How many seeds should you plant?

As many as you can in the space not spent tending to your basal metabolic rate (e.g. 70% of your time to get everyone to agree your team is useful).

This is one of the reasons seeds need to be very cheap.

If they require someone to apply non-discretionary effort in their normal work time, that doesn't count as a seed, because it has a cost.

A seed is "a free thing this person is interested in doing over and beyond their day job."

The question is not "should I have them do something different" (it's their discretionary effort!) it's "should I allow that or not".

You can't redirect that energy, so it's more a freebie that you get to take or leave.

Seeds that don't sprout don't distract the team.

You only invest energy in ones that are growing, which implies that they by construction are viable.

That's the magic of seed planting.