20 Tips and Tricks for Successfully Watering Potted Seedlings

Your seedlings will have three main stages that affect how you water them:

1. germination
2. early sprouting and first leaves
3. true leaves and general growth

Their watering needs will vary according to:

• the above stages,
• type of plant,
• size of new seedling
• dimensions of pot,
• type of potting soil,
• overall humidity of climate
• overall humidity of greenhouse/indoor environment
• stage of hardening (getting used to being outside),
• weather while hardening

There are some basics:

1. Plant your seeds in pots filled with already well-moistened soil. This should be wet enough that it easily holds shape when you form a ball of it in your hand, but not so wet that your tray will end up with standing water. It is hard to get it perfect and I often end up adding more soil ingredients to the bottom of the mix to absorb extra water that settles there. Don’t fill the pots all the way to the top edge! You will want ¼ to ½ inch of space for future watering.
2. Once the seeds are in the pots (and labeled), give them one more easy watering, just to make sure the very top layer next to the seeds is wet and to help the soil settle in around the seed. Then cover with some sort of plastic. I use large plastic trash bags for most trays. They naturally capture a bit of air when they are put on and create a dome. If the seeds need light, I cover with clear plastic wrap. If they need dark, I make sure to use a dark plastic bag.
3. If your seedlings need light, you will probably need a grow-light set-up. Even if they don’t need light, some source of heat in the room may be needed to stimulate sprouting, depending on the time of year and the temperature dynamics of the greenhouse or room you are using. Since most greenhouses have quite a few windows, they tend to be colder than the rest of the house, even if it is an attached room.
4. The seeds can usually be left undisturbed and basically self-watering with this arrangement for three days, but you probably want to check after two days if you are new at this or in a new location. You will want to uncover them and get them light as soon as the sprouts show up. Note: I take the plastic off after three days even if the seeds haven’t sprouted yet. Otherwise there tends to be a problem with mold after that.
5. From now on check your seedlings or potential seedlings daily. In my environment, I only need to water them once a day until they sprout. Some of that will depend on how close to the top of the soil they are.
6. Think like spring rain as the seeds are sprouting, aka germinating. Most seeds like the constant semi-warm dampness of spring. As you can tell from the different times volunteers outdoors sprout, some like it cooler and some like it warmer. But they generally all like it damp. The seed absorbs the moisture and is activated according to the design within. Another aspect of spring rain is that it is usually not hitting in one place hard constantly. Having your nozzle on a mist setting and moving it around quite a bit can mimic spring rain nicely. There will be some variations on this, especially for distinctly warm weather plants, such as peppers, corn, and squash. However, with the exception of peppers, I usually direct plant most warm weather crops directly outdoors.
7. Some seeds need to be more soaked than others, but even for seeds that suggest pre-soaking, like passion vine, I find my method works without that extra step.
8. Seeds that are barely covered by soil or planted on the surface typically need to be watered more lightly to avoid washing them down into the cracks or moving them around in ways you would rather not (like if you are trying to get more than one seedling per pot in the beginning, to transplant later).
9. After germination, how you water will depend a lot on sprout size. However, since their roots are still getting established, they tend to benefit from a more constant supply of water. Don’t drown them, but don’t let them dry out.
10. Seedlings that are smaller and/or grow low to the soil probably need to still be watered more lightly to avoid having dirt wash over them or to keep them from being damaged by the force of water.
11. Seedlings that are taller or stockier can probably be watered with the more efficient shower setting now, but you still want to be careful to not wash the soil away from their baby roots. They need some time to form stable roots.
12. Once the seedlings are larger, their leaves can block water from hitting the pot. You might need to water larger plants from the side to make sure the water is going into the soil.
13. If the weather is already regularly warm enough, I will start setting out newly sprouting seedlings in the sun right away. Keep in mind that this complicates monitoring for water. The area I use is shaded by mid afternoon, so that moderates the sun for my seedlings.
14. Usually I am starting seedlings in my greenhouse when it is still too cold to harden them off regularly. In these circumstances, I have to start being more aware of not over watering. Once the seedlings have their first true leaves (usually their second set of leaves) they appreciate letting the soil get a bit more dry between waterings. Not bone-dry, but so that the soil about an inch down feels barely moist. I don’t check all of my pots every day, but I usually check some samples. You can also get an idea by picking up the pots and noticing their weight.
15. If your plants end up drooping now and then, don’t despair. At least try watering them and see if they spring back to life. If that happens too often, it might stress them out. However, I had some zonal geraniums that I grew from seed that were stressed out and small their whole first summer in pots. The front western exposure was just too much for them. I put them in the back yard the next year, where they got some later afternoon shade, and they grew to normal size. I overwintered them in the greenhouse for several years after that and they also bloomed in my greenhouse in the winter!
16. If the seedling leaves turn yellow, that doesn’t always mean lack of water to the pot. It might mean too much water is killing the roots, leading to the same symptoms as lack of water, because the plant now can’t get water through the roots. There is no substitute for feeling your soil and checking your trays for standing water.
17. Once you begin to harden off your seedlings outdoors, all of the above factors are magnified. In my experience, it is takes more supervision to keep pots watered appropriately outdoors. In the pots they have limited access to water and tend to dry out more quickly. Don’t forget that wind also dries them out.
18. Rain can be a mixed blessing. You have to consider the overall weather and the amount of water. I frequently bring my seedlings indoors if there is more than a sprinkle. It depends some on the age and size of the seedlings. If you do leave the out during a rain, be sure to check the trays for standing water that might lead to overwatering (or attract mosquito larva).
19. Before any transplanting, whether dividing seedlings, up-potting, or planting outside, try to give your seedling a solid watering a couple of hours before the event. This will help reduce the stress of transplanting. Also, give them a bit of a drink right after transplanting, too.
20. For bulbs, tubers, and roots I use similar watering methods. The main difference is that you don’t need to soak them the same way and they tend to get a little drier between watering from the start. I have started dahlia tubers this way for years. Last year I had great success with sweet potatoes.

Happy planting!