forsythia close to wall

by Marg
(Comox BC)

what kind of root system do they have and how far should they be planted from a concrete block retaining wall?

Doug says they have a basic fibrous root system and you can plant them as close to or as far away from a block wall as your design calls for.

If you're asking do they somehow invade and break up walls - the answer is the same as for any other plant. If the block wall is sound without cracks - then no plant will get in there. If on the other hand, the block wall has cracks and is in very poor condition - then all plants will get in there.

The answer depends on the condition of your block wall. :-)