Why are my Zinnia seedlings dying?

Question

It is a seedling of Zinnia elegans Super Yoga. The cotyledons have dried out and I have no idea why.

Potentially relevant information:

• The soil media is an equal mix of compost, river silt and coco coir.
• I planted around 12 seeds of which only two germinated. The other one also died a day back, although its stem had wilted when I found it.
• They were planted outdoors, in clear plastic cups with a finger sized hole at the bottom.
• They were watered at least once a day in the morning, I checked in the afternoon and added water to any whose soil color seemed to have changed due to drying. I'd say the amount of water given to each was around a teaspoon to a tabespoon.
• The soil was still moist when I found it in this state.
• Temperature these days over here is 32°C max to 16°C min.

Its my first time gardening and my intention is to narrow down as much as possible as to what could be the possible reasons for their death? Nutrient deficiency? Over\Under watering? Too much or too little sunlight? Bad seeds?

Answer 1

Zinnias are rather care free and grow without much fuss. There are many factors that could be at play here.

My guess is your growing media. It looks to be heavy and that causes the seedling to essentially suffocate. I'd say to ditch the river silt. Do a 5:1 mix of compost to coco coir. I'd actually recommend perlite instead of coco coir instead if you can find it.

In the past, I've had some seeds fail to germinate in coco coir, but I'm not sure if that's relevant here.

Sow the seeds again, burying them just slightly. Keep the container in a warm, sunny location and water only as necessary to keep the media moist.

Alternatively, direct sowing Zinnias into the Earth is an easier way to grow them.