We are coming up to the summer solstice in the southern hemisphere. The days have been lengthening rapidly over the last three months – here in northern NSW, we’ve gained over two and a half hours of daylight every day and further south it would be more. But the days are now nearly at their longest. Between now and the solstice they’ll lengthen only very slightly. Then over the next 6 weeks they’ll ll very slowly shorten again. Over the next three months we’ll gain twenty minutes then lose them again.
It’s really a very noticeable change if you are in the mood for noticing it. Our ancestors did – all the traditional festivals in most cultures (Easter, Halloween, Groundhog day, Christmas, Mayday) are held on these day length marker points , and plants most definitely notice. Most garden crops are highly sensitive to this cycle of lengthening and shortening days. Plants that evolved in the tropics are less sensitive, but crops that evolved in temperate parts of the world got frosted if they got it wrong. The ones that survived were the ones that could discern, reliably, whether the year was heading towards winter, and the best survival strategy was to hunker down, or whether it was heading to summer, and there was time to bring up a new generation.
Humans have had a say in it over the last few thousand years, breeding varieties that are “slow bolt” and turning bi-ennials into annuals and vice versa. But a few thousand years isn’t long in the scheme of things. Generally, lengthening days signal plants to set seeds, and if you don’t want them to (parsley, celery, lettuce, silver beet, chinese cabbage, broccoli…) you’re going to be fighting them. Shortening days signal plants to heart up and store food (onions, cabbages, celeriac…) and if you plant them at the right time they co-operate beautifully.
So, if for the last few months it’s been an uphill battle to get leafy greens, you can blame photoperiodism. The little lucullus (Italian chard) in the picture came up from self-sown seed, and I left it although I knew it would just bolt at the first opportunity, and it has. From now on, it gets easier! Kind of. For the next few months, there’s aphids and grasshoppers and cabbage moths and sunburn weather challenges, and not much room in a garden full of rampant cucumbers and zucchini, but at least the urge to bolt to seed will be more manageable.
So this time I’m planting lettuces, radicchio, parsley, coriander, basil, rocket, aragula, amaranth, and Warrigal greens. I’ll wait a bit longer for the silver beet – the grasshoppers like it too much, and the brassicas – the white cabbage moths like them too much.
On the plus side, I’m harvesting my coriander, mustard, dill, and celery seed now to store for the year.