LED Lighting

Hi Guys and fellow growers

Ok , I have not long switched from HPS (sox) to LED lights , in my old set up I had 6 400W HPS in my number 2 bud room which is 10.5m square and in my number 1 room i which was 3.75m square I had 4 x 400W HPS

I have now changed over to LED in room 2 i have 1 x 450W 4 x 300w and 4 x 120w , the irst two are fan cooled . if you imagine a cross with the 450w in centre then the 300w making the cross then the 120w filling in the corners. I did it this way on advice from supplier to get the ideal light spread from the new lights

In bud room one its just two 450W lights simpler

Both rooms have intake and extraction fans 6inch intake and 1 4 inch for every 4 plants , there is also a large circulting fan in each along with a high level co2 slow release system. I have also got insect killers in each.

I grow in John Innes based compost in grow bags. I use a weekly pot ash based feed called chempack No 3 ( blue dissoluble feed)

I have moisture meters in 30% of plants and light meters and pH testers , all are good , room tempis a steady 75.9 degrees

Now my problems are these

slow bud development about 50% longer and worryingly the shading leaves at the base of the plant go brittle brown and then wither off,

I have also a problem now with black fly.

Now when i contacted the supplier of lights they said to try a full 24hrs cycle to hasten on growth , but this seems to only make the plants grow taller and not bud

I had very few probs with HPS just the normal deficiencies that could be sorted

The strains I am using are blue cheese , big bang and white skunk

any thoughts

andy (KiltyK)

If you are having fungus gnats (black flies?) you are probably over watering and that can also be the cause of spots on your leaves. Other things can be contributing to nutrient lockout/deficiencies or toxicities/nutrient burn, this is why knowing the PH and or nutrient concentrations are important as well as if the soil is too wet for too long and or too often which usually contributes to fungus gnats, root damage and nutrient deficiencies.

This is what I know so far, fill out the rest, be as accurate as possible…

ILGM Support Tickett

What is the strain? – blue cheese, big bang and white skunk
Indoor or Outdoor? – indoor
Size of space? – number 2 bud room is 10.5m square and number 1 (grow/veg room?) room 3.75m square
Soil or Hydro? Medium used? – (Soil?) something in John Innes based compost in grow bags
Type of nutrients used? NPK? PPM levels? – a weekly pot ash based feed called chempack No 3 ( blue dissoluble feed)
Temperature? – 75.9 degrees (Fahrenheit?)
Humidity %?
Light system/watts? – room 2 have 1 x 450W 4 x 300w and 4 x 120w LEDs, In bud room one its just two 450W LEDs
Vegetative Growth season or Bloom/Flower season? Number “weeks/days” from start of veg growth or into flowering?

Knowing the PH of the soil is still very important, knowing the PH of the water you use is very important, knowing the details of the NPK values and nutrient concentration of your nutrient regiment is still very important. We see so many different people using so many different soils or fertilizers you can’t assume we know what is in them or are familiar with absolutely everything out there, and if I had to do my own Google search on everything for everybody I wouldn’t have any time left over to get back to anybody. I assume you are still in the first weeks of the vegetative light cycle/season? Any other details in the list could help.

Ok here goes as best I can

NPK 20:20:20 & Trace Elements

20% Nitrogen + 20% Phosphorus + 20% Potassium + 7 Essential trace elements

PH is sitting at 6.5

The compost is as follows

The Ingredients

The function of each of the ingredients in John Innes is briefly as follows:-


Loam is the most important ingredient in the compost as it provides the main "body" of the compost. It also forms the base of plant nutrition by supplying clay, which has a cation and anion exchange capacity, that is, it absorbs and releases plant nutrients as required. Loam also contains essential micro-elements and some organic matter which provides a slow release of nitrogen to the plant.

Sphagnum Moss Peat in the John Innes Compost increases the total porosity and improves both the aeration and the water-retaining capacity. Peat decomposes slowly into humus.

The coarse sand or grit is used as a physical conditioner to allow excess water to drain from the compost and thus prevent water-logging. It also helps to provide stability for larger plants.

The compound fertiliser in John Innes Compost provides a wide spectrum of plant nutrients needed for balanced growth, including :-

    NITROGEN - for top growth
    PHOSPHATES - for root growth
    POTASH - for flowering and fruiting
    TRACE ELEMENTS - for optimal growth, colour and (where appropriate) flavour

Nutrients are typically sufficient for 1-2 months of growing, after which time additional proprietary feed should be given. 

I have plants at all different stages seed to flower to bud from 1 weeks in to 14 weeks in now

the poly pot bags are individual 10L bags

Humidity is less than 25%

I can send or post pictures of the crispy shading leaves

The black fly are no bigger than the normal aphids or white fly we called the white green and black fly.

I spray every 4 weeks with insecticide which also kills spider mite

I hope this helps and I am sorry if I didnt give enough infor in first place , as you say some us assume too much

thanks again


The flies are probably a sign the soil is too wet, we call the little black ones fungus or soil gnats, as that is where they live and breed, the larva live in the too wet soil and eat fungus and rotting roots that have drowned from the too much water. PH seems good, most everything seems good. I’m going to have to say it sounds like the roots are staying too wet. You probably need to amend the soil in the future with 40-50-% perlite to get more oxygen/air to the roots. Maybe try getting used to the feel of the weight of the container when it is fully saturated with water compared to when it is nearly fully dry to have a better idea of when to water and let the soil dry out a lot. Over watering is one of the most common problems we see, almost everybody does it in the beginning.

A lot of insecticides can contribute to leaf burn as well. Indoors with the temps under control, under 76F/25C you normally won’t get spider mites, they don’t like cool weather. bright yellow sticky traps are better for keeping the fungus gnats under control, they should diminish in number significantly if the soil isn’t staying too wet.
You should get a EC/TDS/PPM meter to test the run off of the soils nutrients to see if that is too high or you can get a soil probe that also does nutrient strength readings of the soil.

TDS/PPM meter:


4 in 1 soil probe:


see this thread for additional info on the soil probe and testing


Many thanks for the info , ill see if keeping the soil dryer helps

I have been growing for a few years now and I said I used to use HPS lighting , and all was good , had the grow room on Metal halide and fluorescent lighting ,these probs have only came to the fore since changing over to LED

I used to water everyday on HPS lights as they used to dry out the plants quickly I still like to do a flush out of plants once a month rough up the soil and soak till the bags are pushing out water , One thing I forgot , the plants all sit on a raised platform to allow over watering to spill out. With LED lights i water twice a week once with feed as stated on packet and once with spring water (carbonated). I also have bowls hung up higher than plants with CO2 tabs in with again spring water activating the tablets , I was told , rightly or wrongly to give as much CO2 as possible during light hours

With the insecticide I am concentrating on the grow medium itself… regarding the fly killer its electric like you get in kitchens and it amasses a pile of flies and moths if they get in ,

Do you recommend I go back to a 12/12 cycle and reject the supplier of lights idea of constant 24 hr lights on ???

lastly Many thanks for taking the time to answer me , I was in another group and not a peep came from there

I have sent a mail to see if you dispatch seeds to the UK as I feel that this is a unique place for growers

Once again Stoner many many thanks

CO2 is great for the leaves, and yes it is only needed during the day/lights on. CO2 rich water should never be added to the soil. The roots need oxygen 24 hours a day.

Yes LEDs will not make the room as hot and the plants won’t use as much water. This is likely the reason for the differences you are noticing.

If you don’t want the plants to start flowering yet, do not do 12 hours of darkness yet, 24 hrs of light is not necessary and returning to 18/6 for veg would probably be best.

Sometimes I proof read after I have posted and make many edits which may come after you have read an unedited version, I may have added more info in the above post, make sure you didn’t miss anything and check above again…

Our shipping on seeds is very fast to the UK , USA or Australia and many more places.