Starting seedlings inside is such a great way to get ahead in the garden and save money.
Why bother starting seedlings inside? Well, in a garden center, you might pay $2-$3 for 6 seedlings while a packet of seed for that price can have over 100 seeds.
What you’re really paying for is the time that was spent growing those seeds.
Late winter and early spring are a great time to get ahead start on certain summer plants that take a while to establish themselves. Peppers and eggplants are some that benefit from being started off earlier, indoors.
By sowing them indoors in spring, they’ll be a decent size by the time it’s warm enough to plant them in the garden. Then it won’t be long before they start producing.
Seeds will start off in trays or small pots in a sunny space, and be moved into bigger pots as they grow. This gives the plant’s roots space to expand. Don’t start all your summer seedlings off at once. Staggering the sowing, a few seeds every week will also stagger out your harvests.
Remember, these seedlings won’t be planted in the garden for at least another 8 weeks. If you don’t have enough room to store them, or a glasshouse to move them into, don’t sow too many.
What You’ll Need
Sun / Light
This is so important. As the little seedlings emerge they’ll be searching for light. The light from the sun is what will allow them to produce their food.
A seedling that is lacking sunlight will become tall and leggy as it reaches up to try and find the light. A leggy seedling will be much weaker as its stem will be thinner.
Turn your seedling pots or trays every day or two so a different side is facing the sun. This will stop the seedlings from growing on a lean. They’ll always lean towards the light so turning the trays will even it out.
If lack of sunlight is a problem, you can use artificial light to supplement the sunlight such as blue and red LED grow lights.
There are many types of seed trays you can use homemade or store-bought. A seedling container needs good drainage and is the right size for the seedling.
Re-using plastic seedling pots if you have them already is a good option.
Give them a good wash and spray them with some undiluted vinegar. This will stop any diseases or fungal spores that may be in the old seed containers from contaminating your new batch of seedlings.
Homemade seedling pots can also be a good option. Toilet paper rolls with the bottoms tucked in or origami newspaper cups for example.
Egg cartons I find are too small to grow seedlings in well. Water retention isn’t great with the small amount of soil space, and plant roots don’t have much room to spread.
An advantage of a card or paper biodegradable cup is that it’s easy to transplant them. You can simply pop the entire biodegradable pots in the soil of the bigger container, where they will break down. This is helpful when sowing seeds with a delicate root structure.
A disadvantage is that they often break down too quickly and fall apart when you don’t want them too, especially when they’re wet.
If you’re using homemade paper containers, you’ll need to transplant them into bigger pots or the garden before they break.
Store your seedling pots in a tray to catch any water run-off.
Adding a see-through lid over your seedling trays once you’ve sown the seed can help keep the soil damp and warmer. This will also speed up seed germination.
Seed Raising Medium
This is the term for the seed-raising mix you use.
Choosing a store-bought seed raising mix helps with growing healthy seedlings inside as it’s clean and sterile.
If you want to make your own seed raising mix with homemade compost, it’s definitely an option but you do run the risk of bringing in pests and diseases. You’ll need to add other components in too such as river sand and coconut coir for drainage and water retention.
A good seed raising mix has both good drainage and good water retention and a little fertiliser to feed the seedlings as they grow. They often contain Trichoderma too which is a natural bio fungicide that helps protect your seedlings against diseases.
Seeds don’t need any fertiliser to germinate, only the correct amount of water and the correct temperature.
The seed itself has a food store of nutrients that will last them 1-2 weeks, until their true leaves form. The first set of leaves a seedling form are not considered the true leaves. They are in fact the cotyledon or the leaves of the seed itself.
Once you’ve filled your containers with your seed raising mix, water the mixture well before sowing your seeds, then let it drain.
Wetting the seed raising medium like this means it will be damp all the way through and helps keep the moisture level consistent. You don’t want a sloppy wet mix, just damp enough.
Wetting the seed raising mix first will also compact it down slightly so the seed tray is filled well. Top it up with seed-raising mix if you need to, and then wet it and drain it again before sowing the seeds.
Sow your seeds only as deep as the seed instructions tell you! Sowing seeds too deeply is a big reason why seeds fail to germinate. Each plant will have a different requirement.
In most cases a very light covering is all you need. Basically, just enough to retain a little water so the seeds do not dry out.
Most summer seeds germinate the fastest when the soil is at least 20°C (68°F.) If you’re seed raising environment isn’t getting warm enough (are your seeds not germinating?) it may help investing in a heat pad.
Place your seedling tray on the heat pad and it will warm the soil from the bottom. A heat pad made specifically for propagating plants will provide the right amount of heat. If you’re using a heating pad not specifically for seedlings, take care it doesn’t get too hot and kill the seeds.
As much as you think you'll remember, trust me, you end up forgetting what you planted and where and when.
Labels are essential!
Keep your soil nice and damp as the seedlings grow. If you can, water the soil from the bottom by filling the tray that the seedlings containers are in.
Watering from the bottom will encourage the seedling roots to grow down and reach the water. This will create stronger and longer roots.
Let the seedling tray sit in the water for about half an hour to soak it up. Then pour out the water. You won't need to do this every day, just when you see the soil is starting to dry out.
If you can't water them this way, use a soft spray bottle to mist the seed mix with water. This will wet it without moving the mix too much and disturbing the seed.
Do not let the mix dry out but at the same time, don't waterlog the seed mix. That can cause rot, fungal infections or diseases such as damping off.
As the seedlings grow, depending on when they can be transplanted into the garden, some may need to be re-potted into larger containers first.
If your seedling is outgrowing its container, move it into a bigger container. Choose a container that’s two to three times bigger so you won’t need to re-pot it again. You can fill your new pot with potting mix and compost.
Certain seedlings can be buried deep into the new pot soil, to encourage a stronger stem. Tomatoes, capsicums, chili and eggplant all do better when being replanted deeper than their original soil line. The buried stem will grow new roots.
This isn't good for all seedlings though, such as beans or peas or pumpkins as this can cause their stems to rot.
Once your seedlings grow two sets of true leaves, you can start hardening them off to prepare it for life outside.
While the seedlings are inside, gently brush their leaves with your fingers to simulate a breeze.
Place your seedling continuers outside on a calm day for 3-4 hours so they get used to the direct sunlight and outside temperatures.
Decrease your watering to every second or third day. Slowly increase their exposure to cooler temperatures.
As the ground warms and there is no risk of frost anymore, your hardened plants can be transplanted.
Don't rush this step though, it's not worth the risk of transplanting them too soon only to lose them to a cold snap.
After transplanting your seedlings, water them well with a seaweed tonic to avoid transplant shock.