as they would get outside. My recommendation is to add more light and position it within a few inches of the top of the plants. As an aside, be sure not to overdo the Sea Crop and Bio Ag – they’re both excellent choices, just in small amounts.
Hi, Phil. I have 2 T5 lights on my seedlings stand however I still do see that my giant tomato plants which I have started just a week ago are making a long stem which obviously is the symptom of having lower than needed light income. Sure the both lights are Sunlight Fish& Grow T5 bulbs with single fixtures but they have a connector so they are both connected together in one shelve. The only thing I did not buy so far is the Nano Reflector which I’ve been told that is causing a tremendous increase of the light power, but it actually costs as another T5 body with the bulb (about 30CAD) in Montreal area, so I am a bit in question what would be the best decision. So far the distance between my self-watering plants and the light fixture is about 10 inch but I am afraid that if I lower it down, there would be too much heat.Oh, I forgot to mention that I have two heating pads but I did not used them so far as I’ve heard that they might generate sometimes more heat than needed and to kill the seedlings, so I was thinking about buying a thermostat but they are pricey too, so what is your opinion on that? Should I put a heat mat under, than on top a 10×20′ draining tray with another tray on top (72-128 cell) with drainage holes? If you say it would not overheat I would give it a try as it is something that I know my citrus cuttings would love to do.Btw, if you do a lot of seed germination, you might find a good idea to make yourself a light bulb stand from pvc pipes and fittings. I think that this is what I am going to do as it would come up about 10/15CAD but would avoid any risks of having the books fall down etc. And on top of that, the light would be hanging there on a chain or rope, so it would be easy to lower/higher the bulbs.I have never tried the ocean minerals but I have red tons of goods about it so do you think it would improve the growth rate too? I have lots of kelp in powder so I am making my own kelp extract (as well as spirulina and chlorella) but have no ocean next to me to try some of that water 😉
Lower your lights Milen – 4-6 inches above the plants. The reflector would also help. No need for the heat map though – that’s most helpful for germinating the seed. Kelp and ocean water are my favorite fertilizers – both are useful.
Thank you, Phil. I adore all your ideas and have implemented quite a few but it is a bit strange to apply some when our garden is our balcony and our “micro-farm” (with other words one of the rooms have been turned into a jungle 😉 ). I will make the light stand and try to lower the light and see where would that lead me and I guess there won’t be much of a heat when the bulbs are fluorescent. That might substitute the heat mat I guess, so it is all a matter of test&try.Thanks again,Milen
HI Phil can you please elaborate on what is ‘good soil’ in making your own potting mix?
I guess that could be a big discussion, but I just mean any purchased topsoil that looks/smells good and doesn’t have weeds growing through it, or any of the soil from your own yard that looks and feels like nice soil.I.e. Don’t take soil from the bald patch of your garden that can never seem to grow anything, and don’t buy topsoil that’s infested with weeds.
Hi Phil, nice info! One thing I hadn’t thought of was sterile soil inviting in the bad microbes. It has troubled me in the past about how on earth I should bake all that homemade starting mix to sterility. I’ve only been tinkering with the idea with starting seeds indoors for some years as I really don’t have a great place to do this. I may start small this year though on a table in the cellar which I have cleared off.Last year, I tried ‘winter sowing’ outdoors with recycled opaque milk jugs. Have you tried this? I had some success, but limited… I think mostly because I did not monitor them carefully enough in the spring. I plan to work on learning how to do this better as it seems like a great way to start seeds and have them sprout and grow when the time is right for them. Also, I think if I do it right– i.e. opening up the tops on warm days, then they will already be hardened off when I am ready to plant them out. I would like to learn to do both this and indoor seed starting as well.Thanks, Phil, for the seed starting video. Every bit helps clear up the mysteries! ;P
I don’t personally do winter sowing, but it can work. One thing to keep in mind is that once a seed starts germinating, it often needs some attention for the first couple of weeks, mostly water, so even with winter sowing, it still pays to keep an eye on them.
Hi Phil, It’s one month later and I had finally gathered all of my supplies in time to get some things started 4 weeks before our average last frost. (Thanks for the motivation to get it going this year!) I bought a four flat heat mat and a thermostat, organic seed starting mix and I used water from my fish aquarium with EM added (I hope not too much). That’s what I had on hand this time, none of the sea minerals or other stuff that you mentioned, this time. Everything has sprouted within 2 to 3 days and look very good! I have 12 kinds of tomatoes in one flat, herbs, flowers, various brassicas and peppers, etc in the other two flats. I still have room for one more. I am wondering about any possible challenges you may have found with mixing species of plants in one flat? Also, if I prick them out to move to 3.5 inch pots, there are sites that say, if the stems are leggy, you can plant them up to their first true leaves. One such site with the Royal Horticultural Society… but I thought you could only do this with plants that would develop adventitious roots such as tomatoes. I know you plant sweet potato slips deep as well, etc. but this web site did not specify any species in particular. Thanks!
Good job! There’s no problem mixing species in the same flat. I’m not entirely sure about deep-planting seedlings that don’t develop adventitious roots, but I don’t think’s an issue for most vegetables. More important would be to give them sufficient light to not get too leggy in the first place.
thanks so much. I think most of them are not leggy. I only have regular fluorescent light bulbs at this point and they are just barely above the plants, so I think that’s okay. the only ones that are very long and seem to be leggy are actually a vine; purple hyacinths beans. so maybe it’s because it’s a vine and not due to insuffficient light. Thanks again.
high altitude (7000 feet) short growing season, sometimes only 90 days… Have a grow dome and mini greenhouse to help me out outside. How early can I plant tomato seeds indoors to get tomatoes before the frost comes in the fall? I want nice big plants to set out in the grow dome….have a light inside too.
If you have sufficient light, I say you can seed them indoors as early as 8 weeks before you plan to plant them outside. That’s the max I would do. Choosing early-fruiting varieties will be key here.
Many organic gardeners are switching to coir (coconut hulls) as a sustainable alternative to peat moss. I have used this for several years and really like how it keeps the soil both light and evenly moist. I recommend about 1/3 coir in your potting mix.
Thanks Gigi, it’s definitely more sustainable than peat, but for those of us who don’t live where coconuts are grown, it still has to be shipped a long way. But yes, arguably better than peat.
Is an egg carton usable as a multi-celled planting tray, or are they impregnated with something?
Good question. I’m not sure about that.
I am setting my trays with tomato and pepper seeds on a heat mat to germinate. Do I need to also turn on my fluorescent lights over them before they germinate?
Light isn’t needed, but I actually provide it, partially because it adds more warmth, but also because it better mimics what would happen in nature. That being said, some seeds need a little light to germinate and other seeds can’t germinate with any light. Tomatoes and peppers seem to slight benefit from it.
2 questions. 1)my seedlings tend to get moldy. Am I watering too much?2) I started sunflowers indoors and planted them outside only to have something dig them up. Did I plant them too soon?
1. Maybe watering too much, or maybe you need more airflow (a fan will solve that), or a healthier soil food web (compost and effective microorganisms will help with that), or a lighter soil mix (compost and perlite will help with that), or all of the above.2. Not necessarily. Some animals like to dig up plants. You may have to protect the plants with a small fence or other type of cover.
After I put the dome on, do I still water everyday, or do I leave it alone?
Only water when the soil surface has dried out just a bit. We don’t want it to dry out too much, but we also don’t want to oversaturate it with water. You may only have to water 2 times per week. It depends on how much you watered in the first place, plus the heat and the humidity.
Thank you very much Phil. This is only my second year gardening, it is greatly appreciated.
My seedlings are doing well and have the first & second sets of leaves so I’m wondering how much fertilizer to use: I have Pacific Natural concentrated fish from the Organic Gardener’s Pantry. I use 4-liter size and I wonder if 2 tablespoons per 4 liters is okay or should I use less considering they are still under grow lights indoors. TIA.
Their suggestion is 2 Tbsp per quart for indoor plants, used monthly, but yes, using less when they’re so small is a good idea. I would do 2 Tbsp per 4 liters as you said, but every 2 weeks. Or 1 Tbsp per 4 liters every week.
Thanks Phil! I fed them yesterday morning. Thanks for sharing Symphony of the Soil with us!
I am in Florida and when I plant lettuce I have to keep it in the AC to keep it cool enough to germinate. I would prefer to keep trays outside. Any suggestions on keeping it cool enough to germinate outside?
I’m not sure how to keep it cool outside, but I do have a few tips to help with germination: Use green-colored, looseleaf lettuces because they often can take a little more heat; soak seeds for a full 24 hours before planting, in the sun for at least part of that time because sun helps them germinate; keep seed regularly watered after planting; provide some light shade for them with shade cloth or straw mulch or something else. Good luck!
I remember seeing the ratios somewhere but cannot find them now. I’d like to know what the dilution that you use to soak the seeds. Thank you!
1:100 for sea minerals and 1:50 for liquid seaweed.
Hi there…would like a reputable source to purchase organic seeds..thanks
That’s a good question. I’ve bought from all over the place but I’ve never kept track of germination rates or anything like that. Perhaps someone has posted a good list online, but my apologies, I haven’t come across it.
Hi, are any of the fertilizers you sell good for seedlings? And what would the dilutions be?
Thank you!
Both the kelp and sea minerals are excellent. I tend to use somewhere between a 1:50 and 1:100 ratio, which is 2.5-5 Tbsp per gallon of water. I soak my seeds for at least a few hours and then also water with the fertilizer every week or two after that.
Hi Phil, I was wondering if you use Humic/fulvic acid with the kelp. I’ve read that the kelp is even more affective when combined with the acid. Thx Ken
Yes, I do often use it. Here are the somewhat strange application instructions for the humic acids I sell ( https://www.smilinggardener.com/sale/mineral-fertilizers/#humic ):
The quality of humic acid products varies widely. This one is very good, containing over 90% soluble and contains a minimum of 85% humic acids.
Before application, first dissolve the powder in warm water at 5 Tbsp (1/3 cup) per quart of water. That quart will cover 2000 square feet, but doesn’t have to be used right away – you can store it.
When you’re ready to use it, mix that liquid with at least 50 times as much water, which is again 5 Tbsp (1/3 cup) per gallon of water, or 3 gallons of water for each 1 cup of the liquid.