A swamp? You can't use sprinklers, but the ground stays wet for an extra day after rain.
How would a desert farm play?
My idea for a Desert Farm is it's pretty big like the Beach Farm with various small Oases scattered about. You can farm near these oases with Sprinklers (the oasis is the water source) with an 8 to 10 tile range from the oasis but farther away from these you can't put any Sprinklers. You can still farm those other places watering manually like on the Beach. You should get random item spawns like the Beach and Forest Farms, but matching the Calico Desert's spawn table. There will be various rocky parts functioning like grassy parts on other Farm maps, preventing Farming but walkable and adding needed texture to the map.
Initial trees are all Coconut Palms to match Calico and there should be inaccessible Cactus there around the landscaped edges. And some animal skeletons! This should require some seeding mechanism change for Coconut Palms by making the Coconut the seed, though that makes the Coconut an inordinately valuable Tree Seed compared to the others so it should get some kind of buff when planting. Maybe that Coconut Palms always grow in 4 days without Fertilizer or something similar.
Or!
There is a small river cutting though one corner of the map and Coconut Palm Seedlings randomly spawn within 5 tiles of the river! You could chop them and receive the sapling to replant where you like and it would then grow like other non-Fruit Trees (regular fertilizer mechanics apply). New Coconut Palm Saplings would generate and plant themselves near mature Trees like seeds do for other trees, just skipping the seed stage. That would be fun and no need to change the Coconut at all!
You can Fish the oases but only get Sandfish and Algae. No option for Scorpion Carp until you unlock Calico Desert and even then, the odds are low.
Seeing as the more arid places on the general Stardew Maps all have challenge Caves, I think the Desert Farm should have one as well though I'm still considering how to match the mechanics to the rest of the game. It could be as simple as a small Cave with a Mining bed like 4 Corners and Hilltop, but adding the monster spawns from the Wilderness Farm except they're
always there, unlike the Wilderness Map's nighttime-only spawns. Makes sense, it's dark and underground! Still wondering whether it should work as a simple single level or maybe a 10- or 20- level map with no elevator, each being a randomized map taken from the upper Mines spawn options. Nothing too OP but a source of stone and ores, maybe some artifacts with rare Artifact node spawns? It would be located on the far end of the Farm and not sure if:
• Open immediately but you need a Copper Pickaxe to progress beyond Level 10 because blocked by a big rock
• Remains completely blocked until you upgrade to a Copper Pickaxe
• Remains blocked until Joja opens the regular Mines as it also destabilizes your blocked Farm Mine entrance
Anyhow this seems like a fun mix of opportunities, limitations, challenges and gameplay.