How to Stop Cilantro from Bolting in a Kratky Setup

If you want to stop cilantro from bolting, it helps to know what bolting is. Bolting is when a cilantro plant stops making leaves and sends up a tall flowering stalk instead. Once that starts, the leaves turn thin and feathery, the flavor changes, and the harvest is nearly over.

Why cilantro bolts

Cilantro is a cool-season herb. Warm temperatures and very long days push it to flower and set seed, which is its way of finishing its life cycle. Stress does the same thing: a plant that dries out, is crowded, or is repeatedly shocked by temperature swings is more likely to bolt early.

A Kratky setup removes some of that stress. There is no soil to dry out, and the roots sit in a nutrient solution all the time. It does not remove the effect of heat and light, so those are the first things to manage.

Habits that delay bolting

• Keep the plants cool. Avoid a spot that gets hot afternoon sun through glass, or sits right beside a warm appliance or grow light.
• Harvest regularly. The step-by-step Kratky method guide for cilantro says regular harvesting encourages bushier growth and prevents the plant from bolting too soon. Aim for every week or two.
• Do not run lights around the clock. Plants need a dark period, and very long days encourage flowering. Follow the instructions that come with your grow light.
• Keep conditions steady. Check the water level, keep the roots in the solution, and keep the pH between 6.0 and 6.8, as the guide recommends.
• Do not crowd the container. Give each plant room, so they are not competing for light and nutrients.

Choose slow-bolting varieties

Some cilantro varieties are bred to bolt later than others. Our page on cilantro varieties describes Leisure Cilantro as slow-bolting and Slow Bolt Cilantro as more resistant to bolting, with a longer harvest period. If bolting keeps ending your harvests early, start there.

Plant a little at a time

Even with good habits, a cilantro plant does not last forever. Many growers start a new container every few weeks, so there is always a young plant ready as an older one slows down. Kratky containers need no pump or electricity, so a second jar costs very little effort.

What to do when it has already bolted

Cut the remaining leaves and use them, because they will not get better. You can also let the flowers develop. They turn into the seeds known as coriander, which you can dry and use in cooking. Our post on cilantro vs coriander explains how the two relate. Then start a fresh container from seed, as described in how to grow cilantro from seed hydroponically.

Signs that bolting is close

Watch the center of the plant. Leaves near the top start to look finer and more feathery than the lower ones, the stems stretch upward, and a flower bud appears at the tip. Catching this early gives you a few more days to harvest while the leaves still taste good. Pinching off a young flower stalk can delay the process a little, but it will not stop it for long.

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