Robin Gale-Baker, from Sustainable Macleod, discusses plants going to seed. She has also written articles for this website about various growing techniques, mulch, shade cloth, the art of watering, why weed and why wicking beds. Also a number of articles about growing vegetables and growing fruit trees.
In general usage, the phrase ‘going to seed’ means ‘to deteriorate’. It is derived from the natural act of annual and bi-annual plants going to seed at the end of their life. Once a plant has lived out its lifecycle, it tries to perpetuate itself by producing seeds and these fall to the ground or are wind blown or transported underfoot by animals to another location. A certain number of these seeds will germinate, ensuring the plant’s survival.
There is a second reason, however, that plants ‘go to’ or ‘run to’ seed or ‘bolt’ and that is stress.
Stress can be caused by a number of things:
- Lack of moisture in the soil.
- Extreme weather especially hot weather.
- Planting out of season or too early.
- Unsuitable soil.
The rest of this article focuses on the first three inter-related factors above, namely lack of moisture in the soil, hot weather and planting at the wrong time.
Chronic lack of soil moisture will mean that no amount of watering in hot weather will be sufficient to hydrate plants. The soil will have become hydrophobic (water repellent) and the roots of the plants will have been stunted by insufficient water. Already, you will have unhealthy plants. If your soil has been kept moist, and you significantly ‘up’ your watering during extreme heat, your plants should be fine but plants are often under-watered during summer, especially during periods of high temperatures, or they are watered after the heat, when they have already wilted. It is essential that beds are hydrated for a number of days before heat waves and, during heat waves, watered deeply each evening.
The combination of lack of water and of hot weather in general (and hot weather extremes in particular) leads plants to ‘believe’ that they are dying*. They therefore try to reproduce, and ‘bolt’ rather than producing or maintaining an edible part. Hearting vegetables (such as brassicas (cauliflower, cabbage, broccoli) and lettuce) will split, pushing up a flower which will produce seeds. Stem vegetables (including celery, celeriac and kohlrabi) and bulbs (such as onions) will produce hard, woody stems. Root vegetables will transform their juicy roots to a woody ones.
Note that, whilst you can save the seeds produced by a plant when it bolts, there are usually fewer seeds than when that plant flowers at the end of its lifecycle#.
To prevent bolting, prepare your soil well, incorporating compost for water retention, hydrate the soil through generous, deep watering from the time you plant out, shade the plant from the hot sun with a shade structure or a piece of old sheet or fabric draped over the garden bed, or even set up a beach umbrella. If you can keep plants cool, especially their roots, they will continue to grow healthily. Shade also helps prevent the soil drying out.
A further factor that you can control is when you plant your seeds or seedlings. Before the advent of climate changes, Spring (September, October, November) was warm, Summer (December, January, February) was hot and Autumn (March, April, May) was cool. These days, March and April can be very hot so it is worth delaying the planting of autumn crops till late April or early May or later if it is still hot. Have your seedlings ready in pots and, the moment the weather breaks, plant them out. Remember that autumn and winter crops are cool-weather crops so planting them in hot weather is self defeating.
* An exception is leeks, which produce flowers in cold temperatures following high ones. Stems then become woody.
# Brassica seeds are useless because cauliflower, cabbage, broccoli etc cross pollinate and do not produce true seed.