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My indoor plants are fairly disconnected from the outside: the temperature and humidity are controlled and they are under strong artificial lights 18h/day.

Should in any way care about seasons? For instance, my fertilizer says to apply twice per month during the growth season. Do I have a perpetual growth season or do plants take a break by themselves anyway? (Alternatively, do they need one?)

In case it matters, I'm growing right now: basil, chives, mint, sage, mango (1' high), avocado (1' high), a few houseplants, tomatoes (seedling), lavender (seedling), cosmos (seedling).

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Stormy has a nice answer (especially on fertilizer part), but I am going to add some general concepts.

Temperate plants usually needs different seasons to grow naturally. But we don't cultivate them for their needs, but for ours.

On your list:

  • basil, chives, mint, sage: we try hard not to have them flowering, so by not giving them the cold season and trimming the flowers (basil) we force them to continue with the green phase. So it is ok (for us) to hide them the seasons. If you want to get seeds (e.g. chives) or to renovate the plants, you should provide them with the cold season, and let nature to complete their cycle finally

  • tomatoes, avocados and mangos are more tropical (so less sensitive to seasons). Tomatoes are somewhat special: they continue to produce flowers, so without seasons, the plant will continue to produce, but then it will eventually die. You could give some more seasonal climate, to have it behave like perennial, but I think it is better to plant them every year, and keep them as long as possible. The other two have a cycle, so a cold season will help them to find when to produce flowers and so fruits. In hot places, you can force them also to have two fruit season per year, but deceive them with a fake extra cool "short season".

  • cosmos and lavander: As far I know, they need some cold period to produce again a lot of flowers, but I think it could be also short, so you can give them the cold season when their are losing energy.

So cold season is often needed, but for some plants it could mean just few weeks.


Note: some plants use length of day or other internal clock and not only cold days, but AFAIK none of the plant in your list. [an interesting story on internal clock: in a nearby botanical garden, they have few South African plants which flower in the same period as in South Africa, so with a shift of 2 seasons if we look temperature or day length. AFAIK nobody know exactly what process drives this]

  • Well put, Giacomo. Daylight/ dark...cold periods...proper fertilizer proportions...and more dictate success. – stormy Nov 15 '17 at 8:07
  • One thing I'm wondering about here is: Should I "manually" introduce the cold season? By putting them .. outside? Or is watering/fertilizing them differently based on the season enough to make them think they're in the "cold" season? – Sebastian Aug 3 at 19:56
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As long as there are no indicators of seasons, your plants are on the seasons you dictate. Do you have your plants on timers and are your plants protected from any other lights to include daylight through the windows? !8/6 is great for young plants and vigorous growth. That season is late spring early summer. The tomatoes and Cosmos need some tweaking. Lower nitrogen in proportion to the phosphorus and potassium. Reduced fertilizer application. And gradually reducing the daylight hours versus dark hours to 12/12. This replicates going from summer to late summer to fall and promotes flowers/fruits.

The other plants are leafy greens, chives, basil, mint, sage (grown for vegetation not flowers and fruit). They do best with Nitrogen equal to Phosphorus and Potassium. They will do fine even at 12/12 for the tomatoes.

Cosmos are an annual and will be happy with low nitrogen the entire growth and flowering period. Too high nitrogen and you'll get lots of Cosmos leaves tiny buds few if any flowers.

What are you using for fertilizer? Twice per month? How do you water? Is your grow room completely protected from light outside the grow room? Just a little light or peekaboos will confuse your plants. What soil are you using? Plants rely on stability. If their environment is not stable (getting 18 hours of light and 6 hours of dark...changing to 12/12...then all of a sudden getting bright light during the middle of their dark cycle that is one instance of instability, change in temperatures and daily temperature differences...) As long as your plants get stability in everything, they'll be happy. What are you using for soil? What kind of lights are you using? Are you able to keep temperatures no lower than...55F and no higher than 80F? Are you using fans? Do you have a way to pull fresh air in and push old air out of the space? The more artificial your garden the more input you will have. Less margin for error.

You just have to send a picture or a bit more information on your plants, garden and maintenance practices. What fertilizer you are using and what kind of soil? How do you know when to water? Your plants are very different in their needs. How old are your plants? How long have you been growing your plants? A few of your plants are annuals, a few are perennials, a few are woody perennials...all with different needs. Are you able to make two rooms out of the one?

  • Thanks for your detailed answer! You gave me more info than I asked for :) It's true that I have to remember other factors like different fertilizers for different plants, photoperiod, airflow... but I just wanted to know if the actual seasons had an impact or if I had to create a "slow" season artificially. – comeauch Nov 14 '17 at 11:54
  • However I appreciate your help! I'm using a no-soil mix which has no nutrients, a generic 24-8-16 feed (tomatoes and cosmos are still tiny anyway so they don't get anything yet anyway), I water them according to their needs I guess, at least I try! I have a 400W metal halide lamp and they would receive some diffuse light were I to switch to fewer sunlight hours, which is something to keep in mind you're right! – comeauch Nov 14 '17 at 12:03
  • I'm curious about annuals/perennials/woody perennials having different needs? They're all bunched together (in pots) and receive the same amount of light... I also never adjusted pH (and probably killed a rosemary plant this way, as I tried a few watering schedule and it just wouldn't stop dying) – comeauch Nov 14 '17 at 12:03
  • You need to go look up and get to know each type of plant you plant. Some plants have to have more moisture than others. Flowering and fruiting plants need less nitrogen in proportion to Phosphorus and Potassium. I have a great pH meter but I always have two other ways to test pH. To make sure I understand the pH. Annuals need their flowers cut off regularly. Plants love bunched together, just makes it tougher to meet individual plant needs. Water only when the plant and pot feel lighter. You've got a great experiment going, you will learn an awful lot! – stormy Nov 15 '17 at 8:03
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    Thanks stormy! I'll add pH testing/adjusting to my skillset :) – comeauch Nov 15 '17 at 12:17

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