Bolting refers to the sudden production of flowers in a vegetable plant. This process leads to the formation of seeds, which eventually causes the desired growth of the vegetable to stop.
Essentially, bolting in vegetable plants begins the reproductive process, sometimes called the plant “going to seed.”
In vegetable plants, bolting is a natural and desirable process from the plant’s perspective.
However, bolting is often seen as a problem for gardeners and farmers since it can negatively affect crop quality and yield.
This typically occurs in cool-tolerant vegetables and herbs that thrive in colder, such as Brussels sprouts, broccoli, lettuce, collards, and other greens.
Causes of Bolting
Temperature Changes
One of the main causes of vegetable plants bolting is drastic fluctuations in temperature. For most plants, bolting is triggered when the plant is exposed to hot weather conditions.
This sudden rise in temperature causes the plants to shift their growth from leaf-based to flower and seed-based in an effort to reproduce before the adverse conditions damage their chances of survival.
Daylight Hours Variation
The length of daylight hours can also play a critical role in vegetable plants’ bolting. When the days become longer during the spring and summer months, plants sense the change and prepare for seed production in response to the increased sunlight.
Cool-season crops, such as Brussels sprouts, broccoli, lettuce, collards, and other greens, are particularly susceptible to bolting under longer daylight hours.
Water Stress
Water stress can lead to bolting in vegetable plants. Insufficient or inconsistent watering can lead to plants bolting as they perceive limited resources and prioritize seed production over vegetative growth.
When we have a particularly dry spring, which we are having right now here in the north-west, then it is important to keep plants well watered.
Onions grown from sets are one plant that is particularly susceptible to water-related bolting and has definitely been a big problem for many people this year.
This deserves a whole article of its own, but onions grown from sets are particularly prone to bolting, so if this is an issue for you, try seeds next year.
Nutrient Imbalances
Lastly, bolting can be triggered by nutrient imbalances in the soil. Excess nitrogen can accelerate plant growth and make them more sensitive to bolting.
On the other hand, a lack of essential nutrients may also cause plants to bolt, as they struggle to grow and reproduce effectively.
Having good healthy, well-balanced soil is the best way of preventing this. Garden in an organic way and add lots of organic matter to your soil every year.
How to Prevent Bolting
Proper Planting Time
One of the biggest causes of bolting is simply plants being grown at the incorrect times. Many cold-loving plants will bolt when grown at the height of summer. Its that simple.
For cool-season crops like lettuce and spinach, plant them early in the spring or later in the autumn to avoid high temperatures that can trigger bolting.
Maintaining Optimal Growing Conditions
Stressful conditions often cause plants to bolt, so it is critical to maintain optimal growing conditions throughout the season.
- Consistent watering: Ensure plants receive consistent and adequate water levels, especially during the hotter months, to prevent bolting due to water stress.
- Proper fertilisation: Over-fertilisation, particularly with nitrogen, can lead to bolting. Apply a balanced fertiliser based on your soil needs and the nutritional requirements of your vegetables.
- Shade: Provide shade for cool-season plants during the midday sun, or grow them in partially shaded areas, to keep them from experiencing heat stress.
Harvesting Techniques
Proper harvesting techniques can also minimise the chances of bolting in your vegetable garden. Regularly harvest the outer leaves for leafy greens, allowing the plant to produce new growth without feeling the need to bolt.
For crops that form heads or bulbs, like cabbage or onions, harvest them when they reach their desired size, as leaving them in the ground too long can cause the plants to bolt.
Harvest root crops like carrots and beetroot before the summer heat to avoid bolting due to rising temperatures.
Bolt Resistant Varieties
Many specially bred varieties of bolt-prone crops are available that are much less likely to bolt.
One common one that comes to mind is “Boltardy”, a beetroot type. As you can guess from the name, this is a bolt-resistant variety.
Many bolt-resistant varieties are available for lots of crops, so if bolting is a regular issue for you, give them a try.
Dealing with Bolting Vegetable Plants
Salvage and Harvest
When vegetable plants bolt, their leaves or roots may become tough and woody, making them less palatable.
However, you can still harvest and consume them if they haven’t reached that point. For instance, bolted lettuce becomes bitter but can be used in small quantities to add flavour to salads.
On the other hand, bolting onions, leeks, and other bulb-forming plants can still be harvested and used before they become overly tough.
Learn and Adjust for Future Planting
To prevent bolting in the future, it’s essential to understand which factors contribute to this issue. Some vegetable crops prone to bolting include cilantro, lettuce, radishes, turnips, and spinach, among others.
Bolting is often triggered by a combination of environmental factors, such as plant maturity, increased daylight hours, and temperature fluctuations.
To avoid bolting in future plantings, consider the following suggestions:
- Choose bolt-resistant varieties: Look for seed packets labelled as slow-bolting or bolt-resistant when selecting seeds for your garden.
- Plant at the appropriate time: Plant cool-weather vegetables as early as possible in spring, giving them time to grow in their preferred temperatures before the summer heat arrives.
- Maintain even moisture levels: Water your plants regularly, ensuring that the soil remains evenly moist to prevent stress that may lead to bolting.
- Use shading techniques: During hot weather, provide shade to cool-season crops using shade cloth or by planting taller crops nearby to shield them from the sun.
- Succession planting: For crops that are sensitive to bolting, plant small amounts at regular intervals to ensure a continuous harvest throughout the growing season.
By observing your vegetable plants’ growth and adjusting your planting methods over time, you can minimise the occurrence of bolting and maximise your garden’s productivity.
Frequently Asked Questions
Why does bolting occur?
Bolting occurs when vegetable plants shift from producing leaves and roots to producing seeds and flowers as part of their reproductive process.
This change happens because the plant wants to reproduce by forming seeds, which conflicts with the gardener’s desire to harvest more tasty leaves or veggies.
Factors contributing to bolting include temperature fluctuations, heat stress, inconsistent watering, and inadequate nutrition.
How to prevent plant bolting?
To prevent bolting in plants, you can:
- Plant at the appropriate time of year, avoiding extreme temperatures.
- Provide adequate shading or relocate potted plants to shady areas during hot spells.
- Ensure consistent watering and proper nutrition.
- Use mulch around your plants to maintain soil moisture levels.
- Choose bolt-resistant varieties when selecting seeds or seedlings.
What triggers cauliflowers to bolt?
Cauliflower bolting is triggered by fluctuating temperatures and exposure to cold temperatures. This prompts the plant to switch into survival mode, resulting in the rapid growth of the central stem and early flowering.
How to handle bolting stems?
When a plant starts bolting, the crop quality declines in terms of flavour and texture. You can still harvest the plant if it isn’t too inedible, tough, or woody.
Once the plant is no longer suitable for consumption, removing and disposing of it is best.
Why do rosette plants bolt?
Rosette plants, such as lettuce, kale, or spinach, bolt as part of their natural reproductive cycle in response to environmental stressors.
Factors contributing to bolting in rosette plants include increased day length, high temperatures, and inconsistent watering.
How to manage carrot bolting?
To manage carrot bolting, try the following methods:
- Plant at the appropriate time of the year, avoiding hot weather and early exposure to warm temperatures.
- Maintain consistent watering to prevent drought-induced stress.
- Use mulch to retain soil moisture and protect carrot roots from temperature fluctuations.
- Thin out carrot seedlings according to recommended guidelines, providing enough space for proper growth and development.