mixing up a potting soil for fall greens...what to add?

I have a tub full of soil from pots of things that didn't make it over the past year.
It is not my best potting soil, mostly sand and soil, any nutrition is likely lost.
I wanted to give it a boost for starting seeds in my flats that I will later set out in beds.
I know the seeds don't need much food but the plants will stay there for maybe 6 weeks after germinating.

What I have...
a pint or so of food grade kelp granules
wood ashes from the bakery
Sea 90
a few old vit B capsules
soybeans I could grind (is that what soybean meal is?)
coffee grounds if I remember to keep separate and out of the compost.

What I want to plant is chard, kale and collards and arugula and keep them semi shaded until the weather cools.

EDIT to add....soybeans don't sound like an option
https://en.wikipedia.org/wiki/Soybean_meal
other places talk about roasting first and pressing out the oil then grinding...

I vote for all of the above except maybe the soybeans.

thanks Anne!

I tend to just dump a bunch of 'things' in my mixing tub and hope for the best.

The soybeans I thought I could just grind and maybe soak but I have no way to press the oil out first as is done for 'meal'....they are good organic non-gee.em.oh beans I buy for tempeh.

does anyone have experience using kelp granuals as an additive in potting soil?

yeah kelp granules work well in potting mixes, used them in my seed starting mix this year and the seedlings did look notably healthier. wouldn't go heavy on them though, a small handful per tub seems plenty and more just seems wasteful.

thank you Joao!
I have only a pint so in this big tub of soil it shouldn't be too much.

I usually add a handful of Sea 90 to a tub this size also.

The bakery ashes usually have quite a lot of charcoal bits, not biochar but useable.

It's going to cool down later this week with possibility of rainfall. Can you direct sow some of the seeds in ground? I have broadcasted several batches of brassicas seeds since July whenever space opens up. They all germinate and survive as long as I add some lime to increase calcium and pH. Providing shade and water when they are young is crucial too when it's 100F with 30% humidity. So far I see no bolting and they will revive once it gets cooler.

I could direct sow but it's easier for me to keep up with the watering if I use my wooden flats ..they are deep enough to leave plants until time to set out in the ground and hopefully the rains will begin in october?

With the flats I can easily move them to adjust for sun, shade and rain.
...and they will be right out the back door and some on the porch where  won't neglect them accidently.

I did plant turnips and buckwheat in some bare spaces but the only ones that are up are around the plants I've been watering....I did try watering the seeds but I think it needed a twice a day soak to work...once there's a good rain I expect them to sprout still.

BUT...thursday rain looks promising so we go to the feed store tomorrow to see what we can find.....and I have 5# each of organic wheat berries and rye berries to sow when the wet weather really does begin.

I have been adding ashes to the sweet potatoes and probably need to lime the beans again.  I usually put a handful in my potting mix also.

I probably should test ph someday.....

I ended up adding about a cup of kelp granules, a handful of sea 90, a big handful of bakery wood ash and some extra sand to about 15 gallons soil and sand.

Three wooden flats are soaking up some rain water now for collards, kale and arugula.
I'm saving some old B vt tablets to dissolve in water for when I water the flats.

Maybe I'll get back to some comfrey brew also.
we'll see.