Once you plant your seedlings, don't be surprised if you find yourself checking for signs of life repeatedly throughout the day. Be patient.
Germination times vary from plant to plant (look at your seed pack for days to germination). That time can vary because of the different environments in which the seeds are given to grow. To understand this, let's go over what exactly is happening that causes a seed to germinate in the first place.
When you place a seed into the soil, it is dry. So the first step in germination is for the seed to absorb moisture so the cells can expand and begin the process of respiration, which produces energy for cell building. That's why covering seedling trays and keeping the medium damp is ideal. The best practice for maintaining moisture at this phase is to use a spray bottle and mist the trays every day or two. How frequently you mist your trays depends on the humidity of the space you're growing in. If your soil dries out, your seed will too, and if that happens, your seed will die.
I personally find pre-sprouting to be a great way to go. This method involves placing the seeds between sheets of damp paper towel and then sealing that in either a Ziploc bag, petri dish, or any container that will hold in the moisture. You then place these containers in a warm spot and wait. As soon as you see the root start to emerge, plant your seeds.
Heat is another critical player in speeding up the seed's cell-building factories that are in high duty during germination and early growth. Heat causes everything to move faster, and seeds are no exception. For germination to happen, you need to have the right combination of moisture and heat. Most seeds have a range of temperatures at which they will germinate. Spinach, for example, will start germinating slowly at around 40F. But the ideal temperature for spinach germination is closer to 70F. I love knowing there is a range of conditions my seeds will sprout in because it takes some of the pressure off me doing it exactly right every time.
Once you reach that magical day when tiny green leaves start popping out of the soil, their needs begin to change. The first change is that they don't need it to be as humid. Optimal growing humidity is around 80% for most plants. That's why you should remove any cover over your trays once you see at least half of the seeds in the tray have germinated. Too much moisture can lead to fungal growth, algae, annoying little fungus gnats, and the death of your plants.
The next environmental change is light. Most seeds start their life below ground. Once they sprout leaves, the process of making energy through photosynthesis begins. If you are growing plants inside, you need to give them lots of light. Did you know that 12-14 hours of grow light exposure is equivalent to only six hours of direct sunlight? Grow lights do a pretty good job of matching the spectrum of light the sun gives, but it does not even come close to the strength. That's why seedlings need to sit close to the light for maximum benefit. You'll know your seedlings are too far away because they will become leggy.
You can identify leggy plants by how long their stem is compared to the leaves growing on them. They often become top-heavy and flop over. If you're growing seedlings on a windowsill, the leggy seedlings will start growing toward the light. The most common way to fix this would be to move your trays closer to the grow lights. Place them twice the distance from the light as the plant is tall. So if you have a one-inch tall tomato, place it two inches away from the light. For those of you growing inside without a grow light, rotate the trays regularly, and when temperatures are warm enough, put them outside for short stints (just like if you were hardening off to plant outside). You could even make an inexpensive cold frame or cover to hold in warmth. I start taking my spring crops out on days when the temperatures are around 50F and heat-loving crops when the temperature is closer to 65F. A few hours of sunning can go a long way in helping grow strong stems, green leaves, and ample roots. Set an alarm so you don't leave your babies outside too long or overnight, and be careful not to put them in direct sun right away. Too much sun can scorch your seedlings. I lost a tray of parsley that way three years ago. Whoops!
Another change in the environment once a plant sprouts is water. When a plant sprouts, it sends its baby root down in search of water, away from light. So put the water where the roots are. Get out of the habit of watering over the top and instead, water from the bottom. You can place water directly in the tray the seedlings are nestled in. If you don't have a tray, a cookie sheet works well for big trays, and tofu containers and other to-go containers are great for bigger pots. When you are bottom watering, be careful not to drown them. So after a few minutes of sitting, if there is still water left in the tray, dump it out. Roots need oxygen too.
Besides keeping plants hydrated, bottom watering also helps limit two common seed starting annoyances: fungus gnats and algae. Fungus gnats look a lot like fruit flies. The adult gnats are more annoying than harmful, but the larvae, which hatch in the moist surface of the soil, can feed on the roots. So by allowing the soil's surface to dry out, it reduces the habitat for those pests to multiply. The other annoyance is algae. It thrives in warm, wet environments and sets up residence on the soil surface like gnats. A little bit of algae isn't a big deal, but too much algae can be harmful. The algae will begin competing with the seedlings for water and nutrients. A simple house fan at a low speed not only helps dry out the soil surface faster, thereby removing the ideal pest habitat, but it also grows more vigorous seedlings.
The final step of seedling care I'm touching on today is keeping your seedlings well fed. When a plant sprouts, the first leaves that emerge are seed leaves or cotyledons. Those leaves provide the plant with all of the nutrients it needs to grow from the moment germination begins up to when the first set of true leaves grow. Seed leaves are often very simple in their shape and don't look anything like the rest of the leaves your plant will grow. Once the plant has grown its true leaves, that means it has also grown substantial roots below ground. At that point, the seed leaves have done their job, and it's time to start feeding your seedlings.
Seedlings don't need a lot of food to get going, but they do need something. When you grow seeds outside, they are nourished by the ecosystem they are growing in. The tiny critters in the soil constantly break down organic matter into forms plants can take up in their roots. The plants in turn release excess carbohydrates made during photosynthesis into the soil, which feeds the microbes. Symbiosis, baby! I'll explain more on that topic another day. When you grow plants inside, they have little if any nutrients available to them. Seed starting mixes are often made of sterile substances meaning they have no nutrients. And those with compost or vermicompost are in very small quantities that won't be able to sustain your babies until planting time.
So, here's what you do. Get a good organic liquid fertilizer and apply a half-strength dose once a week to your seedlings. Follow the instructions on the side of the product you use. I've had good results using Fish Fertilizer, but be warned. It smells. I find it has a similar stank to the fish sauce I use to make stir-fries and kimchi. It doesn't bother me much. My kids however are not fans. This is a good task to do on days you take your seedlings outside for some sunshine.
Before you know it, the ground is going to be warm in your garden and you'll be planting your babies in their new homes. Next up in this seed starting series will be information about thinning your seedlings and how to prick out plants to multiply your stock. And in a few weeks, we will be ready to transition plants outdoors and I'll share that process too.
I offer monthly or annual garden coaching packages if you would like a personal mentor to help you navigate your seed starting season. Email me at email@example.com, and I'll happily set up a free consult to see if it's a good fit for you. I would love to be your coach!