One.

Agreed. You can plant spinach a couple of inches apart and thin for salads as they grow, but more than one plant as close as you describe means no usable spinach at all.

Thanks.

Zone 9!!! Much too hot for spinach now even in zone 5.

We hicks plant turnips,spinach, mustard in beds & broadcast the seeds.
But if you do not have the space for that, then I would plant one seed every 6 inches & when the other leave touch, remove every other plant to cook up a mesh of greens.
I do this with kale, I use plugs with cabbage,broccoli,cauliflower,collards.

What jolj says. But spinach grows less tall and wide than kale, so I'd sow every few inches, then thin (and eat the thinnings) when they're an inch or so tall.

If you seed early, you may get much less germination, so it makes sense to plant more densely. This spring I planted spinach every inch or so but only about 1 in 10 seeds germinated, because the weather stayed cold and wet for so long. But however close together you plant, you're better off planting just one seed per hole, because they're easier to thin and won't compete while still tiny.

As mentioned, it's the wrong time of year to plant spinach. Instead, you could try chard/beet greens. I prefer to plant beets for the greens, rather than chard, as I am more interested in the leaves than the stem. They are the same species, the chard have just been selected for leaf and stem production, and the beets for root production. Beets grown in the heat of the summer get woody, but if you just want the leaves it doesn't matter. ;-)

I live on a mountain side, so my nights are still in the 50s with occasional 40s, and days in the high 70s/low 80s. Even with an average 24 hour temperature below 70, the spinach still bolts this time of year. I'll plant spinach again in mid-July through mid-August to harvest this fall and winter. For you, think about planting when your night time temps are in the 50s/60s and daytime temps are in the 70s. You can plant a few every week all winter long until probably mid March, and eat spinach from Thanksgiving through April. (Do the same with lettuce, chicories, cabbage-family plants, carrots, beets for root production, winter radishes, etc. These are the classic cool-season garden plants and make a fine winter garden in warm climates.)

Catherine