How to Seed Start and Care for Seedlings is part 2 in the Seed Starting Series. In Part 1 we discussed how to prepare for starting seeds indoors including gathering and preparing supplies, learning about growing zones, and deciding what seeds to start and where to buy them.
In this part of the series we will discuss how to seed start and care for seedlings as well as setting up an indoor seedling station.
Table of Contents:
- Prepare Your Seed Start Supplies
- How to Plant Seeds
- Seed Start Tips
- Seed Start Germination
- Indoor Seed Starting Setup
- What are leggy seedlings?
- Caring for Seedlings
Prepare Your Seed Start Supplies
In the first article of this series we left off with cleaning and sanitizing seed pots and preparing the planting medium. With those things ready it’s time to proceed to planting the seeds.
Set out all your supplies so they are handy.
Read Part 1 of the Seed Starting Series
What you’ll need:
- Prepared Soil
- Pots and Trays
- Seeds
- Plant Tags/Labels – Permanent Marker
- A Spade or Small Shovel
- Dibber – Optional
- Spray Bottle with Fresh Water
It’s helpful to pre-write the labels of each variety you’ll plant and set them with the corresponding seed envelope.
How to Plant Seeds
With your supplies at hand and seed starting mix and pots prepared, we now get to the fun part. Ok, it can be a little tedious, especially if you have a lot of seeds to start. But it’s not hard so, put on some music or an audio book and get planting.
Using a spade fill the pots one at a time with a generous scoop of seed starting mix. Tap the sides and bottom of the pot to settle the soil. You may have to do this a couple of times. Be sure to tap well so there are no large voids in the soil. Scrape any excess soil off the top and very gently press the top of the soil, not to compact it, just to smooth it. Place your filled pots into the trays.
Decide which seeds you’ll start with. Check the packet for the depth at which the seed needs to be planted. If there is not a depth recommendation, plant the seed twice as deep as the seed is wide. So, if the seed is about 1/8” wide, plant it ¼” deep.
Using your finger or a dibber create a divot or hole in the center of the soil. Drop in 2-3 seeds and gently smooth soil over the seed. Spray the soil with water and you’ve done it!
Seed Starting Tips
Here are some handy tips for planting seeds:
- Start at least 2 plants of each variety – This will give you a backup if one doesn’t germinate or dies when transplanted.
- Place 2-3 seeds in each hole – Sometimes you’ll get a bum seed that doesn’t germinate so, doing more than one will give better chances of having at least one seedling. Newer seeds may have a better germination rate and you may be able to get away with just 1-2 seeds. Germination rates declines as seeds age. So, it’s a good practice to plant 2, 3 or even 4 seeds of an older variety to give you better chances at germination.
- Keep track of where you’ve planted – Work methodically so you don’t lose track of where you’ve planted. Sometimes you can’t see seeds once their planted. Surface sown seeds are usually very tiny. You’ll find your rhythm and what method works best for you. A few ways to keep track are:
- Plant single variety at a time labeling as you go.
- Create divots in all the pots of a single tray, covering the seeds as you go so you have a visual cue of where you’ve planted.
- Start with pots out of the trays. Add the pots to the trays one at a time once you’ve sown them.
- Plant seeds and add the label to the pots one at a time to indicate which pots are sown.
- Pre-write the labels – When choosing which seeds to plant, decide how many pots are needed and write labels for each pot. Add the label to the pot right before or after planting the seeds. This can act as another visual cue and help you keep track. If using multiple cell pots, one label may be all that is needed for each container. However, when transplanting to the garden you may want to label each plant.
- Plant in batches – Not all seeds need to be started at the same time. Plan out when seeds need to be planted and set an alert in your calendar. (See the Zones and Growing Seasons section).
- Fill pots to the top – Over time, watering and the weight of the seedling will compress the soil. When planting the seed(s), fill the pot to the top with soil.
- Surface sown seeds – If a seed calls for planting in the surface of the soil. Be sure the soil is moist; this will help the seed “stick” to the soil. Once you’ve placed the seed on top of the soil, very gently press it so it becomes embedded. For these seeds you may underfill the pots slightly.
There you have it! You’ve now planted your first seeds. Congratulations! You are now a gardener.
Seed Start Germination
Next is really the hardest part. The waiting. This can feel like an eternity sometimes. Don’t be surprised if you have the urge to look at your seed pots multiple times a day. It is perfectly normal to stare at the soil willing your seeds to emerge. They will.
Seeds can take anywhere from 3 – 14 days to germinate, sometimes longer. So, what do you do in the meantime? Be sure the soil stays moist by misting the surface with water when you notice the top is mostly dry, about every 1-3 days. Be carful not to overwater. Humidity domes can help keep the soil moist and warm, use them in the germination period if you have them.
Seeds like to be warm and cozy to germinate, some prefer warmer soil than others. This should be on the seed packet, online description, or you can do an internet search for this info. It’s helpful to have a thermometer near your seeds so you can monitor the ambient temperature of the room. Heat mats are also helpful but are an added expense, see the list below for more information. Note that if the temperature of your seed growing space is cooler, your seeds will still germinate, they may just take a little longer.
Indoor Seed Starting Setup
Decide on a dedicated place for seedlings to live. Once your seeds have sprouted, they will require some care and monitoring and having a designated area to house for your seedlings and all your tools is very helpful.
Work with what you have. Don’t feel pressured to go out and buy everything on this list. My first year of seed starting was a hot mess and I had to work with what I had on hand. I was constantly shuffling seedlings to give them adequate light and space when they got tall. The items below are things that can be acquired over time. Just be aware that these are options and if you can make the investment, these tools will make seed starting and care much easier.
Heat Mats and Temperature Controller:
Though not completely necessary heat mats are very helpful in aiding germination, especially if you’re starting seedlings in a cold area like a basement or garage. Seeds have different temperature requirements to germinate depending on the variety and may take longer to sprout in colder temperatures.
Heat mats come in a variety of sizes. Without a temperature controller the mats will maintain a temperature a number of degrees above the ambient temperature, typically about 10˚ F. Check the description of the mats you purchase so you know what to expect.
A thermostat temperature controller can be used to adjust the heat mat temperature and keep it consistent. They include a probe that is inserted into the soil and monitors the temperature. When the heat mat is plugged into the thermostat controller and the probe is in the soil, it will automatically turn the heat mat on and off to maintain a preprogrammed temp.
Grow Lights:
All seedlings need light to grow. Some seeds need light to germinate some do not, do a little research so you know which varieties prefer light for germination. Be sure you provide a light source for ones that need light to germinate or keep these ones close to a window that gets good sun.
Lights are super handy for growing seeds indoors. Without proper light, seedlings can become leggy and weak. Grow lights are a fairly inexpensive supply and a great investment if you plan to grow from seeds for many years.
Look for 5000 Lumen Daylight bulbs. They can be purchased in individual bulbs or in shop light sizes. Note that you may need to have some way to hang them over the seedlings. Zip ties, picture wire, or pulleys work well. I prefer pulleys or link chains with s hooks so the height of the lights above the seedlings can be adjusted as they grow.
When seedings first emerge, suspend the lights 3-4 inches above the rim of the pots. Observe the seedlings, if they get brown edges the lights are too close. Reposition the lights as the seedlings grow keeping them as close to the seedlings as possible without the leaves touching the lights. Monitor the seedlings for signs of overexposure and reposition the lights as needed. Seedlings need about 12-14 hours of consistent light per day. A timer works well to automate when the lights turn on and off.
What are leggy seedlings?
Seedlings become leggy when they are too far from the light sources and are stretching out to get their leaves closer to the light. Leggy seedlings will have weak stems and can fall over. Their overall health can be compromised if allowed to get leggy.
Adjusting the proximity of the light source so it’s closer to the seedlings will keep this from happening. Make sure you have enough lights to cover all the seedlings evenly.
If you are keeping seedlings next a window for light, you may need to rotate the pots or trays regularly to keep the seedlings upright. Monitor them for leaning and rotate as needed.
Another reason seedlings get leggy is from too much heat. Once your seedlings have sprouted either turn down or turn off the heat mats. If your seedling station is in a very cold area try setting the mats to between 63˚ – 68˚ F. If the ambient temperature of the space is between 60˚ – 75˚ F the mats are no longer necessary and can be removed.
Other useful equipment for your seedling station:
- Power strip – If you have lights, heat mats and a fan you will need to have a power strip and access to an outlet.
- Light timer – It can be a nuisance to remember when to turn on and off the lights. A timer automates this process for you, and they are fairly inexpensive. These timers can be used for fans also.
- Shelves – Wire shelves are a great tool for a seedling station and can be very affordable. They also work well to hang lights from.
- Tarp – You may consider putting a tarp or some sort of waterproof material under your seedling station. Not only in case of water spillage but also sometimes soil gets dislodged and ends up where you don’t want it. A tarp can aid in keeping your space clean.
- Indoor greenhouse – I don’t have one of these, I haven’t felt that I needed it. A benefit of having a greenhouse is if you have a particularly cold space or want to expediate the germination process. When used with heat mats or placed over or near a heat register, the greenhouse will keep seedlings warm and cozy. A drawback is airflow. You want to be sure seedlings have plenty of ventilation.
Caring for Seedlings
If you’ve used humidity domes for germination, they can be removed once the seeds have sprouted. It’s good to reduce the barriers between the seedlings and light and air.
It’s also good to reduce heat on the heat mat. An adequate temperature for seedlings is around 65 degrees. There are some exceptions, of course, but this is a fine general temperature. If your space is already that temperature consistently you may not need the heat mats anymore at all. It’s also ok for the ambient temperature to be cooler overnight. Take care that the temperature does not fall below 50˚ at night. Turning on the heat mats and/or adding humidity domes overnight in a cold space is a good practice.
Watering Seedlings
A mister or spray bottle are great for keeping soil moist before sprouts emerge. Once the seedlings have broken the surface it is preferable to water from the bottom of the pot. Bottom watering encourages root growth as the roots have to grow down through the soil toward the water source. This activity in the root system also strengthens the seedlings.
Seedling trays are useful for this reason. Water is poured directly into the tray. My favorite trays are from Bootstrap Farmer. They are very sturdy and hold up well over time. Other trays I’ve used are flimsy and can break easily.
Some tips for bottom watering – Remove one pot from the tray and pour water into that void. Fill the tray about ½” inch full. Check the water level after a few hours if there is still water in the tray pour it out or siphon it out with a turkey baster. Be sure the seedlings aren’t sitting in standing water for long periods of time, this can promote disease.
Take care not to over water. Check the soil moisture every couple of days. Even if the top looks dry there may still be plenty of moisture in the soil. Gently probe your finger into the soil if it feels pretty dry about ½” deep it’s time to water.
New small seedlings don’t require too much water. As the seedling get bigger their water requirements will increase. Continue to bottom water until the seedlings are ready to be transplanted to the garden.
Air Flow for Seedlings
Having proper air flow is very important to the health of your seedlings. This helps stave off fungus and disease. Run an oscillating fan in the room near the seedlings, it doesn’t have to blow directly on them. If their little leaves quiver that’s great.
A light breeze also helps to strengthen their stems. As they get bigger and closer to transplantation, the fan could blow on them to help their little stems get ready for life in the outside world.
Thinning Seedlings
Because you’ve planted multiple seeds for each variety it’s important to thin them to a single stalk when they’re big enough. If left bunched together they will compete for nutrients, and you could end up with a bunch of puny plants rather than one strong one.
The exception to this is tomatoes and peppers. I’ll get to that in a minute.
Once the seedlings are about 1 – 1 ½” tall and have their first set of true leaves, they need to be thinned to 1 seedling per pot or cell. Examine the seedlings and decide which looks the hardiest. It may not be the tallest one. It should have rich color with healthy leaves and a sturdy stem. Look for one standing strait.
It’s best to gently trim out the other seedlings with clean scissors. Avoid pulling out the seedlings as this may disturb the root system of the seedling you have chosen to keep. You can discard the trimmed seedlings, add them to compost, or throw them in a salad or smoothy as microgreens.
Potting up Seed Starts
I mentioned tomatoes and peppers can be an exception to thinning. This is because they can be easily separated and repotted. Referred to as “potting up”, this when seedlings are repotted in larger containers and continue to grow indoors until they are ready to be transplanted. This can happen more than once depending on timing and type of plant.
A single 1.5” pot for tomatoes or peppers can be sown with up to 20 seeds. The nice part about this is that you can start all tomatoes or peppers in a single pot which conserves space. Of course, when potted up the seedlings will take up more room.
When the pepper and tomato plants are about 1 ½” – 2” tall and have at least 1 set of true leaves they can be potted up. Turn the pot onto its side and while supporting the plants without pulling on the stems, squeeze the pot to remove the plants. Carefully tease each seedling apart without damaging the roots.
For a boost of nutrients, sprinkle mycorrhizae on the roots during transplant. Mycorrhizae is a symbiotic fungus that is beneficial to plants. Then repot them into larger pots. Bury the roots and stem up to the first set of leaves. This will cause more roots to grow out from the buried stem and make the plant stronger.
The size of pot to move the seedlings to may depend on the variety. Going from a 1.5” pot to a 4” is a logical transition for a first potting up. Transitioning from a 4″ to a 6″ pot would be the next step.
Other seedling varieties can benefit from potting up as well. Anything fast growing that could become root bound should be potted up. Particularly if the seedlings are started in smaller multi-cell pots. Choosing to pot up may depend on timing. If you’ve started your seedlings very early or you’re expecting late season frost, you may need to pot up some of the seedlings. If seedlings are becoming rootbound 2-4 weeks prior to their transplant date, you should consider moving them to larger pots.
Feeding Seedlings
In the previous post in this series we talked about seeds having all the nutrients they need to germinate. Until they produce their first true leaves, they need no additional food.
When seedlings sprout their first leaves after germination they are called cotyledons. These leaves are actually part of the seed embryo and provide food to the seedling until their true leaves emerge. Cotyledons are typically long narrow leaves that don’t resemble the true leaves of a mature plant. These first leaves can turn yellow and fall off while the seedling grows and develops it’s true leaves. This is completely normal.
Once the plant’s true leaves appear the seedlings can be fed with a diluted fertilizer. Mix the fertilizer at about half the recommended amount on the container for the first few feedings. Water the seedling trays with the fertilizer mixture following the procedure in the watering section.
Liquid fertilizers are easily mixed into water and easily absorbed by the plants. Fish, seaweed, and fish/seaweed emulsions are wonderful for plant babies. Take note, the fish emulsions can have a strong smell that is unpleasant for indoors. A seaweed emulsion is much less potent.
How to Treat Fuzzy Mold on Seedling Soil
Occasionally you may notice white fuzzy mold growing on top of your seedling soil. When addressed early this mold will not be a problem. It does indicate a problem is looming if you don’t take action.
There are mixed opinions as to whether or this mold is harmful. It could be an indication that your seedlings are facing damping off which will kill them. There are also opinions that this mold is harmless, which, so far, has been my experience.
Regardless of the cause, it is treatable. This mold occurs due to high humidity and lack of air flow.
Steps to eliminate fuzzy mold:
- If you are using humidity domes, be sure to remove them for a while during the day so the plants have some airflow. You can put the domes back on at night.
- Spray a peroxide solution on the soil surface. This worked really well for me. Mix 1 tsp peroxide into 1 cup water and add it to a spray bottle. Check the soil every couple of days and re-apply until the mold is gone.
- Make a chamomile spray. Steep chamomile tea. Allow the tea to cool. Transfer to a spray bottle and spray the surface of the soil. Chamomile is naturally anti-fungal and can help prevent mold growth and damping off.
- Cut back on the frequency of watering. Allow the surface of the soil to dry out completely before watering again.
- Run a fan near the seedlings. It doesn’t have to blow directly on the plants. Just having circulation in the room will help.
- Lower the heat. If you’re using heat mats, reduce the heat by a few degrees or turn them off completely.
Now that you’ve cared for your plant babies and they’ve grown big and strong, it’s time for them to be moved into the big wide world. In the next article we will discuss hardening off, transplanting the seedlings, and direct sowing seeds.
Read Part 1 of the Seed Starting Series
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