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G'day Morphet ,
And don't forget that recent building sites can
have a few gardening surprises hidden around the place. One to be careful of
around new foundations/masonry/brickwork etc, is that there can be a lot of
lime /cement splashed around, plus the leaching from the new construction.
This can create a major and often toxic change in the soils pH. You get the
same problem in new concrete pots, but it stabilises after a few months.
Just be careful about rushing in to quickly. As for how close to the
building, I would go out and have a look at few mature citrus trees and
then decide. Do you want to have to prune or shape the tree to keep it
controlled or do want to be able let it do it's own thing. You don't
mention where abouts you are, but generally I would recommend the 'Eureka
Lemon', it's quite an acceptable fruit, a tough variety that is happy in
varied climates and not needing much attention, and best of all, it is one
of the few citrus that gives fruit all year round.

China
Wingham
NSW

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p.s. Professionals built the Titanic,
Amateurs built the Ark!