Grow medium

As the grow medium we are going to use a mixture of perlite and soil made from coco coir. Perlite is a lightweight volcanic glass with excellent water draining qualities often used to improve soil water drainage and coco coir is made from the external shell of a coconut. While both mediums are inert, meaning they contain no nutrients, it is highly recommended to thoroughly wash both the perlite and the coco soil before using it. Perlite tends to contain cement-like powder/dust and coco soil can have salt buildup in it. We don't want any of these in the grow medium. After washing the coco it needs to be buffered, where potassium and sodium bound to the coco fibers is replaced by calcium and magnesium.
For an overview on preparing and buffering coco coir check out this GrowGuru article.

Word of advice: The following steps are messy, be prepared to cleanup the entire bathroom after this.

Coco coir brick

40 liter / 10 gallon when expanded, for 2 hempy buckets

Amazon.com, Amazon.de

Chunky perlite

15 liter / 4 gallon, for 2 hempy buckets

Amazon.com, Amazon.de

Perlite, coco coir bricks and 2 empty buckets

Washing perlite

Dump 8liter / 2 gallon perlite in a 20 liter / 5 gallon bucket and fill it 3/4 of the way with water, as perlite floats you will end up with a swimming perlite island. Mix it thoroughly and let it sit for 5 minutes, then scoop he floating perlite bits into a second bucket. When you pour out the leftover water notice that fine slush at the bottom of the bucket, this is exactly what we don't want in the grow medium. Depending on the amount of residue in the water repeat this process 2-3 times. When you are done washing the perlite place it in a plastic bag and put it aside.

Floating perlite on top of the water

Giving the perlite a proper mixing

Scooping the washed perlite to a second bucket

The dust that settled at the bottom of the bucket

Washing coconut coir

Coco soil comes in compressed waterless blocks, before proceeding to wash it first you need to dump a block in 15 liter / 4 gallon water and wait 15-20 minutes for the block to start disintegrating. After 20 minutes mix the soil by hand and break up all remaining chunks in it, if needed add more water. Once the coco brick is fully expanded and broken up the bucket should be about 60% full. Now add 20% perlite to the mix ( 4 to 1 ratio) and mix it up thoroughly. This will improve its water draining properties and help with the washing process. At this point the bucket should be 80% full, the remaining space will be taken up by pure perlite placed at the bottom.

Coco coir block in 15 liter / 4 gallon water

After a few minutes the block starts to fall apart

Fully broken up coco coir soil

Place the mix in a bucket that already has the drain hole ready and slowly start running water through it. Ideally you should wash with twice the volume of water as the soil. The water draining through the hole will never be clear, but that is not the goal here, we only want any salt buildup removed from the soil. Once you finish washing the soil move it to a plastic bag and rinse out the buckets. Now you are almost ready preparing the growing medium, the final step will be buffering.

Filling the Hempy buckets

At this point the buckets are ready to be filled with perlite and coco. First add the pure perlite, keep pouring until the drain hole is completely covered.

Hempy buckets ready to be filled

Perlite added to the Hempy bucket until the drain hole is fully covered

Next add the coco-perlite mix and fill your buckets until the soil height is a 3-5cm / 1 1/2 - 2” from the top.

Filling the Hempy bucket with Coco Coir soil + Perlite mix

Hempy buckets ready for the final flush with pH adjusted water

Buffering the grow medium

The final step of preparing the soil is buffering, where it is soaked it calcium and magnesium rich, pH adjusted nutrient solution for a few hours. For the two 20 liter / 5 gallon buckets prepare ~10 liter/2.5 gallon buffering solution by mixing 1 ml/liter CalMag solution and adjust the pH between 5.8 - 6. Plug the drain hole of the Hempy buckets and drench them in the buffering solution. After a few hours the sodium and potassium stored in the coco will get replaced by calcium and magnesium. Now you can drain the buckets and the soil is ready for use.

Starter plugs

Starter plugs help keeping the sensitive roots of seedlings wet. Its best to place the sprouted seeds directly in soaked rockwool starter plugs and once the roots start to develop place the entire starter plug in the coco soil.