Watering clones and seedlings in rockwool

How do I know if the rockwool cube requires watering?

To get watering of rockwool cubes absolutely right, use scales. Weigh a dry cube. Then, saturate a cube and weigh it. Subtract the weight of the dry cube from the wet one. You now know how much water is in the cube when fully saturated (1g=1ml).

Your cube needs water when weight drops to 20-40% of saturated weight. Once you have done this a few times, you will be able to estimate the weight and need for water by feel.

When using this approach with clones, you’ll have to guess the weight of the clone- perhaps 10-25g depending on the size of the cuts. When weighing a cube with a clone, subtract the estimated clone weight and dry cube weight from what is measured to closely estimate water available in the cube.

In most cases, especially when using a seedling warming mat, they will require water once every 24 hours. Cubes should never completely dry out.

Watering the cubes

Immerse the cube halfway into a bucket of pH adjusted (5.0) water for a few seconds. Gently shake out (but don’t squeeze) excess water.

Rooted clones (roots are showing from the cube) should get fully soaked for about 15 seconds, as they have the capacity to uptake water rapidly and will use that quantity in 24 hours. Unrooted clones should just get a little dip; 3-5 seconds. Moist is better than saturated for encouraging root formation.

Do not allow cubes to stand in water. If excess water drains into the tray they sit in, empty it.

Start high nitrogen nutrients when roots have emerged from the bottom of the cube- 1/4 strength for 1st 4-5 days, 1/2-3/4 the next 4-5 days then full tilt thereafter.

This method should give 85-100% success, with roots showing in 5-7 days and profuse root development in 10 days.

Note: a 24 hour rockwool pre-soak in pH 5.0 water before cloning is important