In article ,
P van Rijckevorsel wrote:
Pascal Bourguignon schreef
Has the experiment of growing plants under the light conditions of the
Moon surface ever been done? What would happen if you tried to grow
normal plants with lights on for 14 days and off for 14 days?

* * *
This will depend on exact circumstances, but put like that plants will grow
as much in a day no matter how long it lasts (24 hours or a month)

Surely they'll grow more in 14 days of constant light than in 12-24
hours of same, but the 14 days of darkness will be very harmful for
most plants at growing temperatures. Prolonged darkness causes
etiolation and yellowing in all growing plants. If I leave
something on the lawn, the grass underneath takes only a few days to
look unhealthy, and two weeks would kill most of it, except, of course,
in winter when the plants are dormant. You can kill most weeds, or set
them way back, by use of light blocking mulches.

Constant light can be helpful when plants are in a vegetative state,
but if you do or don't want flowering, you have to control night
length. For example, short nights (long days) will make lettuce and
most brassicas (cabbage family vegetables) go to seed instead of
producing leaves, which is undesirable. Many ornamentals (and
fall-flowering weeds) need long nights (short days) to stimulate
flowering. I don't know which vegetables are in this group because
most of my experience is with a cold temperate climate. I do know that
beans (Phaseolus) had their short-day-flowering requirement bred out of
them as agriculture moved north from Mexico to southern Canada in
pre-Columbian times. Day length requirements could probably be bred
out of a crop, possibly very quickly by genetic engineering techniques
once the relevant genes are idenitified, but you aren't going to have
as easy a time getting around the fact that most plants will use up
their reserves and begin to die well before they've survived 14 days of
darkness.

Considering the difficulties of building a transparent structure that
is strong enough to resist vacuum and meteorites on the moon, I think
it would be much more practical to have surface solar collectors to
generate electricity to power lights to grow plants. Obviously, you'd
need some method of energy storage for the lunar nights, but growing
crops under artificial lighting is a solved problem. For example,
vegetables have been grown in deep mines in northern Ontario, taking
advantage of the natural heat at depth and the cost of supplying
vegetables in reasonable condition to remote areas with too short a
season and too little heat to grow them on the surface profitably.
IIRC, these projects mostly produce tomatoes and cucumbers, but there's
a lot of developed technology for growing lettuce in surface
greenhouses with supplemental lighting in winter at higher latitudes in
Europe where less supplemental heating is needed in such structures
than in Canada.

Note that your lunar garden provides the valuable function of removing
CO2 from the air as well. Many plants grow better in elevated levels
of CO2, and it's sometimes used commercially to increase growth in
greenhouse lettuce crops, usually by burning propane.

Btw, you might consider how else this lunar colony is getting its
energy. Is it all solar, or is some derived from e.g. a nuclear
reactor? In the latter case, there may well be plenty of energy
available to power lighting for plants.