Seed Sowing Tips for Australian Gardeners

I’ll admit it. After over 20 years growing plants commercially, I still look at seeds and think: “How will you ever turn into a plant?” Then they do what seeds do, which is to grow, and I’m thrilled to bits! The magic never dies. Try these general seed sowing tips to boost your gardening success-rate. It’s easy!

“General” Means “General”

First, a little disclaimer. Whether we’re talking about plants or people, it’s easy to make generalisations. That doesn’t mean they’re always true. For example, we cover most seeds with soil after sowing, but some seeds like to get some sunshine before they’ll germinate. A lot of varieties in the sage family of plants have this unusual trick, and sowing them literally means scattering the seeds on top of a hospitable growing medium (no soil covering) and keeping them damp.

Luckily, most plants stick to the rules we’re about to share, but we do recommend looking up sowing tips for individual plant types if you have the time.

Seedling Medium and Seed Beds

Open Ground Sowing

Before we get down to sowing seeds, we need to think about the soil environment. When sowing in open ground, the first step is definitely working in a little compost. Make sure it’s very well broken down. 

Is Your Compost Good?

You shouldn’t be able to see what went into the compost - and it shouldn’t be generating much heat from inside the heap. When you pick up a handful, it should have a nice, light, crumbly texture. Colour is less important - some folks think it should be black, but that’s a myth. A nice deep-brown is perfect. 

My top tip is to take a handful and smell it! If you’re getting a tannin or ammonia smell, it needs more time.  If you’re getting a nice, earthy smell, you should be good to go. 

Making a Welcoming Place for Finer Seeds

After you’ve worked in your compost, give the bed a week or two to settle, keeping it moist. When it’s time to plant, it pays to pay a little attention to what’s in the planting furrows, especially when you sow finer seeds. You can make the furrows a little deeper than necessary and sieve a thin layer of soil into them. Or you can just pick out any pebbles or chunks of bark. The main thing is to make sure that delicate roots have somewhere to go. 

Sowing in Trays

Making your own seedling mix

A lot of people recommend making your own seedling mix out of coir peat, vermiculite, and perlite mixed equally. It has the advantage of being pathogen free, but I do have a few problems with this mix starting with cost and ending with water management. After all, coir peat and vermiculite both hold a lot of water. That’s offset by the perlite, but it’s still tricky. However, if you’d like to give it a try, feel free. 

Commercial seedling mixes

You can buy commercial seedling mixtures, and I’ve come across all sorts - both good and bad. Some of them are too fine-textured to drain well, so test them by filling a tray and watering it before sowing. 

If water tends to pool on top and takes long to drain away, you have a problem.  You can offset this by mixing part of it with composted bark, lining out the tray with this and putting a layer of the finer mix on top. Test the result by watering it. You want water to drain through quickly. 

Any good potting mix

For most veggie seeds, I choose an ordinary potting mix that I can trust. It usually has some chunky stuff in it, which is good. I can always pick out the coarser bits where the seeds are going to lie. 

For finer seeds, I grab an old baking sieve, and sift a thin layer over the top of the medium, making a nice soft place for my seeds to lie. I scatter my seeds, and use my sieve to cover them, sifting in only enough for the seeds to be covered. I sometimes have to repeat this after the first watering when the soil particles have settled. 

Rule of the Green Thumb No1. Not too Deep

A lot of folks sow seeds too deeply. The seeds do germinate, but the poor little baby plants just don’t have the power to push up through all that soil. They simply run out of energy before seeing the light of day.

As a general rule, use the diameter of the seed as a guideline and cover the seeds to the same depth as their diameter. So, a seed with a 2mm diameter gets 2mm of soil on top.

Need a margin for error? Seeds are more likely to forgive planting too shallow than planting too deep.

Rule 2: Moist But not Constantly Wet

Unless you’re actually growing bog plants, seeds don’t want to grow in a bog. They’ll get sick and die because their emerging roots need oxygen as well as water. In practice, this means watering until the soil is fully saturated when you do water, and then withholding water until the soil’s surface dries out. 

How often this happens depends on environmental factors as well as the type of soil you’re working with, so there’s no simple recipe.

On the other side of the coin, you don’t want your soil drying out at seed depth. A germinating seed is quite vulnerable. It doesn’t have much in the way of roots, so if it can’t find what it needs close to the surface, it can die before the shoots emerge.

The best way to get watering just right, is to check your seeds twice a day at first. You will notice that the soil’s surface is darker when damp, and while it’s showing this colour, it isn’t time to water just yet.

Your fingertip is also a good gauge. Moist soil feels like a squeezed out sponge and you’ll wait a little longer before adding more water. Once you get the hang of it, you’ll know how often you need to check and how often you need to water – but remember that your program may need adjusting depending on weather conditions.

Rule 3: Keep the Seed Where You Put it

This is also a watering-related point, but worth considering on its own. If you use water with big droplet sizes or in high volumes, the soil starts washing around, and seeds can even wash away. You’ve very carefully placed your seeds at the right depth and where you want them to grow. Don’t let heavy-handed watering alter that, especially when you’re working with finer seeds.

Choose a watering can, hose tip rose, or sprinkler that lets the water out gently in fine droplets, and keep an eye on things to make sure that excess water isn’t pooling or running about on the soil’s surface.

Handy Tips for Finer Seeds

Sowing Tips

Scattering finer seeds so that they aren’t too close together can be tricky. One way to get them better-spaced is to mix them with some clean sand. I like to do this in the seed packet, and then I either sprinkle them with my fingers, use the packet itself as an applicator, or use an old spice bottle to sprinkle them. 

Watering Fine Seeds

Root crops should always be sown where they are to grow, and bigger seeds don’t give too many issues because of overly rough watering. But smaller seeds from non-root crops, or seeds sown in harsh weather conditions, may benefit from a little help. That means sowing them in containers. That helps you to control what happens to them more easily and get better success because:

• You’re dealing with a smaller space
• You can sow in shade to help with the germination moisture and then move them to sun once they’re up and growing
• You can bottom-water the finest seeds to make sure they stay exactly where you sowed them.

If you sow fine seeds in open ground, water them very gently. You don’t want to see water pooling or washing around on the surface. I use a hosepipe sprayer that I can adjust to emit a very fine spray.

Bottom-Watering Seeds

Wondering what we mean by bottom watering? It’s easy! Simply soak your pots or trays in a container of water – not too deep – the water level should be just a bit below the soil level. Watch them carefully, and remove them from their bottom watering dish as soon as the soil’s surface shows signs of having drunk up the moisture. It’s the gentlest way of watering your babies, and it only takes a few minutes.

Because finer seeds are close to the soil’s surface, they’re more vulnerable to drying out. If you’re short of time, try pulling a clear plastic bag over your sowing container so that the evaporating water condenses and drips back into the container. Remove it when shoots appear. Overly humid conditions can promote fungal diseases that rapidly kill newly-emerged seedlings.

Back to Rule of Green Thumb No 4: Adjust Care Once You Have Germination

Once seeds germinate, they become young plants, and that means that their needs change. They need the right amount of sunlight, air movement, and less water than they did before. 

Light

If you germinated your seeds in containers in a shady place, move them to stronger light. In winter or spring, you can usually go from shade to sun without burning - but if you’re worried, or it’s summertime, you can place them in a spot with mild morning sun and good light through the day to harden off a little first.

Spacing

Spacing also becomes an issue after germination. Seedlings that are too close together are disease-prone. At the same time, you don’t want to disturb them while they are too tiny to handle the shock. As a rule, you will thin or transplant after the first pair to three pairs of true leaves (not counting seed lobes) appear.

However, if you see signs of seedling disease like toppled over seedlings, you can try saving the healthy survivors by transplanting them to a clean medium even when they’re theoretically too young. 

Bare-Root Transplants

If you’re transplanting bare-root seedlings from bulk-sown trays, you will need to give them some shading and more water than you would an undisturbed plant. A week or so of “babying” should be enough. Once they look comfy in their new home, you can gradually begin to reduce watering and increase light.

5th and Final: A Little Extra Feeding for Babies

We all know that babies need a little extra care. Plants are no different. If a seedling doesn’t get adequate nutrition during the first weeks of its life, it will never reach its full potential as an adult.

Once your seeds are up and growing, consider giving them a liquid feed at least once a week – or even every time you water. Liquid feeds are generally mild and safe to use, and if you choose one with a good balance of nutrients, they ensure that your babies don’t go hungry. They’re especially necessary when growing in potting media which are often poor in nutrients. Even if the medium is pre-enriched, nutrients wash out quite quickly, so a little extra feeding is in order.

In open ground, there’s a better chance of most nutrients being present – but sandy soils are bad at hanging onto nutrients, and clay soils can be so good at it that the nutrient ions don’t dissolve into the soil solution just as they should. Once again, a liquid feed (at least once a week) is likely to be beneficial, if not absolutely necessary.

Have We Covered it All?

The answer is a regretful “no.” But we have given you a few tips and tricks to fast-track your seed sowing success. Chances are, you’ll get good germination, but if you’re especially concerned, you can check out the germination requirements for individual plant species online. Remember, there are always a few plants that love to buck the system. Nevertheless, as systems go, this is a good one, and will work for most veg and flower seeds out there. Try it! Let us know how it worked for you!