Here's a small study done on terrestial plants and compact growth. I have yet to try this myself, but have startet looking for bulbs in the fare red specter. Might be my english messing stuff up for my, but from what I could gather, it's enough to bombarb the plants in far-red for 15 minutts and the end of day???
http://www.clemson.edu/hort/sctop/bsec/bsec-08.htm
http://194.236.255.117/akvarienet/memberfiles/th_of_plantsfile54.pdf
.3 Stem elongation
As described in section 2.2, far-red light reflected by neighbouring plants (or neighbours for short) decreases R:FR in horizontally propagated light, as 'seen' by vertically oriented plant surfaces (see Aphalo and Ballaré, 1995). This happens at low canopy densities, so it is especially important for small seedlings in sparse canopies.
The stems of many plants elongate faster if they receive additional far-red light from the side (see Ballaré, 1999, and references therein). In general, the magnitude of the response to far-red
light depends on the species, developmental stage, and other environmental variables such as blue light and/or photosynthetically active irradiance incident on the leaves. However, at low canopy densities there is no actual shading of leaves by neighbours. When measured under laboratory conditions, the stem elongation response to far-red light incident on the stem can be shown to have a very short lag (of the order of minutes in small seedlings) but continue for some time after the end of the stimulus (Casal and Smith, 1988a,b).
The photoperception of the lateral far-red light takes place in the growing internodes. In sparse canopies, the perception of neighbours is mediated mainly by phyB and probably sensitivity is modulated by phyA6.