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Short day plants (plants that flower during short days) require a certain amount of daylight to stay in vegetative state. This is why if it is very bright for a few days in winter, dormant short day plants still do not go into vegetative growth because the number of hours of daylight is too small.

18/6 is not a magic number. This is the typical range at which any short day plant will remain in vegetative state while still growing a robust root system. Most species range anywhere from 12 to 17 hours required for vegetation with variation in individual species especially among crops grown at different latitudes. At near-equatorial latitudes, short day crops typically vegetate in the low range where in higher latitudes, longer day periods are required. Compare for example the growing season in Central America compared to Alaska or Argentina. This is also why crops bred for a particular region don't necessarily do well at other latitudes (flower to early/too late).

24 hour light cycles leave no dark period and therefore no time for plants to commit to root growth. The dark period is also when C3 plants give up excess CO2 and other non-photosynthetic activity. One might use 24 hour light periods for a short time if root growth is desired to be stunted and shoot growth to be accelerated. This would not be good for more than a couple of weeks as the shoot growth would expand more than the roots could provide water for.

Day neutral plants like tomatoes will typically do fine in 24 hour light followed by 16-18 hour light all the way through fruiting. If you use 24 hour light at first with short day plants, it works well to cut this back after they have grown to a satisfactory height by 1/2 hour each day for three weeks or to reach a flowering stage.

Personally with short day plants, I prefer going 16/8 for a week, stepping down to 14/10, and then gradually stepping down to 11/13.  The fertilization scheme is updated weekly during this period from N to P to K heavy fertilizer. Nutrients are another issue as short day plants will use more Nitrogen in veg daytime, Phosphorus at night for root growth, and Potassium for flowering. Most charts for nutrients have a gradual change where half grow/half flower is used and with short day plants, this is where the light would be changed.

It is entirely possible to suddenly shift the light from something like 24/0 to 18/6 and then suddenly again to 12/12. Although this is the easiest to do, plants don't necessarily respond well to this treatment, especially for the first couple of days they may not be at peak photosynthetic activity.

so i have been growing indoors for a few years now and i have always grown my plants on 18 hours of light and 6 hours of darkness from seedlings till im ready to flower them. over time i have heard many people mention growing under 24 hours of light untill ready to flower but could not tell me why they preferred 24 hours of light to 18/6 and couldnt tell me the growth difference between the two. has anybody attempted to use both that can tell me what the benefits of growing 24 hours a day be?

Thanks a lot for the post. I really want to learn how to grow plants using hydroponics but I don’t have much knowledge about this method. I appreciate your effort in writing articles or posts about hydroponics which helps me a lot in understanding matters about this amazing method of planting.



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I would also add that the heat created by the lamp is often an issue. Cool-tubes rectify this. Other times it is desirable to have some heat making a hot-spot diffuser a better choice.

I have found that the less air circulation and/or CO2 concentration an area has, the larger the negative effect from overheating. Well circulated CO2-rich environments can stand 95F easily due to the lack of depleted air pockets lining foliage as would be the case in less than optimal conditions.  I have found that growth is actually slowed by low temperatures in enriched, breezy environments. Heat-intolerant plants will not fare well like this and C4 plants do not have the same heat issues as C3.

Orchids will not do well if the heat from the lamp causes a large difference between day and night temperatures.

LED and fluorescent produce minimal heat which makes them ideal for confined spaces.

When you buy a ballast, I have following suggestions:
1. You should buy an electronic ballast rather than a magnetic ballast.
2. It must be UL and CUL approved.
3. The ballast can run both HPS and MH bulbs.
4. Moisture and dust can enter an electronic ballast whith a built-in fan and will damage the ballast. Be sure not to buy this kind of ballast.
5. Consider to buy an electronic ballast with dimming function.
6. Buy an electronic ballast with long warranty.
7. If possible, consider to buy LED grow light.

To buy a grow light, you should know the following:
1. What is the light level required by your crops?
2. What is the size of the grow room?
3. How high can you install the grow light?

Okay, here are pictures of tomatoes and broccoli growing in dutch master grow A+B. The tomatoes are on 3ml and the starts all on 2.25ml A 2.5ml B (or as close to that as a dropper is calibrated to, no pipette or anything). Bottle says 3.5 of each and feeding schedule says something different. I calculated what I wanted on a spreadsheet based on the liquid light.

I've been taking the starts out and spraying with "No Wilt" as seen in the last picture. This is helping a lot. The first starts I tried all wilted. One of the ones that wilted is in the first picture and it is very scrawny as a result.

My medium is about 2/3 large coconut husk chips, 1/3 hydroton.

I have found this brewing recipe calculator to be extremely useful for making recipe's on the fly. They even have a wonderful supply of pre-made recipes and user submitted recipe's.

http://www.tastybrew.com/

If anyone comes up with an ultimate recipe please post it here!

Everyone please read this. It has opened up my eyes to the concepts of incorporating microbiology into my enclosed growing systems whether they be 100% soil or 100% hydroponic and any mixture in between.

http://soils.usda.gov/sqi/concepts/soil_biology/soil_food_web.html

Hello, Lumatek's Dual 600w Digital ballast is two 600w ballasts in one enclosure. it runs a total of 1200w's at around 5.5 Initial amps. I hope this helps in choosing the right ballast for your application.

This is still coming along. I can't seem to find my digital camera so there are no pictures. I think I hit the Floramato formula with Dutch Master A+B pretty well. Using DM for tomatoes seems to be just using 1/10 less than the feed chart calls for supplemented by the liquid light for early development.

The roots are enjoying it. The upside-down tomatoes are a bit etiolated from their container blocking light, but they will grow around that problem soon.