Direct sowed plants not growing well
First time gardener. Since it's supposedly easy I chose to use SFG. Read Mel's book. This post is about the tiny growth of 3 of 4 of my plants I direct sowed April 24th. Arugula, spinach and beets appeared to have sprouted after 7-14 days but no movement since the initial poke through. Peas are the only thing that looked like a comparable size to a local nursery. I understand arugula should be ready to be harvested around 40 days and we are certainly nearing that and the leaves are smaller than a pencil eraser. The soil is my attempt at Mel's mix. Differences are that I could not get coarse vermiculite. Only medium and I got free compost from our town pile since stores near me did not sell any compost making it seem real unpromising for me to track down 5 different kinds so I gave up and went with the free. It ended up a bit woody as I believe a lot of what is composted appears to be shrubs and trees. I have my own pile started for more compost but it won't be ready for awhile. Our weather in zone 6 for the latter part of spring has been moderately cool and rainy/sun mixes until the past 7 days really warmed up say mid 70's most days. All in all weather seems like no issue and things have been kept consistently moist so I wonder if it's my soil? I will say I did try fish and seaweed fertilizer about 2 weeks ago as well. Tomato seedlings saw a slight boost but nothing else appeared to. Could I have started the seeds too late in spring? Any thoughts or different organic fertilizer or things to try are appreciated.