Broccoli likes a kick in the pants via Ammonium Sulfate when they start producing heads. It’s pure Nitrogen which is what you need for big heads. (20-0-0)
It’s a granular/powder and High-Yield makes a good product, which I used to sell and have used myself. :) About $15 for a 4# bag, but it has other uses in the garden.
You can most likely find it at your local Garden Center. It’s good on anything where you want green, vigorous growth, so Kale, Lettuces, Spinach, Cabbages, etc. The Sulfate alters the Ph a bit, which allows the plant to take up the Nitrogen more effectively.
Also - Broccoli likes sunny and cool conditions. Is it getting enough sun? It’s tricky to get a good crop in the Spring if your Zone heats up quickly in the Spring. And, you have to deal with Cabbage Worms! Ugh! I do a Spring crop, but usually start more plants in August for a Fall crop when there are no bug issues and the weather is still sunny, but cooler. (I’m in Zone 5a)
Those white ‘Cabbage Moths’ that flit around in the Spring are the culprits, laying their eggs in our Broccoli. Row covers help so they can’t get to the plants if they are an issue for you.
I’m keeping an eye on the broccolini I planted a few weeks ago. I’ve never worked with it, but love to eat it. There’s a central stalk with the head beginning to show. Do I eventually cut that so that the plant will branch out, or does it do that on its own?
My herbs are all looking rather lovely right now, and I’m enjoying cooking with them. I just run outside and snip. Perfect!
I have some of that here. I'll do that this afternoon.