No.
They stood amid lush gardens and were invisible like mushrooms.

This would make more sense to me if they were lush orchards. In English, houses dominate gardens. But a house could be built in a lush orchard. Is that a possibility?

«В густых садах они были как грибы»
В этом случае домики в садах сравниваются с грибами. Просто с грибами. Без привязки к месту, в котором находятся грибы. И ясно, где находятся домики. В садах.
Однозначное выражение мысли

«Они были как грибы в густых садах»
Тут можно представить два варианта. Либо слово ГРИБЫ по смыслу связано с ОНИ (домики). Либо слово ГРИБЫ по смыслу связано с САДАМИ
1. Они были как грибы ... в густых садах
Домики в садах сравниваются с грибами
2. Они были ... как грибы в густых садах
Домики сравниваются с грибами в садах.
...
Я бы выбрал вариант «В густых садах они были как грибы»

right, in orchards)

the small houses were hidden in lush orchards like mushrooms in the grass

The meaning is: the houses were hidden behind the trees of the orchards and hard to catch your eye just like mushrooms in the forest covered with the grass.

Plus: in Russian «как грибы» usually associates with something in plenty.

They were hard to discern like mushrooms in the forest.

Thank you, everyone, the possibility of ORCHARD actually makes it all make sense to me.

like mushrooms in the forest

like mushrooms in the grass/leaves - hard to spot

Thank you)) I chose thicket because mushrooms can be in a forest but out in the open, whereas in a thicket in a forest, they’re harder to spot.

Mushrooms normally don't grow in a thicket, but in open space in the grass (на опушках, полянах), under trees or on stumps
They hide under leaves, that's why they aren't visible from the first glance

https://www.google.com/search?biw=1429&bih=939&sxsrf=ACYBGNSAHetCYWsIaJTC0lxCnqIM0MDBvQ%3A1575739826772&ei=suHrXfrgLqKyggeRr5PYCA&q=mushrooms+growing+in+a+thicket&oq=mushrooms+growing+in+a+thicket&gs_l=psy-ab.3...2308191.5472535..5472818...5.0..0.250.5648.6j40j1......0....1..gws-wiz.......35i302i39j35i39j0i273j0i131j0i67j0j0i131i67j0i10j0i22i30j0i67i70i249j0i333j0i22i10i30.fXXeEIKfTD8&ved=0ahUKEwj6gYiliKTmAhUimeAKHZHXBIsQ4dUDCAo&uact=5

a thicket of grass/nettles isn't just a thicket (a dense group of bushes or trees), if I understand this correctly

A thicket is any place where anything is growing very close together OR overgrowing other smaller growths.

We have mushrooms in the states too and we look for them in thickets.

ок