its every plant you try to grow? since you said substrate, this means you're growing in containers?
if both if those questions are yes, i am leaning towards an abiotic problem (not insects or diseases). usually/generally, over watering is the most common problem people new to plant production have. if you're delivering water right to the roots, it really requires very little to grow a healthy plant. if theres not enough air in the substrate pore space (because its overwatered), the root tissue dies, the plant stops taking up water/nutrients efficiently, the dead tissue becomes a disease vector and then the show's over and it looks wilted as fuck... which usually induces people to water more and exacerbate the problem.
container shape / poor drainage can cause these problems too. you really dont want there to be a water level in a container.
as far as references go, the ball seed grower guide is a good reference for container/indoor production for a lot of different plants, mostly ornamentals and flowers.
some of the really good references are crazy expensive though, like APS compedia for disease diagnostics.
for free references online you can trust to be research backed, i would add "cooperative extension" to your searches to look at land grant uni resources made for a public audience. theres one if every state, so even if you're not in the US you can probably find resources (fact sheets, toolkits, reference materials) that are made for a similar climate and distance from the equator.






