It is often recommended that large or hard seeds should be ‘chipped’ or soaked before they are sown. The theory is that these seeds have hard seed coats and, by soaking them in tepid water, usually for 12 hours, the seeds will germinate more quickly and evenly when sown. You are likely to see these instructions on packets of lupins, ipomoea, strelitzia, thunbergia, sweet peas and many more. I have usually followed these instructions carefully but recently I have been cheating and not bothering and I am not sure that I have had worse results as a result.

There is one good reason to soak seeds and that is to wash out any inhibitor in the seed coat and this does have an effect. Lapageria is the best known example of this. There may be some of this effect, though perhaps inadvertent, when seeds are sown in the autumn to ‘stratify’ them (expose the seeds to chilling). It may be that winter rains wash away any inhibitor in the seed coat. I don’t know but it makes sense.

But I started to skip the soaking for two main reasons. The first is that not all seeds in a batch will need soaking. With sweet peas the pink and orange shades have much softer seed coats than the blues and it is possible, if you soak them for too long, that they can get too wet and the seeds suffocate. The other reason is that once you have soaked the seeds and drained them, they are really fiddly to handle and are more likely to stick to your fingers than sit on the compost where you want them (these are largely big seeds that you sow individually). If I had unlimited time it would be OK but I usually have lots to sow and transplant and it gets annoying.

So I never soak sweet peas and I  get good germination – I know because I sow one seed per cell in a tray or three for mixed seeds. (more on sweet peas in the next few days)

The other way to help these hard-coated seeds to germinate is to chip the seed coat with a sharp knife or rub the seeds on glasspaper. The latter has never seemed very satisfactory to me because although we are doing this with large seeds I can never hold a sweet pea seed in the right position and rub away a patch of seed coat without taking the skin off my finger tips – it may be a useful technique for crooks who want to remove their fingerprints! So I use a knife to remove a tiny patch of seed coat. If you look at a seed you will see a light or dark patch where the seed was attached to the seed pod (the hilum) and this is where the seedling will grow from so you must avoid damaging this area – scratch the opposite side.

Carefully nick the coat of the seeds

Anyway, I thought I would experiment and I sowed some Ipomoea alba, commonly called the moonflower. I took 12 seeds and I scratched the seed coat of six of them and sowed the others as they were. They we sown on Jan 15 and within a week there were signs of growth. Anyway, by now there are two seedlings up out of the twelve and, you guessed it, there is one of each! They both appeared at the same time.

The one of the left was unscratched and is perfect. The one on the right was a scratched seed and the cotyledons (seed leaves) have some brown marks which I assume is damage caused by the knife. It is too early to make a judgement so far but it sort of confirms that seeds will germinate without extra help. But I will reserve judgement for a few more weeks until another seed pops up.

cotyledons, Germination, germination inhibitor, hilum, ipomoea alba, lapageria, scarify, sowing sweet peas, stratify, strelitzia, sweet peas, thunbergia