Broccoli bolting means edible flowers for salads, food for pollinators, seeds for birds and seeds for next year’s planting!
8.13.20 I was shocked and delighted this morning when a man at a local nursery said they won’t be getting Broccoli/Brassicas until a month from now! He said the days are still too long, they likely will bolt rather than head up! His voice had a certain authority to it, so I believed him ~ not out to make a buck. He’s referring to transplants. My mind immediately went to seeds, but I could get his transplants and still be ahead of the timeframe if I wait a month.
Bolting, aka running to seed, is normal. It happens when your plant nears the end of its season. It is simply your plant putting up a flowering stalk to make seeds for the next generation. We like edible flowers and letting plants naturally reseed themselves. The flowers bring pollinators and hummingbirds, feed the pollinators and pretty up the garden. Birds eat the seeds, late summer food for them. If you have the space, let your plants finish their life, fall and give their seeds to the earth – self sow, replenish your soil.
Do all plants bolt? No.
- Plants that bolt are Beets, Chard, Cilantro, Lettuce, Brassicas – broccoli, kale, cauliflower, arugula.
- Plants that don’t bolt are Solanaceae – tomatoes, pepper, eggplant. Strawberries, squash, onions and garlic, beans and peas.
- Herbs vary. Some say basil, thyme, marjoram, oregano, mint are ok with bolting. Some herbs though become unpalatable, tough and woody instead of having flavorful tender leaves and stems.
Some plants, like Cilantro, bolt a lot more readily than others, so much so that bolt resistant varieties have been developed. Labels will say ‘Slow Bolt,’ No Bolt, Bolt Resistant. Choose these varieties! Brassicas are biennials, two year plants, so unless the weather doesn’t cooperate, they bolt only in their second year. If you want seeds you have to wait. Or if they bolt the first year, you may not get a head, but you will get your seeds early, and you have edible flowers to sprinkle on your salads!
We don’t like bolting when it happens before we get fruits. We don’t like bolting because it stops the regular growth of some plants. For Cilantro that means leaf harvest lessens as the plant makes the bolting stalk. Some plants, like some lettuces, can get tough and bitter.
Benedict Vanheems at Grow Veg explains that ‘bitter’ in detail! ‘The wince-inducing bitter taste that accompanies this bolting is the result of a rapid accumulation of compounds called ‘sesquiterpene lactones’. Never heard of them? Neither had I till I did a bit of investigation. It turns out that plants manufacture these compounds to give themselves better resistance to pests such as burrowing insects and hungry leaf-strippers such as locusts. These clever plants are literally arming themselves against attack so that they can cross the finish line and produce the seeds of the next generation. It’s a really rather remarkable stroke of evolutionary genius.’
What causes premature bolting?
Temperatures
Up and down weather temps stress often causes premature bolting. From cold to hot triggers some cool loving plants to think it is summer and it is time to flower up and be done. Row covers can help keep them cool.
From hot to cold in fall, a Farmer’s point of view: Planting a bit earlier than ideal is better than a little too late. When planted a bit on the early side, the crop may be exposed to more later-summer heat than desired, but since this exposure occurs before head formation (for cabbage, broccoli, and cauliflower), the effect is usually not a problem. Planting too late, however, can result in no crop whatsoever, especially if there is an early fall.
Hot to cold in spring! To biennials, two year plants like Brassicas, onions and carrots, cold snaps make them think they just had winter and it’s time to make seeds! Planting young plants too early you risk exposing them to cold weather, initiating the flowering process. Heat-treated onion sets decreases the flowering process!
Catherine Stewart urges us to: Assess your climate zone, including your microclimate, for periods of prolonged heat. For example, in cooler but still subtropical zones like east coast NSW, there are often many hot days in November associated with the dry spring season, making an early-spring sowing vulnerable to bolting. Sow during autumn and winter instead. Spinach and broccoli will start to bolt after more than a few days at 24ºC (75ºF). Conversely in some very cold climates, you’ll need to delay sowing some of the summer-grown brassica plants like bok choy and mizuna until early summer. Plants like lettuce and Swiss chard if exposed to very cold temperatures early in their growth may have had flowering triggered which will then happen as soon as the weather warms up.
Cabbage plants bolt when they are exposed to low temperatures (35 to 45 degrees F) for extended periods. Cold conditioning may happen if plants are set out too early or if an unseasonable cold spell happens. After the plants have stems as large as a pencil, they are prone to the flowering response in warmer weather. Broccoli is similar. Initial really cold weather when young may make them quickly bolt in warm weather.
Gardeners speak from their own experience: Some plants just don’t do well sown in spring. Many salad Brassicas fall into this category: Chinese cabbage (pak choi), mizuna and rocket (arugula) are good examples which are all best sown in mid to late summer.
BUT! Day Length is the #1 Bolting Trigger!
Besides shutting down when there is extended heat they don’t like, day length is the #1 trigger to bolting. Plants have their own ‘photoperiodism,’ day length trigger time to flower. Check the sunlight hours the plant needs for optimum growth. Don’t plant longer-daylight flowering veggies too late in the spring. The soon shorter day length will start them bolting! Although most veggies grow best in full sun, in a warmer climate many need some shade, especially to protect them from sunlight during the hottest part of the day, usually the afternoon. Plant them among taller-growing crops, or where they’ll be in some shade from about 2pm onwards, or rig up some shade cloth covers over bent PVC pipe. Paraphrased from Catherine Stewart
Michigan State U says it’s complex interactions between temperature, daylength and stresses of various kinds. Among these, periods of cool temperatures during early growth, followed by long daylight hours are often the most important determinant of unwanted bolting in vegetables. The vernalization process is an important component. They give details of the general process and specifics for Amaranths – beets, chard, spinach, Brassicas – our big winter crops & radish, Umbellifers – carrots, celery, Alliums – onions and Asters – Artichoke & Lettuce.
More Prevention Tips!
Planting Skills!
Choose seeds from plants that are successfully grown in local conditions. Go to your neighbor, feed stores, local farms, farmer markets, seed swaps!
Johnny’s Seeds reminds us some varieties perform better in different seasons, so it is sometimes better — especially for Broccoli and cauliflower — to grow multiple varieties in sequence, than to simply repeat the same variety throughout the season. Research it a bit, to fit your preferences and locality, then keep a list for yourself to refer to next time you will be planting. Put your planting time choices on your garden calendar.
In spring, plant varieties that are quick to mature so they are done before the weather gets much warmer. Then, for some plants, wait for cooler fall to plant more rounds.
Start with the best Seed like ‘slow bolting’ seed, or choose the right variety for your locality. Slow bolting seed really means a variety that’s been bred to withstand higher temperatures. This particularly is true of Cilantro, famous for jumping right up with flower stalks early on. One gardener reports ‘‘Bolthardy’ beetroot has certainly never had this run to seed whenever I grew it.’ Love that name, Bolthardy! Umania is a Japanese chard that tolerates heat and cold, is slow bolting.
Succession planting is smart! Who can predict weather?! It can change 24/7. Sow a few plants every two weeks or so to assure that some of them will do well. You will get some early harvests if you are double lucky!
Correct spacing. Many times more is NOT better! Too much competition for water, nutrients and sunlight are not comfy conditions. It’s easy to overplant when seeds are so tiny. Thin to the best spacing, or only plant as many as you really have room for. Allow plenty of breathing room and enough so mature plant leaves don’t touch each other allowing pest and disease spread. Stressors can be pests and diseases (although succumbing to these can also be an indicator of other stressors). The exception to the too close planting rule is, of course, purposely over planting to thin tiny tasties for your salads!
Water and Soil!
Healthy soil loaded with compost/nutrients and with optimum moisture, encourages the quickest growth. We need that to grow plants that need to finish early before heat. For annuals, the key is to not stress the plant. If a cold spell occurs, then some protection will be beneficial, such as covering with horticultural fleece or moving plants still in their pots inside or into a cold frame.
Keep the water up during hotter weather. Moist soil stays cooler and even one hot day with dryish soil can be enough to trigger a flowering cycle in heat-sensitive plants like cauliflower and rocket/arugula.
Mulch heat-sensitive herbs and vegetables. Some plants like coriander/cilantro and broccoli will bolt to seed if their roots get hot. In summer, Brassicas will do better longer with a deep mulch layer to keep those roots cooler and heads forming.
Use the right fertilizer! Some plants you want to flower and then set fruit or seed, others are there for their leaves and stems. If you use fertilizer high in Potassium or Potash (K), meant for a fruiting plant, on your leafy greens, the nutrient mix will encourage them to flower/bolt! Fertilizers made for growing greens, will be high in Nitrogen (N).
Harvest cut and come again plants early and often. If you keep cutting off growth from plants like lettuce, spinach, cabbage and broccoli, it stimulates the plant to replace it and keeps them from maturing properly. It can extend lettuce harvest for up to 10 weeks! YES! Even if you are not a lettuce eater, grow them solely as companion plants for your Brassicas, you can harvest and compost the healthy leaves, trench them into your soil, or feed your worms with them!
As soon as I notice a plant has started to bolt, I harvest it! Some lettuce varieties do NOT turn tough or bitter if they have been kept well watered and you harvest right away. I cut off all the flowering branches of Broccoli and it comes back with more sideshoots! Try it for yourself. Some gardeners like bitter, and it may be good for your health. Frugal gardeners may cook/stir fry anyway and disguise bitter taste with other veggies, sauces and spices.
If your plant bolts, if there is time, replant. If there isn’t time before you would be planting something else, put in some small fast growing edibles to hold space for the next other planting.
Plant at the right time! Only one month before or after can make all the difference!
Praise the Garden Gods & Goddesses for all the beauty and blessings.
Updated 8.28.23
Love your Mother! Plant bird & bee food! Think grey water! Grow organic! Bless you for being such a wonderful Earth Steward!
The Green Bean Connection started as correspondence for the Santa Barbara CA USA Pilgrim Terrace Community Garden. Both remaining Santa Barbara City’s community gardens are very coastal. During late spring/summer we are often in a fog belt/marine layer most years, locally referred to as the May grays, June glooms and August fogusts. Keep that in mind compared to the microclimate where your veggie garden is.
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