Seed Starting - After Germination
Seed starting - what to do after germination
In Part 1 we covered the seed starting equipment.
In Part 2 we covered how to start your seeds.
And here we are in the last installment to talk about what to do now that your seeds have sprouted.
What to do after your seeds sprout
Your tray should be under grow lights at this point either prior to the seedlings emerging, or immediately. When about half of your seedlings have germinated, take them off of the heat mat (if you were using one) and take the humidity dome or plastic covering off. If many still haven’t germinated, you can prop open the humidity dome before removing it entirely. The seedlings will need airflow to prevent things like mold and fungus problems, so remove it sooner rather than later. You can provide gentle air circulation with a fan. This strengthens the seedlings, and keeps growth of things like fungus and mold at bay. Also, if you leave seedlings on a heat mat for too long, it bakes the roots, and can lead to weak and leggy seedlings.
How long should the grow lights be on a day and how far from the plants
This will vary based on what you are using. If you’re using lights marketed as grow lights, you’ll likely be able to find this information in the product description. If you are using fluorescent lights, a general rule of thumb would be to have them on for 14-18 hours for veggies, and within a couple of inches of the top of the plants, without touching. The thing to note is how much heat they give off. They’ll need to be a bit further away if they produce heat. Make sure you are using lights that are suited to growing, not something like incandescent bulbs. Part 1 has a discussion about the minimum requirements to look for.
Watering
Use lukewarm or room temperature water to water your seedlings. Preferably filtered if you have city water. Some people recommend leaving water out for a day so the chlorine can evaporate, but this does not help with chloramine, which some municipalities add to the water supply. I use a brita filter, and use lukewarm water to fill it. Exposing the roots of seedlings to cold temperatures can shock them and inhibit the uptake of certain nutrients. If I'm in a rush I will use tap water though.
How much water? Up until they germinate, be very careful to keep them evenly moist. The dome will help with this and you likely won’t need to water them before removing it. Once they have sprouted, check often and don’t let them dry too much. You can let the top of the growing medium begin to dry, but if the pots start feeling light, it is time to water. Try not to let them dry out to the point that they begin to wilt. This will require checking on them frequently, likely a couple of times a day. If you have lights that generate more heat, and are using a fan, they will dry out faster. You can bottom water for the gentlest of watering, or apply water directly to the potting mix to avoid getting the leaves wet. To bottom water, fill the tray with water, wait a little while, and if there is still standing water, dump it out after the pots have sucked up what they need. Never keep your seedling’s potting mix saturated.
Fertilizing
In the seed starting equipment post, I mentioned that I like Espoma Start and fish fertilizer. These are both found at big box stores, nurseries, and online. They are liquid fertilizers that you add to your watering can. You should begin fertilizing your seedlings once they start getting their first true set of leaves. The first leaves after sprouting are called seed leaves, or cotyledon, and the leaves that emerge after that are the true leaves. The exception here would be if you're using a seed starting mix that already has fertilizer. Use a half or quarter strength dilution rate, especially if you’re using synthetic fertilizer. It is harder to over fertilize when using organic fertilizer, but it’s still a good idea to just give them a light feeding at the beginning. They don’t have high nutrient requirements at the beginning. If you’re diluting your fertilizer, you could potentially use it every time you water. As a general rule of thumb, you’ll be able to tell if your seedlings need fertilizer if they aren’t growing robustly and are turning yellow. Use the fertilizer water the ways mentioned above - either bottom watering or carefully apply to the potting mix.
Thinning
You can cull the smaller ones, like most people do, or you can fawn over each plant, and waste none. This is how I end up with triple or quadruple the number of plants I intend to grow every year. This is a personal decision, but mostly a practical one. A big consideration here is whether you have the space to accommodate the extra plants, and enough light for them. If you have friends and family that would like plants, you can share with them. I do still suggest at the very least to thin the weak, stunted, or diseased looking seedlings. Thin by snipping the seedling at the soil surface. Don’t try to pull it out, or you could disturb or damage the one you are trying to keep.
Up-potting
If you have started in containers large enough to accomodate the plant to be grown until planting it out in the garden, you can skip this part. If you have planted in small containers, or have done the dense planting method that I mentioned in Part 2, then you will need to transplant them to larger containers.
When to do this:
If you have several seedlings close together, you will want to do this when they have their first true set of leaves.
If it is a single seedling, do this if it has roots filling out the container and you still have time before you can transplant outside. If it outgrows its container and spends too much time like this, it can become root bound which will stress the plant out.
For tomatoes, you can plant them deeper into their new pot, so that the seed leaves are just above the dirt. The stem will form roots.
Troubleshooting
Leggy seedlings
My sprouts look thin, tall, and not very happy, what do I do?
If your seedlings are leggy (also known as etiolated), it means that they did not have sufficient light and stretched to try to reach more. Too much heat can contribute to this as well. As soon as seedlings emerge, it is important to have them close to a grow light. Seedlings need ~14-18 hours of bright light a day (depending on what type of grow light you’re using). If your seedlings are already leggy, immediately increase the light. That may mean putting them closer to your grow light (usually within a couple of inches for grow lights that don’t put off a lot of heat). You can keep growing them and see if they strengthen. If it is something like tomatoes (or to some extent peppers), you can plant them deeper when you transplant them (either to a larger container or to the garden, or both). They will then grow roots along the stem and it will make them sturdier. This only works well for plants that have the capability to grow roots anywhere along the stem. If they have been growing like this for a few days, you may lose them, or they won’t transplant well. If they look really unhealthy, it is worth resowing your seeds as a backup.
Damping off
My seedlings sprouted, but then kind of got a pinched stem and fell over.
This is called damping off. It is a problem caused by pathogens like a fungi or mold that kill the seedling, usually in cool and damp conditions. It is easier to prevent this from happening, since if it strikes, it can kill many seedlings very quickly, and spread throughout your tray. Once your plants are past the seedling stage, they’re no longer susceptible to this.
Prevention:
Starting with clean pots and sterile potting mix (not garden soil)
Air flow. Take off the humidity dome in a timely manner and use a fan to circulate the air
Having your tray in a warm place with plenty of light will help your seedlings germinate quickly
Keep the seedlings dry. Bottom watering is the easiest way to do this. If watering from above, water the potting mix directly and avoid getting water on the stems and leaves
Don’t keep too wet
To prevent damping off from further spreading if you think you have a problem, make a DIY fungicide. Water your seedlings with chamomile tea or add a small amount of hydrogen peroxide to water (quite diluted) and water the seedlings with it.
Up-Potting
Do I need to transplant into larger containers before I put them out in the garden?
I have a discussion on pot size in Part 1 as well as above. Basically, if your plants are getting root bound and you are still a ways out from being able to plant them out in the garden, it would be wise to pot them up.
Poor germination
Help! My seeds didn’t sprout!
This could be due to many things.
The growing medium could have inhibited germination if it was too chunky, or if there was too much nitrogen in it.
Your seeds could have been planted too deeply.
They could have dried out at some point, even if only briefly.
Poor quality or non-viable seeds. If you are using seeds sold for this growing season and they haven't been exposed to moisture or extreme heat, this shouldn’t be a reason for seeds failing to germinate. It’s not out of the question though- there was one supplier I bought seeds from where multiple packets had no germination in the same year I purchased them. If you are using seeds from years past, there are a couple varieties that lose viability quickly, like anything in the onion family and spinach. If you stored your seeds somewhere they could have been exposed to moisture or heat, this could impact their viability. Do not store somewhere like in a garage.
They may need a little more time, especially if you aren’t keeping them at their optimal soil temperature for germinating.
If you think they are not going to germinate, you can sow more seeds as back up, hopefully having identified the reason they may not have sprouted.
So there you have it! Hopefully after reading this three-part series, you learned a little something that will help with your success. Let me know if you have any other questions. Happy seed starting!
