When to use N; When to use P; When to use K

After visiting the local gardent centre, I purchased some Phosphate (Phosphorus Pentoxide P2O5) and some Sulphate of Potash (Potassium Oxide K2O). I was told to use the Phosphate in the beginning (for garden vegs.) on plants as this would the plants produce a strong root system. I was told to use the Potash/Potassium toward the start of the flowering process as this would help the plants develop strong leaves and produce large fruits (or as for favourite lady plants, Big Buds).

Does this hold true for cannabis plants. I have read that Cannabis plantgs use Phosphate throughout the whole growing process.
What about Nitrogen?? I also have some gardent fert. A NPK 12-5-10 (+4) mixture. Should this be used after the start of the veg. process but before the flowering process.
I do not want to overfertalize. I am only interested in quality smoke for myself.
When is the right time for each fert? and should I use pure Nitrogen instead of a mix?

 

Depending on what soil you are using you should not need any fertiliser for at least a month. With Miracle grow soil and other pre fertilised soils you do not need any fertiliser for near enough the full grow. The biggest mistake growers make is adding to much fertiliser. During veg plants use more Nitrogen for the growth of the leaves then during flowering more potasium for the buds. Any decent multi purpse compost will have everthing the plants need already in it. I would forget fertiliser untill you start flowering them. If you want to give them something try maxicrop seaweed extract this can be sprayed on the leaves (foliar feeding) or watered to the soil as normal. This helps with the plants nutrient uptake and encourages a strong root system. It tells you on the bottle how many capfulls to add to water. Try it at half strength. Don't go mad with this though either. Like i said the biggest mistake growers make is seeing a yellow leaf and thinking it must need more fertilser. More often than not yellow and curling leaves are caused by to much fertiliser at the beginning of your grow.

 

Well, my plants are actually about one month old. They got off to a very slow start as I did not have a grow light for about the first 2 1/2 - 3 weeks, relied on sunlight. After being under the grow light they naturally got better but after adding the potasium, the leaves got huge!!!! and lots of new small leaves on lower branches, maybe nothing to do with the potasium but I can't help but thinking that this potasium helped the plants. I am using a compost and mostly growbag mix and did wait almost one month before adding any fert. that is the postasium. I was told to use postasium in the beginning for strong roots but have read that mj plants use postaium throughout the growing cycle. Should I use potash at all, if so, at the flowering stage? or add more potasium?? What about the NPK 12-5-10 (+4) mix? I don't want to use Nitrogen at all if it will make harsh smoke! When, if at all should I add nitro gen?

Yes you are right about overfert. Is potasium a good thing to feed the plants every 2 weeks as long as I flush the plants with pure water 2 weeks before harvest? This is my first time growing and I have been reading a lot and this is one area where I am having some trouble finding info about potasium and postash? Thanks for your help! I appreciate any ideas or comments from anyone!!

 

whoops, I meant the only fert I have used so far is phosporus. This made the leaves huge. I was told this was good for root growth and to use the postash/potasium for flowering. But I have been reading on the net that mj plants use lots of phosphorus. Again, I do not want to overfert. but if I flush the plants well 1-2 weeks before harvest can I use to much potasium or phosphorus? From what I have read using too much Nitrogen will give a harsh taste, that is why I was wondering about using the NPK 12-5-10 (+4) mix?

 

I wouldn't recommend using any fertilizers for your first grow.
You can grow your plants with plain water and potting soil. They may not grow as big, but given the proper lighting, they should be pretty healthy without any help.

The best way for me to describe would be to think like a scientist. In order to be able to do any experiments, you must have a control. You can't know if you have succeeded with your experiment unless you have a control to guage against.

How do you know that it was the potassium you added that cause the explosion of leaves, and not just genetics or a change in the environment (such as artificial lighting)? What happens if your plants start turning yellow, was it the potassium you added, or is your plant starving for nutes or is it overwatered?

After a couple of grows where you only add nutrients when it's required, you will come to be familiar with how far you can push the plants with food and how the plant will react. In the meantime, you are more likely to have a successful crop if you don't add any ferts. You can stunt your plants growth by adding nutes just as easily as you could increase it.

 

In future if you do use any fertilisers buy ones designed for growing weed. Theres hundreds of hydroponic shops on the net that sell fertilisers made for the job. Theres loads to choose from usually you use one sort during veg then swap to another during flowering. Just adding potasium dosn't sound a good idea an excess of one chemical can prevent the uptake of another. Have a look at the nutes at
http://www.hydroponics-hydroponics.com/.
Like nickelbag said just use water for this grow. If its been slow up untill now and you have added potasium there should be enough in the soil to see you through. As your plants get bigger and have decent light you will be surprised at how quickly they will grow probably nothing to do with extra potasium.
As mentioned earlier a weak solution of maxicrop seaweed won't harm your plants I've found it does help bringing unhealthy plants back to life by enabling roots to uptake nutrients more efficiently.

 

Baffoon is correct to suggest getting nutrients designed for growing MJ.
NPK alone is an incomplete fertilizer. There is micro nutrients also.
Potting soil will have all the nutrients the plants will need, but if you add NPK, you must also add the micros or the fert will be unbalanced and you will likely end up with nutrient lock.

You can save your garden ferts for a future grow when you are more experienced and comfortable with prescribing nutes to your plants. Just be sure to use something like micro-grow to supplement the micro nutrients. By then, you will probably decide not to use them however