A bit over a week ago I planted some spinach seeds, and sadly they didn’t germinate. I began a bit of research as to why. Despite my spinach varieties being hardy to warm weather, they still need cooler soil to germinate! The adult growth stage can handle warmer temperatures but the seedlings are too vulnerable still.
I began to wonder what I could grow with my current temperatures. It’ll also be handy to know the minimum temperatures for when the seasons change.
Whilst my plants aren’t being planted in soil, instead hydroponic is usually planted in rock wool or peat moss, the germination temperature should theoretically remain the same.
| Optimal °F | Optimal °C | |
| Amaranth, Red Leaf | 68-75 | 20-24 |
| Basil, Purple Petra | 65–85 | 18-30 |
| Basil, Genovese | 70 – 90 | 21 – 32 |
| Broccoli | 45 -85 | 7-29 |
| Cilantro | 55-70 | 13-21 |
| Cucumber, Lemon | 70–90 | 21-32 |
| Kale, Nero Toscana | 65–85 | 18-30 |
| Lettuce, Little Gem (Romaine) | 40-75 | 5 – 24 |
| Lettuce, New Red Fire | 60–70 | 16-21 |
| Lettuce, Red Sails | 60–70 | 16-21 |
| Lettuce, Red Salad Bowl | 50-72 | 10-22 |
| Pepper, Cayenne | 65-95 | 18-35 |
| Pepper, Jalapeño | 65-95 | 18-35 |
| Spinach, Matador | 50–75 | 10-24 |
| Spinach, Lavewa | 50–75 | 10-24 |
| Spring Onion | 68-77 | 20-25 |
| Swiss Chard, Bright Lights | 75–90 | 24-32 |
| Swiss Chard, Lyon | 50 – 75 | 10 – 24 |
| Taisai, Pak Choy | 50- 80 | 10 – 27 |
| Tomato, Marmande VR | 60 – 70 | 15 – 20 |
| Tomato (Cherry), Supersweet 100 FT | 75 -90 | 21-32 |
| Tomato, Sam Marzano | 70–90 | 21-32 |
I measured my Aerogarden water and it’s hitting a maximum of 85°F (30°C)! No wonder my spinach never sprouted, its ideal temperature is 50-75°F (10-24°C). Its just way too hot for them.
I’ll have to wait a while for the weather to get a bit cooler before I can sprout spinach; in the meantime I can try growing some Bright Lights Swiss Chard and Nero Toscana Kale.
Bright Lights Swiss Chard, Image Courtesy of Botanical Interests 
Nero Toscana Kale, Image Courtesy of Botanical Interets