Q&A - Seeds

Seed manager Evette Jungwirth answers your questions about growing from seed successfully

Bethany asks “I struggle with carrots. I've tried adding sand to the soil. I don't know if there is anything else I should be doing?”

Carrots can be frustrating because they do germinate more erratically than other seeds and can take 3-4 weeks to germinate. They are best sown when the soil starts to warm up in spring and can be sown right through summer.

It is a good idea to mix them with sand or some sieved garden soil, and try mixing them with radish seed.

Radishes germinate very quickly so you will know where the carrot seed has been sown. Also carrot seed doesn't have a long shelf life so try and buy fresh seed.

Nathan says “I'd like to know a bit about which soils to use for seed raising. I've tried the typical seed raising mix with mixed results, but have had more success with soil and compost from the garden.”

We generally use seed raising mix because it has excellent drainage and a very low nutrient content. This is imperative for raising seedlings successfully as the fine roots can easily be burnt from high salt levels if nutrient levels are too high.

The drainage must be good otherwise the air pockets in the media can compact, effectively drowning the seedlings. But it sounds like you have the formula right with your soil-compost mix so I would suggest keep going with it!

Des asks “Should you sow only one seed per small cell or can you sow multiple just in case some don't sprout up?”

It depends on the size of the seed as to how many you sow per punnet or cell. For something larger like peas, beans or nasturtiums it is best to sow them just one seed per cell (although it is important to note that we always sow seeds like these directly into the ground).

But for smaller seeds this is difficult to do. Sow a few seeds per cell and then you can thin them out at planting time. Alternatively, you can use a seed sower to sow one seed per cell.

Cheryl and Pauline ask about “... the use of smoke water or smoke discs for the sowing of native seeds and when it is necessary. How can we make smoke water and what seeds need it?”

Lots of our native seeds need smoking, and some need smoking and heat to trigger germination.

You can buy smoke water from good native seed suppliers here in Australia. But you can try to make your own by either bubbling smoke through the water using a bee smoker or some other device — or you can collect cigarette butts and put them in a bottle of water, let it brew for a few weeks and then use this horrible smelly stuff to water in your seeds. Disgusting but effective!

Melinda says “My problem isn't so much getting the vegie seeds to sprout, it's getting them to grow. They seem to stop at a certain point but they are too small to move into another tray. I'd like more info on that and whether to feed when so tiny.”

This is a common problem so you are not alone! The main reasons for seedlings failing to grow are lack of light and nutrient.

There are very low nutrient levels in seed raising mixes so once the seedlings have their second set of adult leaves you need to carefully transplant them into a medium with a higher nutrient content.

Alternatively you can start feeding with a very weak liquid fertiliser. You also need to move them into a higher light environment so they can photosynthesise to their full potential.

Some native seeds have special requirements for germination

Molly asks “I have trouble getting capsicums, chillies and tomatoes to germinate. I figure the soil temp isn't warm enough?”

Members of the Solanaceae family do need very warm soil temperatures — up around 25-30°C to get good germination rates. They will germinate at temperatures above 15 degrees but it will take much longer, up to 6 weeks. Whereas seeds sown at 25+ degrees should germinate in 7-14 days.

Mardi says “I get good germination but the seedlings always grow too tall and "leggy" and topple over. I'd like to know about light and it's effect on seedlings please.”

The effect you are seeing is known as etiolation and is a result of the seedlings not receiving enough light, therefore they grow long and straggly as you describe.

You need to harden these plants off over a period of 10-14 days and gradually build up the amount of light they are exposed to.

Jill asks “On seed soaking, how long should you soak for? Small seeds an hour, larger seeds overnight?”

You generally soak all seeds for about 24 hours. Pop the seeds into a container, cover them with boiled water and then leave to soak overnight. This is long enough to break down most hard seed coats. Make sure you plant the seeds straight after soaking otherwise they may dry out and will no longer germinate after that.

In the case of really hard seeds, like Moonflower, repeat the process daily until the seed coat splits and then plant in pots or jiffies.

Nola says “I had trouble with lupins. All but one rotted as they were left to get wet, then I lost the last one.”

Lupins do have a hard seed coat so would benefit from scarifying before sowing. This means you nick the seed coat with a knife or scratch it with sand paper to allow the water to enter the seed more easily. If hard coated seeds are left to sit in cold wet soils for too long they do have a higher chance of rotting.

We generally sow lupin seed in late autumn or mid-spring when the soil temperature is still reasonably warm at around 15-20°C. The seeds can still take 3-4 weeks to germinate so make sure the soil is well drained. If you are sowing in pots, transplant to the garden with care as lupins have a long tap root that can easily be damaged during transplanting.

Rhonda asks “Any tips on sowing winter seedling crops while the summer heat is still high?”

Most seeds will germinate well in warm soil temperatures so the issue is not around germination but more about the plant's exposure to cold and fruit or flower initiation. Cool climate crops generally have a vernalisation period and this is the time they need to be exposed to cold temperatures. Crops such as brassicas have a high vernalisation period but, that said, we still plant our brussels sprouts in late summer so the seedlings get to a decent size and then are exposed to a whole winter of cool temperatures.

For perennial crops such as Echinacea or Comfrey you can place the seeds in an air tight container in the fridge for 4-6 weeks before planting. You then plant the seeds into a soil temperature of 20°C. By doing this you are mimicking nature and tricking the seeds into thinking they have been through a long cold winter and come into spring so it is time to germinate!

Miriam says “I struggle to get the really small flower and herb seeds to germinate. Any advice on tiny seed germination would be greatly appreciated.”

Small seeds can be tricky simply because they are so tiny. Often the reasons they don’t germinate are as simple as the fact that, due to their small size, they get blasted out of the containers by water from the hose or watering can. So try using a fine mist to water them in or water them from the bottom using a capillary type system.

Small seeds can also be buried too heavily under potting media, so try sieving a very fine layer over the top of the seeds. Some fine seeds such as lettuce, alyssum and poppies need light to germinate so don’t need covering at all.

If you want to sow fine seed directly into the garden then we recommend mixing the seed with some sand or sieved soil and scattering the seed/soil mix directly onto the garden. That way you are guaranteed of seed/soil contact and it will stop your seeds blowing away in the wind.

Tomato seeds germinate quickly in warm soil (25°C)

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Clive Blazey's thoughts on providing the right balance of plants in your backyard

Q&A - Green Manures

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Q&A - Mulch

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Q&A - Soils

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Soft green succulents for a lush green garden

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Spring Gardening

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Tomato Growing Problems

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Evette Jungwirth

Evette is a passionate backyard gardener and has been a Diggers Botanical Guide. Over the years she has also headed up the Heronswood Garden Shop, plus our plant, seed and bulb departments, giving her a wealth of knowledge to share with members.

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