I bought a packet of seeds that comes with 250 seeds! There's no way I have the space to plant 250 Silverbeet plants in my backyard, 10 plants maximum. What should I do with the 240 leftover?
Seed lasts quite a while. It is said at least 30 percent of your seed is non viable the next year but I've seen maybe 10 percent or really normal germination. Keep your excess seed in the dark, plenty of room between seeds, lots of air and between 40 and 55 degrees F. If you know your seeds are dry you can vacuum pack them.
In two weeks plant another round. Save the rest in their package. No problem. It is a good thing to have extra seed in storage.
Do you have any seed swap events near you? After making sure I retain enough seeds to get me through an emergency and another years sowing I package them up and take them to a seed swap event.
It depends on how much you like Silverbeet (Swiss Chard). I never liked it much so I let ours go to seed, and it would keep popping up every year from self seeding.
If I wanted to grow some, I'd cast some over some seed raising mix ( sterile media ), and once the cotyledons have appeared, I'd prick out the healthiest to transplant into a 6 inch flat filled with soil compost mix planting in a dense hexagonal pattern. Once they reach 6 inches in height, I'd then transplant the healthiest again to their final destination. When they reach an edible height, I'd strip 20% of the outer leaves to eat leaving the younger leaves to keep growing rather then harvest the whole plant in one go. If you really like the stuff, you could start the whole process again in a few weeks though 10 sounds plenty for a small family. But it might be good insurance to do a second planting in case the first goes wrong with the main issue being that the seeds are planted at the wrong time of the year, and it bolts before you get much produce from it.
You can always keep some of the seed when yours will eventually bolt and use your own seed for planting in subsequent years unless it's a hybrid.
I generally stick leftover seeds in the refrigerator and that seems to work ok. Since Swiss chard is has a fairly low light requirement, so you could use the leftover seeds for microgreens in the winter