This is like that project "Reforesting The Sahara" on youtube. Just like this guy, they were working on the concept that as long as you work hard, anything can grow anywhere. That project's video and channel deleted itself last year probably because dumb investors called it a scam. In reality, there are three reasons why plants grow: water, temperature and nutrition.
As it's a desert, there won't be an easy source of water, and planting plants that require a lot of water like mandragora will kill them immediately. In the desert, the water either seeps deep underground or evaporates, leaving nothing on the surface. You need to first make a barrier that makes it harder for evaporation to steal water from the ground. Then again, the appearance of the ground is also weird. This isn't a land that went through draught, this is a land that has always been a desert, but the appearance of the ground looks like the place just went through a draught.
And then there's the temperature. There are ideal temperature, tolerable temperature, and intolerable temperature. Temperate plants will rarely be able to be planted in the desert unless it has a mutation which allows it to reduce the effect of the heat.
Then there's nutrition, which he tried, but was completely wrong. Compost is not trash in the first place. Trash becomes compost, but it's still not trash when you use them. Composts look no different from normal soil, except with bits of plant matter if the composting process is not 100% complete. And a proper compost smells just like dirt.
This manga used to be fun, back when it was all fluffy monster raising. I'm actually surprised that he's shocked that crops won't grow on the desert.