I have followed the instructions on the seed packet:
– 16 hours of light (grow lamp)
– Water when top soil is dry (spray bottle directly on soil)
– Keep room cool (70 deg F)
These are sun king variety broccoli. The soil is a softer seedling mix. Along the right side of the seed tray are buttercrunch lettuce, but I am not worried about them at the moment. Any ideas why they are turning yellow?
by nivix_zixer
1 Comment
Throw away the spray bottle immediately because surface misting is a notorious trap for seedlings. Spraying only wets the very top crust of the soil while the actual root zone down below stays completely dry. Those little taproots are struggling to find consistent moisture which is causing the plants to stress out, stall, and turn yellow. The purple stems you are seeing are a classic sign of phosphorus lockout which happens when roots are too dry or unhappy to pull up what they need from the mix.
You need to bottom water these trays right away. Pour water into the solid bottom tray and let that soft seedling mix wick it up from below until the surface feels evenly damp. Once the soil has taken up what it needs, dump out any leftover standing water so you do not drown them. Bottom watering builds a much stronger root system because it forces the roots to chase the moisture downward instead of staying shallow.
Right now these are just cotyledons running out of their internal seed energy. Once you fix the watering situation and they push out their first set of true leaves, give them a quarter strength dose of liquid fertilizer. Most seed starting mixes have absolutely zero nutrients in them so they will need a little food soon to keep growing. Get that moisture right deep in the plug and they will snap out of it.