Starting Seeds Indoors – Seedling Maintenance and Care
If you read last week’s article on starting seeds indoors (The Complete Guide to Starting Seeds Indoors) and started some seeds of your own, then there’s a good chance you have seedlings that have emerged above the soil.
There is nothing better than seeing seedlings emerge after several days of patiently waiting and constantly checking, after all, everyone likes the feeling of doing something successfully. If you want these seedlings to survive long enough to eventually plant outdoors, there are a few things you will need to know in order to ensure your plants maintain good, healthy growth.
Light Distance and Temperature
When your seedlings emerge from the soil, one of the most crucial things you need to do is ensure there is a light source available for them – If there is no light when they emerge, there is a good chance they will stretch. For this reason, I recommend leaving lights on 24/7 to prevent seedlings from stretching and becoming leggy, which can have a significant impact on plant health. Once your seedlings have their first few sets of leaves, you can cut your light schedule back to 16-18 hours on, which is sufficient for most plants.
Here you can see the light’s distance from the seedlings
As I mentioned in the last article about seed starting, I like to keep my lights (T5’s) about five to six inches from the top of the flat when the seedlings first emerge. I keep my light slightly further than normal at this time to prevent the light from drying out the soil too quickly, as I have lost seedlings in a matter of just a day or two from this.
After a few days when the seedlings have established themselves and extended deeper roots, I will begin to lower the lights – around three to four inches from the tops of the plants is what I have found to be the best distance in terms of keeping plants short and not frying them. With good air circulation you can get your light as close as one inch from the top leaves like in the picture above.
Fans and Air Circulation
Another important factor in plant health is maintaining a good air circulation around your seedlings. Doing this will help prevent a local buildup of heat from your lights, which can cause a slew of problems such as drying your soil out very quickly, as well as causing heat stress to your plants – this is especially true if your seedlings are in an isolated corner or closet.
Use a thermometer like this one to monitor air temperature and humidity
For regular air circulation you don’t want to use anything too powerful for extended periods of time, as too much air flow can hurt the plants and stall growth. You want to choose a fan with a nice steady air flow that will provide fresh air without moving the plants much.
I like to use a few 120mm computer fans, as they are very quiet if you get a lower RPM model, and they also move a good amount of air. If you choose to go this route, you will have to cut the ends off of the fan cable and wire it to a 12 volt power source – I like to use 12v wall chargers, which can be found at most electronics stores or online for cheap. If you are not comfortable doing this, look for a small, low speed fan that already has a wall plug attached.
Here you can see a computer fan mounted to a piece of cardboard to direct air at plants
Occasionally you may want to use a more powerful fan to help encourage strong stem growth and harden the plant up a bit. To do this you can simply direct a more powerful fan towards your seedlings just enough that you can see them moving a bit, but not too much – In most cases you will want to deflect the air off wall or other surface to dampen it and it from prevent damaging your plants.
Watering your plants seems easy enough right? Well, you would think so, but most plants are killed by not watering correctly. Under water your plants and they will dry out and die; over water your plants and they will suffocate and die. One of the most common mistakes people make when caring for seedlings is over watering – you do not need to water your seedlings every day, and likely not even every other day.
A good indicator of a seedling getting too much water is green growth on the soil
There is no set amount of time for how often you should be watering, as there are many variables which can affect how often you need to water, such as air temperature, soil temperature, air circulation and the growing medium. The easiest solution to determine how often you should water is to simply monitor your plants, and record how long it takes for them to dry out.
When it comes to how to water seedlings, I have found it is best to bottom water – for this reason I put my containers in a 20″x10″ plastic flat for easy watering. By bottom watering you can ensure that water is evenly distributed throughout the soil by allowing it to be wicked up. Doing this will also keep the top of the soil from becoming waterlogged, while still keeping the underlying soil wet, encouraging deeper root development.
Bottom watering plants in a tray
If you choose to top water, make sure that the soil is thoroughly soaked by watering until you can see water drain from the bottom. You will also want to gently water from the top to prevent the soil from washing out or creating deep holes from pouring water. Be sure you don’t leave standing water in the tray after it drains, as this can cause root rot, and create an environment for fungus gnats to thrive in.
If you run into a situation in which you let your soil dry out too much and it has become hydrophobic (won’t absorb water anymore), do not panic, it can be fixed! I have found the easiest fix for this is to add a very small amount of dish soap (a small drop is plenty) to your water, make sure it is mixed up in the water, and then simply water your plant. This works because the dish soap will break the surface tension just enough to allow the water to wick through the soil again without hurting the plant.
Depending on how dry your soil got, you may need to submerge the entire container in a bucket of water with dish soap to saturate the soil.
If you planted more than one seed in your container, there’s a good chance you have several seedlings growing in one container. After about a week or two when your seedlings are about an inch tall or so, you should thin out the seedlings and leave only the best one. Contrary to what you may think, the best seedling is NOT the tallest one! You will want to choose the shortest seedling that has good leaf development and looks healthy.
To thin your seedlings you can either use a pair of scissors or kitchen shears and snip each stem flush with the surface of the soil, or you can carefully pull the seedling out if it’s still small enough. It is generally recommended that you try to pull the seedling instead of cutting it, however, you will want to cut the seedling if it has true leaves, as the roots are much more developed at this point.
Using scissors to thin pepper seedlings
If you are growing your seedlings in a regular potting mix, this is usually not an issue, and you will most likely not need to add any fertilizer to your plants, as most potting mixes contain a sufficient amount of nutrients.
Fertilizers become more important when you are growing your seedlings in peat moss or a soil-less mix that does not contain any available nutrients. If this is the case, you will want to add a small amount of fertilizer once your plants have their second set of true leaves (do not mistake cotyledons for leaves!).
When applying fertilizer at an early stage, be sure to use a very small amount, roughly 1/4 of the recommended use – you may also want to try it on one isolated plant first before applying it to all of your plants. You will not need to add fertilizer every time you water, in most cases every ten days or so should be fine – be sure you adjust the amount you add as your seedlings get bigger – just don’t overdo it.
Using hydroponic nutrients as a nutrient supplement to potted plants
I like to use a liquid fertilizer for my seedlings, as it is easy to measure the right amounts, and it can be easily mixed in to a jug of water. If you have liquid hydroponic nutrients, most of these can be used for soil as well, just be sure to check the label or website to make sure, and to find the proper amounts to use for soil application.
When to Re-pot Plants
In almost all cases you will inevitably need to re-pot your plants to larger containers. Depending on what size container you started out with, this could be fairly soon after your seedlings emerge, or it could be up to a month after.
If you started your seeds in a 72 cell flat, you will need to re-pot your seedlings around the time they have a solid set of first leaves. If you planted in 2 1/2″ to 3″ containers, you should be able to wait a good while longer before needing to re-pot – somewhere around three to four weeks after your seedlings have emerged. Of course you will have to use your own judgment in some cases, for example, certain herbs can still be very small after a month, and may not need to be re-potted yet.
A variety of container sizes. Transplant plants in cells (left) to larger pots like the one on the right
Re-potting plants is not hard, you just have to be careful not to damage the roots too much in the process. Before you remove your seedling from its container, first prepare the new container by filling it about 1/3 to 1/2 full of new soil. Once you have done this, start by watering the seedling in its original container to help hold the soil together and prevent it from crumbling apart.
After a few minutes when the soil has absorbed all the water, gently squeeze the sides to help loosen things up. You may need to use something flat like a popsicle stick to run around the edges of the container, and a spoon to help hold things together. Be careful not to hold or pull the seedling out by its stem, as this can damage it!
Once you have the seedling out of its original container, carefully place it in the center of the new container, and then fill around it enough to hold it in place. Continue filling and gently compacting the new soil around the seedling until the container is filled. For most seedlings you can add more soil and cover the stem to just below the first leaves – Roots will eventually grow out from the stem and encourage healthier growth. Be sure to verify that this can be done with your particular plant type before trying though.
If you have followed all of the steps in this guide, you are well on your way to have healthy plant starts that will soon be ready for planting outdoors. When it does come time to plant your starts outside, remember that you must always harden off plants that were started indoors. This is a simple process that involves taking your plants outside for a bit of time each day for a week before planting. It is recommended to start out at an hour or two the first day, and then simply add an hour each day after. You will also want to put your plants in a shaded spot for the first day or two.
If you have any questions or comments, please leave a message in the comments section below.