Plant Doctor Archive

Trouble sowing brassicas

I'M having trouble raising cabbage and broccoli from seed. I tried to start them off in a small greenhouse, but most of the seedlings keeled over and died. Can you advise me what I'm doing wrong?

IT SOUNDS as if your seedlings are succumbing to damping-off disease, which is caused by fungal disease invading the base of the stems. Generally, it's brought on by potting mix being too wet, especially when other conditions for growth are not ideal, such as poor light or low or very high temperatures.

There are several things you can do. One is to simply raise your cabbages and broccoli seedlings outdoors where you should have good success during all but the coldest months of the year. Prepare the soil by digging it over and raking so there's a layer of fine soil on the surface, or spread a layer of seed raising mix on top of the existing soil. Make shallow grooves with a stick, sprinkle in seeds about 1cm apart, and cover with just a few millimetres of soil or seed raising mix. It's important not to bury them too deeply. Put in a label to mark the spot and water lightly.

If you still want to raise them in the greenhouse here are some tips:

• Use only new or cleaned pots and trays. You can soak them in a solution of 10ml Janola in one litre of water for 30 minutes or so to sterilise them.
• Use fresh seed raising mix. If older than around six months, spread it on the garden and buy a new lot.
• Sow your seeds thinly and only cover with a very fine layer of mix.
• Avoid overwatering. Only water when the surface of the mix is dry to the touch.
• You could drench newly sown seeds and young seedlings occasionally with a solution of a general fungicide like Bravo to prevent infection.
• As soon as seedlings are visible, expose them to as much light and fresh air as possible.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.