Prepare pots in advance so sprouts can be immediately transplanted once they are ready.
The ideal size pot for planting your seedlings is 4” size. Use 4” pots and not a larger size because a 4” size pot produces a plant with a tight root ball that is easy to transplant later. With a larger sized pot, you’ll get looser, more spread out roots, which are bad because they are prone to getting torn or damaged during transplant. Another benefit of 4″ pots is faster top growth. Small pots constrain plant roots which forces growth upwards. When their roots are allowed to expand their growth outwards a plants top growth is slower.
Pack pots with grow media. On the bottom of the pot, add a 1” layer of hydroton. Hydroton prevents water buildup on the bottom of the pot and creates air pockets so roots get access to air. Fill the rest of the pot with coco coir.
Pre-water the coco coir with distilled water, or tap water pH balanced to 5.8 prior to adding sprouts to the pots.
Planting Sprouts
To plant your sprouts, first make a hole in the coco coir to plant your sprout in. The end of a tube is a good tool for this. The hole should be deep enough that your sprout’s tap root fits all the way inside. Drop your sprout into the hole using your fingertips so its tail is positioned down. If you miss, and the tail isn’t pointing down, it’s usually better to leave it misaligned than keep poking at it and risking damage. The tail will naturally revert itself and point back down on its own as it grows longer.
Gently backfill the indent with the coco coir until your sprout is completely covered. It shouldn’t be buried that deep, no more than 0.25” (0.635 cm) of medium on top.
Water & Nutrients For Seedlings
Water pots using a watering can with a wide distribution and slowly pour until water starts to drain out the bottom of the pot. When it starts to drain out the bottom you’ll know you’ve added enough water. Do not add water past the point it starts draining because an over saturated medium will suffocate sprouts.
Remember the weight of the pot when it is fully watered so later you can pick it up and judge if it needs more water or not by how heavy it feels. As a general guideline, plan to water every 2 days at first, then switch to every day when your seedlings get bigger. Never water past the point it starts to drain out the bottom.
For the initial watering use distilled water, or tap water pH balanced to 5.8. Once seedlings appear and their first two baby leaves begin to yellow, begin adding fertilizer at the following concentration:
Seedling:
350 – 500 TDS
0.7 – 1 EC
During the first week of growth extra phosphorus in fertilizer is beneficial for seedlings.
Adding 2 parts kelp extract / 5 parts humic acid will help enhance root growth.
Excessive chlorine can be harmful to roots. Remove chlorine using vitamin C (ascorbic acid) tablets or a water filter.
Lighting For Seedlings
Add light after your sprouts emerge from the media. Lights for seedlings can be left on 16-24 hours per day.
Seedling:
100 PPFD
5,000 – 7,000 LUX
Delicate seedlings can be damaged by excessive light. Start with low light levels and raise it gradually.
Don’t allow the stems to become elongated and spindly. If you observe any stretching, increasing light intensity fixes this problem.
To encourage rooting, use a full spectrum light with emphasis on blue wavelengths. Red wavelengths are not ideal for seedlings because they promote stem elongation at the expense of root development.
LED or florecent Tube lighting is common for nurseries. The correct type of bulb is often labelled cool white.