February 13, 2020
Here it is mid-February already and I'm listening to the wind howling outside. As I look to the north I see some pretty nasty looking storm clouds. To the south, just a leaden, gray sky. It's hard to believe it's nearly time to start seeds for this spring's planting. Of course, if you're growing completely inside, it can be time whenever you choose. Since I run a mix of indoor, greenhouse, and outdoor planting I am pretty much working with something all year long. For the purposes of discussion, I'm going to assume outdoor planting.
Different seeds (plants) have different requirements for germination and growing the seedlings in order to get them ready to transplant outdoors. There are many things to consider before starting seeds. First off, you'll need to find a location to put your flats (flats are the trays that you'll set the pots in) where they won't be disturbed and possibly damage the new seedlings. There are a lot of things that can disturb your flats. Being moved constantly is probably the most common. Moving the flats to various locations, for whatever reason, disturbs the seeds or seedlings and changes the micro environment they're trying to grow in. Not to mention the opportunity to drop the flat. The worst disturbance I've found is my cat. When she was younger, she really enjoyed digging in all of our flowerpots, anything with dirt in it. So put your flat in a place where it is out of the way, doesn't have to be moved, yet has easy access for watering. When choosing your location, you'll also want to make sure that you aren't near anything that can be damaged by water or spilt soil. Inevitably something gets spilled. That's just the nature of gardening. I'd stay away from white carpet.
Timing is the next critical item to consider. Nothing should be transferred outdoors until after the last expected frost. In Laramie County it's safest to plan for planting after the first of June. Unless we have a crazy year like 2019, that's usually a pretty safe date. Check your seed pack for the germination time and the anticipated time to transplant. The packet will normally say something like "Germination 7-14 days" and "Transfer at 6-8 weeks". Understand that these are general times and your time will most likely vary somewhat. Sometimes they vary a lot. I started some borage seed a few weeks ago. The packet said 7-14 days and I had borage coming up in four days in half of the pots. The next four pots were one to three weeks later. Herbs traditionally have a lower germination rate than other plants so having to wait isn't necessarily an unanticipated problem. Some herbs only have a 10 percent germination. You may even have to replant some of the pots. To determine when to start your seeds, count backwards from the start date using the germination and transplant times to determine when to start the seed. In the previous example you would consider starting your seeds at 14 days + 63 days = 78 days prior to June 1st. Or about mid-March. I suggest always using the longer times just to be cautious. Then count back seven more days for the transition (hardening off) to the outdoors. To harden off your seedlings, take them outside during the day (after any chill is out of the air) and set them in a sunny location that is protected from the wind then bring them in at night. Do this for seven days before transplanting. That will give the seedlings time to adjust to the new environment and reduce transplant shock. A tip for moving your flats. Place a board under the flats so it doesn't bend double when you pick it up. They are notoriously weak and flimsy.
Some seeds have special requirements to start. There are many seeds that need to go through a winter in order to grow. You can simulate winter by freezing the seeds for a couple of weeks in the freezer. For these seeds, you can even store extra seed in the freezer even though most seed stores best in the vegetable drawer of the refrigerator. Some need to be soaked in water overnight to soften the exterior covering of the seed and activate the germination process. This is easy with larger seed. With small seed, not so much. Other seeds need to actually have the exterior covering scratched or scored before they'll germinate. These are usually the really hard seed. The scoring simulates being roughed up in the soil in their natural environment. I just use two pieces of 220 sandpaper with a sanding block. Lay one piece of sandpaper flat and wrap the other around the sanding block. Place the seed on the flat piece of sandpaper and rub the sanding block over the seed. The seed will roll around so you'll have to check it often to make sure it's scored but not rubbed through.
You'll also need different size pots for different plants. I start most of mine in two inch pot and up-size if necessary. But some things, such as vining vegetables, I start in three or four inch pots. If you think you may need to up pot (transplanting to a larger pot) remember to make sure you have sufficient space to put the larger pots. Most commercial potting soils advertise having enough fertilizer (and the right amount) to last for several months. Don't count on it. Sometimes they will but often not. Until the new seedlings have their second set of leaves they have sufficient nutrients to grow. After that time you'll have to pay attention to them to see if they are getting enough nutrients to continue healthy growth. A few weeks ago I mentioned a new mix I was trying, 50 percent native soil mixed with 50 percent compost, then mix that with about 10 percent vermiculite. The amount of vermiculite can vary to lighten the potting mix. I've had very good results with it so far. Cover your seeds to help keep the soil from drying out. The cover will also raise the humidity in your "mini greenhouse" which is a good thing.
Lighting and temperature are critical. Before germination, your pots can remain in the dark and it won't matter much but the soil temperature needs to be maintained between 65 and 80 degrees for good germination. As soon as the seeds start to germinate, they need light, a lot of it, 14 to 16 hours a day. Grow lights of some sort are the best way to provide light. To buy a commercial grow light is very expensive. A 2x2 light can cost upwards of $600. For most people, you can get by with an LED shop light. Get the brightest LED you can find and place it two to four inches over the tops of the seedlings. Set it up so that you can raise the light as the plants grow. If your seedlings become tall and spindly- looking, your lights are too far away. And remember that you may need to add nutrients as the plants grow.
Some seeds are directly sown outdoors, but the June 1st date is still valid. Just follow the directions on the seed packet and you should get a good healthy crop of whatever your are planting. If you have any questions, ask a Master Gardener. It's what we do. Happy gardening!