First up comes a little math. You need to figure out when your local last frost date is. This is just the date where it’s reasonable to assume that you won’t have any hard frosts coming to kill your tiny little plants. You can find your last frost date on the Farmer’s Almanac website.
Now, most seed packages will tell you when to start them early. The back will say something like “start indoors 6 to 8 weeks before last frost”. If you can’t find that information, google is your friend. Just search “when to start name-of-plant-here- indoors” and you’ll likely get some reliable information.
With that, you just count backwards from your last frost date. So for example:
Last frost expected April 30
Seeds need started 6-8 weeks early
Count back 7 weeks and check my personal calendar. Nothing going on a week before or a week after, so it’s wide open!
Now we think about the plant itself. Tomatoes get fairly tall and we don’t want to cut off the tops, so I would go with 6 weeks early rather than 8 weeks early. Basil, on the other hand, can (and should) be cut down shorter to encourage bushy growth, so that one I would start 8 weeks early rather than 6.
Now comes the gardeners common sense, something that wasn’t very common when I started gardening! If you have had a LOT of snow and very cold temps, add a week to your start date. The ground is going to be cold and hard to work in after a winter like that, even on the last frost date. If you are planting into raised beds, move that start date a week earlier because raised beds warm up sooner and can be covered with bottle tops or milk jugs to protect delicate seedlings transplanted out early.
If you aren’t sure at all, don’t move the date. You can always deal with a slightly too tall plant for an extra week before moving it outside!
Setting the Stage
When it’s time, you are going to want to prep over a garbage bag, a cheap shower curtain, or at least a sheet that you can shake outside and wash right away. I usually opt for the sheet, using the outside play one and shaking it out before washing it. Cover your work surface with whatever you’re using and lay out your seed starting trays or recycled containers.
Pour seed starting soil into each container, all the way to the top. I like to press down gently with my thumbs to pack it down a bit, then pour a bit more soil in. I don’t pack that second pass down, as you need some oxygen in the soil to nourish the seeds.
At this point, your containers should be in their tray or re-purposed plastic container. Gently pour water over all the containers, wetting them thoroughly. Water should come out the bottom at this point, you can lift up the corner of a tray to check. I usually let them sit for about 15 minutes here, then gently tip the tray to remove excess water from the bottom.
Finally, the best part!
Grab your seeds and start planting them! Each seed packet will tell you about how deep they should be. DO NOT press them to that depth, as you will be covering them with more soil. Instead, lay 2-5 seeds per cell/container depending on what you are growing. The smaller the seed, the more you can put in the cell. For reference, in a 1x1inch cell I’ll put about 3 spinach seeds in but about 6 thyme seeds in the same size space. You can always thin the seedlings out if needed, and lots of them transplant well.
Now, look back on those planting depths. Seeds will usually need to be planted as deep as they are in size. So a tiny little thyme seed will barely need covered with soil, but a hardy spinach seed will need a 1/4in covering. I use a scoop or old yogurt container to gently shake soil over the seeds, guessing at the depth of the soil. If you really want to, you can borrow a ruler from one of your kids’ backpacks and check, but I’ve never been precise with it and have pretty good success.
Now, this part is important.
You want to water the tops, but you don’t want to splash a heavy stream of water over it all. If you do that, you risk displacing the seeds you planted. I found that a sippy cup with the spill-proof plastic removed to be PERFECT for this. The water comes out in a slow, gentle stream and you can control just where it goes. Bonus, it costs you nothing if you have littles running around because you already have at least one of these in the cupboard!
(scroll to keep reading)
Pour water on them, just enough to wet the soil that you put on top because the soil beneath the seeds is already wet. After that, gently press down on the soil to ensure it is touching the seeds beneath it.
Cover everything up
Now, if you have a purchased tray, you’ll want to cover it with the lid that comes with. If you are makeshifting it, you’ll want to cover with your DIY seed starting tray cover. Either way, your lids stay on to retain humidity until your seeds germinate and little tiny seedlings appear. At this point, you’ll want to remove the lid/cover and start giving them supplemental water and, if using grow lights, extra light. They should not need watered during the germination time (which the seed is working on creating a tiny plant to push up through the soil) if the lid stays on and you gave it enough water to begin with.
I do not like to top water my seedlings, as they get pressed down into the dirt by the water. I usually will gently lift the corner of one of the containers and pour water into the tray beneath. I wait about 15 minutes, then carefully tip it sideways and drain any water remaining. You should check your tiny, adorable baby plants about once a day in the morning to see if they need water.
DO NOT WATER THEM TOO MUCH!!!
If you are one of those people who seems to kill every plant you come into a relationship with, it is likely because you overwater them. Almost all plants prefer for their top layer of soil to dry before being watered again. Seedlings can only tolerate a thin layer of soil being dry, because their roots don’t go very deep. As they grow, I let them dry out a little bit more and more. To begin with, waiting until the top layer turns a light brown is a good time to bottom water them.
A note of importance. Many seedlings will have the hull of their seed stuck to the top of the tiny new leaves. This is good! Do not remove the hulls in the hope of helping your plant. It actually strengthens the little plant to have that extra weight on it. The hulls will fall off on their own time and go into the soil to hang out, no work on your part needed. (You can see hulls stuck to the spinach seedlings in the top image of this post if you need a visual.)
The other big thing that happens when you take that cover off is the need for sunlight or supplemental light. If you are using natural sunlight, get your trays in that place that you identified as having the most direct sunlight. If you are using supplemental lights, get them down about 5 inches above the tiny seedlings. If you don’t have gooseneck lights for your seedlings, you can always prop your trays up with books and remove a book at a time as they grow and get closer to the light.
(Scroll to keep reading)
Some gardeners get their lights closer, but I prefer that 5-6 inch mark between lights and the top of my plants.
Your little seedlings will uncurl and start to push out their first leaves. These leaves aren’t actually leaves in the technical sense, they are cotyledons. These tiny leaves come from the seed itself and are there to start pulling in energy from the sun to help the seed develop its first set of true leaves.
At this point, you just keep lights on the plants for about 18 hours (if using grow lights) and check if they need water every morning. And, of course, check them every 4 minutes or so to see if they’ve grown more!
Now, once your baby puts out its first set of true leaves (so the second set of leaves on the stem) you will want to give it a little of that fertilizer we talked about in the last post. Mix according to manufacturer’s directions and then pour in the bottom of the tray with your water when you water next. Just pour the fertilizer mix in first, wait 10 minutes and see if any is left. If it is, leave it for about 5 more minutes then drain, if not add more water and let that sit for the 5 minutes before draining.
Depending on how intense you want to get with it, you can fertilize twice a week. I usually do about once a week for my babies, simply because it’s easy for me to remember that Sunday is fertilizer day.
I also start top misting at this point, usually once a day in the morning when I’m misting my houseplants. Just spray a fine mist over the trays. I pull mine out from under the grow lights to do this, but again it is totally optional. It makes me feel happy and I like to think my plants enjoy it too. Its a super fine mist and my plants are under grow lights, so it doesn’t contribute to mold or fungi growth.
If you’re growing basil or other herbs and they get too tall, you can pinch off the tops and plunk those tops in the soil to grow alongside the parent plant. You’ll end up with a super bushy plant!
The next thing you know, your plants will be all grown up and ready to move out of the house!