How to Propagate Tomato Seeds From Scratch in Australia

There's a very specific kind of joy in wandering out to the garden, picking a tomato straight off the vine and eating it right there, still warm from the sun. No washing, no waiting, no small talk with a checkout operator. Just you and the tomato.

Getting to that point from a single seed takes a bit more than luck, though. Tomatoes are fussy things — susceptible to fungal disease, magnets for pests, and not shy about sulking if you get the basics wrong. The good news is the basics aren't complicated. Get them right and you'll go from one packet of seeds to more tomatoes than you know what to do with.

Here's exactly how to propagate tomato seeds at home, from seed to seedling to soil.

Choosing your tomato seed

Full disclosure — we're a little biased toward the seeds in our own Tomato Bundle, organic and non-GMO, because we picked the varieties ourselves and we're fairly obsessed with them. But you've got options.

If you'd rather start with a tomato from the shops, go for one that's organic and non-hybrid where you can. Scoop the seeds out, squish them into a paper towel, and pat them dry. That's it — you now have viable tomato seed, no packet required.

How to propagate tomato seeds indoors

Grab a seed tray and use your fingertip to make a small hole, about 5–7mm deep. Drop in two or so seeds per hole and cover them gently and lightly with soil — you're not burying treasure, just tucking them in.

Now for the part that actually matters: warmth and humidity. Tomato seeds love both. A spray bottle is worth keeping close by, since the soil in a shallow tray dries out fast. A translucent plastic tub or glass bowl placed over the tray works well as a makeshift greenhouse, trapping in moisture while still letting light through. They'll want around six hours of sun a day even at this early stage, so don't tuck them away in a dark corner and hope for the best.

From seedling to garden bed

Seedlings usually emerge somewhere between day 7 and day 10. Once you see them, take the greenhouse cover off — they still need direct sun, so don't be shy about giving it to them.

From here the secret sauce is simple: sun and water, consistently, until the seedlings reach about 15cm tall (or 6 inches, for anyone still holding out on the metric system). At that point they're ready for the ground.

When transplanting, handle the roots with care — this is the point where damage happens most often. A biodegradable seed tray makes this step far gentler, since you can plant the whole thing without disturbing the roots at all.

Before you plant, prepare the spot. Tomatoes need at least six hours of sun a day to thrive, so choose accordingly. Dig a hole roughly three-quarters as deep as the seedling is tall, then fill it with water and see how it drains. Quick drainage means you've found a good spot. Water that lingers for a while is often a sign of clay-heavy soil, which isn't ideal for tomatoes.

That watering step does double duty — it also encourages the seedling's roots to grow straight down rather than spreading out shallowly, which sets it up for taller, fuller growth later on.

You'll likely notice tiny white hairs running along the stem. Given the chance, those become roots too, which is exactly why the hole needs to be deep — it gives the plant room to build a proper foundation. Before lightly filling the hole back in, gently pinch off the lower leaves up to the top set. It looks a little brutal. It's not — it's all in service of a stronger plant.

Companions worth inviting to the party

Once your tomatoes are in the ground, it's time to think about who else gets a seat at the table. This is companion planting in action — one of the simplest ways to grow a healthier bed without reaching for a single spray.

Basil is the classic pairing, keeping aphids away from your tomatoes while doing double duty as the star of your next batch of pesto. It's exactly why basil made the cut alongside tomato, parsley and borage in our Tomato Bundle — every plant in there is earning its place, not just filling space.

Beyond that, you'll want to roll out the welcome mat for pollinators. Bees, hoverflies and butterflies are always invited, and the easiest way to get them to RSVP is by planting borage, marigold or a bit of lavender nearby. Each of these has its own uses beyond attracting pollinators — but that's a story for another post.

Grow enough of these together and you're not just growing tomatoes. You're growing a little ecosystem that mostly looks after itself.

Keeping your tomatoes growing strong

Once your plant is settled in, the job shifts from planting to maintaining. Tomatoes are heavy feeders, so a layer of mulch around the base does double duty — it keeps moisture in the soil for longer and slowly feeds the ground as it breaks down. Straw, sugarcane mulch or even dry leaves all work well.

Water deeply and consistently rather than little and often. A quick daily sprinkle only wets the top few centimetres of soil, which trains roots to stay shallow and lazy. A deep soak two or three times a week, depending on your climate, encourages the roots to keep chasing moisture downward instead.

Most varieties will also want staking or a cage once they start putting on real height. Do this early rather than waiting until the plant is sprawling everywhere — wrangling a fully grown tomato vine into a cage after the fact is a genuinely thankless task. As side shoots appear in the joints between the main stem and the branches, pinch a few of them out. This keeps the plant's energy going into fruit rather than a jungle of extra foliage.

Common problems and how to spot them

Even with all this care, tomatoes will occasionally test your patience. Here's what to look out for, and what to do about it.

Aphids cluster on new growth and the undersides of leaves, leaving behind a sticky residue. A firm blast of water usually knocks most of them off, and this is exactly where your basil and borage start earning their keep — they'll draw in ladybirds and hoverflies that treat aphids as a food source.

Whitefly scatter in a small cloud when you disturb the plant. Yellow sticky traps hung nearby help monitor numbers, and a diluted mix of soap and water sprayed directly onto the underside of leaves can bring an infestation back under control.

Blossom end rot shows up as a dark, sunken patch on the bottom of the fruit. It's not a pest or a disease — it's almost always a sign of inconsistent watering, which affects how well the plant can take up calcium. Even, deep watering is the fix here, not a product.

Powdery mildew looks like a dusting of white flour across the leaves. It thrives in still, humid air, so improving airflow around the plant by pruning excess foliage helps prevent it. A milk and water spray, diluted roughly one part milk to nine parts water, is a well-known home remedy that can slow it down once it appears.

Fusarium and verticillium wilt cause leaves to yellow and droop, often starting on one side of the plant. There's no treating these once they take hold — the best defence is prevention, which means rotating where you plant tomatoes each season and choosing resistant varieties where you can.

Catching any of these early makes all the difference, so it's worth a quick look over your plants every few days rather than waiting until something looks obviously wrong.

Harvesting your tomatoes

The wait is almost over. Tomatoes are ready to pick once they've reached full colour for their variety and give slightly when gently squeezed. Resist the urge to judge by size alone — colour and give are far more reliable signs than how big the fruit has gotten.

Twist gently rather than pulling straight off the vine, or use a pair of snips if the stem is being stubborn. Picking regularly actually encourages the plant to keep producing, so don't let ripe fruit linger once it's ready.

If a cooler snap is coming and you've still got green tomatoes on the vine, don't panic. They'll ripen indoors on a sunny windowsill, or you can fry them green and pretend that was the plan all along.

Now go check on your seedlings — or, if you've made it this far, your very own vine of tomatoes. They've missed you.

Get My Tomato Kit