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How to raise seeds in raising trays

How to raise seeds in raising trays

Posted by Josie Clow on 21st Jul 2023

You don’t need to read any gardening books first. You don’t need any fancy equipment. You just need your seeds (these are the best garden seed catalogs that I order from every year) and a few basic supplies to get started. 

Whether you have a dedicated vegetable bed in your backyard, or a cluster of containers on your patio, it all starts out the same way. You have to plant your seeds, and germinating seeds inside your home (where you have the most control) is the best way to do so, especially for seeds that are hard to start. 

Starting seeds indoors is ideal if you want to get a head start on the season, or if the weather is still too hot or too cold to put anything in the ground.

This simple step-by-step tutorial will take you from seed to seedling with a minimum of fuss. Just the stuff you need to know, and none that you don’t. (But if you’re the really-need-to-know type, I’ve added footnotes at the end to explain why you’re doing what you’re doing.)

How to start seeds indoors: a step-by-step guide 

Step 1: Gather your seed starting supplies. 

  • Seeds 
  • Plant markers 
  • Seed starting mix (homemade or store-bought) 
  • Seed tray with humidity dome (often called a 1020 plant tray or propagation tray) 
  • Spray bottle or squirt bottle filled with water

Step 2: Fill your pots or trays with seed starting mix. 

Dump your seed starting mix into a large tub or bucket, pour in a generous amount of water, and stir it up with your hands or a trowel. 

As the seed starting mix starts to absorb the moisture, add more water as needed. (This will take several minutes, as peat-based seed starting mixes are slow to absorb). You want the mix to be uniformly damp, like wet sand.

Fill your seedling pots with this pre-moistened seed starting mix.

Step 3: Sow your seeds. 

Place two to four seeds on the surface of the seed starting mix, and gently press the seeds down so they’re nestled in nicely. 

If your seeds are very small, like basil or mustard, you can leave them uncovered. 

If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height.

Step 4: Label your newly planted seeds. 

Label each row/section as you go, and as you open each new packet. This will save on any confusion later. 

Trust me, you will never remember what you planted where, as most seedlings look the same at birth. At this early stage, cheap plastic plant markers work very well and stay out of the way, so save your big and beautiful metal plant markers for the garden.

Step 5: Keep your seeds moist and warm. 

Mist your seeds with water and cover with a humidity dome. If your dome has vents, keep them open to help with air circulation during the sprouting period. 

Now, you need to add heat. Since sunlight is not essential at this point, your seed trays can be placed wherever it’s warmest in your house, such as an attic, bathroom, laundry room, or kitchen.

If your seedling pots stay covered in a warm nook, the low humidity will keep your seeds happy until they sprout. High humidity will make them sad. Only spritz the seeds with more water if the mix feels dry to the touch.

Within a couple of days to a couple of weeks, the seeds will germinate. As your seedlings start to emerge, some of them will look like they’re wearing little seed hats. 

Germination (the process of a seed sprouting) is highly variable, so don’t stress if it feels like it’s taking forever to happen. In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds).

Step 6: Give your new seedlings light. 

At this stage, the newly germinated seedlings need light. Remove the humidity dome or plastic wrap, and move the seedlings to the sunniest spot in your house (preferably a south-facing window).

Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get. 

Remember that seedling roots are fairly close to the surface and they’re growing in a small amount of media, so they don’t need a deep soak the way larger plants do. 

I like using spray bottles or squirt bottles, as the gentle streams of water won’t displace seeds or damage seedlings.

Step 7: Moving day! 

Transplant the strongest seedlings when they’re ready. After your seedlings develop their first “true set” of leaves, they are ready to be transplanted.

If more than one seed sprouted, choose the strongest one and pinch or snip off the others. You can even keep all of them, but be careful separating the roots if the seedlings are close together. 

Transplant the seedling into a larger container filled with potting mix. Hold it by the cotyledons (the first leaves that appear) and try not to manhandle the tiny roots.

At this stage, you can lightly drench the potting mix using a diluted solution of compost tea or all-purpose fertilizer. Keep it simple, keep it organic, and don’t obsess too much over the nutrients.

Give the seedling plenty of sunlight each day (at least 12 to 16 hours is optimal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.)

Step 8: Harden off those seedlings. 

To get your seedling prepped for a good life outside, you can start to harden off the seedling11 by moving it outside under diffused light for a few hours and bringing it back inside each night. 

Over the next week, move it from diffused sun to partial sun to full sun, and for longer periods of time, until it’s finally kept outside all night.

Step 9: Transplant your seedlings outdoors. 

After the hardening off period, you can transplant your seedling to its final destination, whether straight into your garden or into a larger container. And then, in a couple of months, you can enjoy the fruits (and veggies) of your loving labour!