Hello friend, there are many options to prepare our own substrate, you can visit a carpentry shop and collect the remains of sawdust and place them in a large bag with a little soil, more or less like 30% and in addition to this. , you add vegetable remains, you have to keep the material moist, the decomposition process of vegetables and sawdust can be accelerated by adding sardine remains to the material to stimulate the bacteria that will be in charge of the decomposition process of the material. I assure you that in less than 15 days you will have an excellent substrate for your plants, greetings....