inside-the-box thinking

e.g.

technically yes, but would someone understand such a translation?

Mit "Gärtchen" kenne ich das nicht, wohl aber mit "Kirchturm":

Siehe auch: Kirchturmdenken

of course: http://www.google.com/search?client=safari&rl...

"inside-the-box thinking" might be okay, but it has a much broader scope than "Gärtchendenken". You could use it, for instance, if someone has a narrow, unadventurous approach to solving a practical problem, or an internal business problem, or even a mathematical problem, situations where "Gärtchendenken" would not necessarily work. I would probably go for something like "provincialism" or "parochialism"; but ultimately it depends on the context.

Often paraphrased with a negative - He doesn't/can't think out of the box.'

...

Vielen Dank für die Hilfe!

"inside the box thinking" is new to me?!
"petty-mindedness" also possible? - though not exactly the same.

Vielleicht bezieht sich der Ausdruck auf Voltaire. In einem von dessen großen Romanen ("Zadig"?) resigniert der Held nach vielen Schicksalschlägen und meint, man solle sich bescheiden "et cultiver son jardin".