I have grown basil in water for two months, and today I filmed the roots and checked that two new cuttings already have roots.

TL;DR

• Basil (a kitchen herb) grows well in water indoors, with no soil.
• A healthy root is white and firm, and it doesn’t smell bad.
• Take new cuttings before the plant wears out.
• A cutting roots in about two weeks if the spot is warm.
• With the cold in Vitoria, basil only does well indoors.

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• 2× SANSI 15 W E27 full-spectrum (~30 W)
• Smart plugs
• pH pen
• EC/TDS meter
• Small clip fan
• DHT22 temperature/humidity sensor

Two months in

I wrote up how to set up a Kratky for basil cuttings in this article, in Spanish. Today, 22 October, I filmed the roots of the hydroponic basil after two months of fully automatic growing.

The automatic part is a Home Assistant automation that turns on the lights and extracts air when the temperature goes above 27 °C.

There are 2 plants in the reservoir. The water isn’t automatic: I top it up myself. And for this project I use ordinary supermarket nutrients.

The video shows well-grown roots.

The roots of my two basil plants after two months in the reservoir.

The roots are white.

What a healthy root looks like

In hydroponic basil, a healthy root is white or cream, firm, with lots of fine rootlets. It smells like clean water.

Warning signs are brown, slimy or rotten-smelling roots. It’s usually water that’s too warm, not enough oxygen, or a reservoir that lets light through.

An opaque reservoir and water below about 22 °C prevent almost all of it.

On my plant, about 30 % of the roots are in the air right now. On a new cutting the level touches the bottom of the cup; on an established plant, the air gap comes with the root.

My system is Kratky: no pump, the plant drinks and the level drops on its own.

This basil grew from cuttings taken from a plant two months ago, and I have had no problems in all that time.

New cuttings to renew the plant

A kitchen basil plant wears out. After a while it tends to bolt and flower, and the leaves lose flavour.

The best move is to take cuttings before that happens. Cut tips of 8-12 cm just below a node, strip the lower leaves and leave 2-3 pairs on top.

Put them in water or in the cup with clay pebbles, with low light at first, until you see roots or a new shoot.

On 22 October I logged two cuttings with new roots in the wardrobe, at 24 °C and 58 % humidity. For rooting, 20-25 °C air is fine. The water, though, should stay below 22 °C.

They came from a basil plant that was dying at the end of summer. They had been in water for two weeks.

Why indoors and not outside

In Vitoria, autumn nights are already cold. Basil suffers below about 10 °C and any frost ruins it.

That’s why it’s best kept inside, where the temperature is steady. Today’s cuttings are in the wardrobe at 24 °C air.

The basil’s light is 10 W and costs me about 2 € a month.

What to watch

Make sure the water doesn’t warm up and the stem isn’t submerged. The wardrobe humidity, 58 % today, is fine for herbs.

For established basil, usual values are pH 5.8-6.2 and EC 1.0-1.6 mS/cm. For rooting, EC 0.4-0.6.

I run EC at 1.3 mS/cm and pH at 6.

Each week I only check the water level.

If the leaves stay limp for several days, it’s almost always warm water or too few roots.

FAQ

How long does a basil cutting take to root? Between 7 and 14 days at 20-25 °C. A new shoot means roots are there.

Can I keep basil in water all winter? Yes, indoors and under a grow light. Outside, the cold ruins it.

How often should I take new cuttings? When the plant starts to bolt. For a kitchen basil, every few weeks.

What if the roots turn brown? Change the water, clean the reservoir and check that light isn’t reaching it and that it stays below 22 °C.