Nutrient needs based on growth stage

**Cissy** · 11-17-2010, 01:25 AM

I know there must be several threads on the site already where I could find my answer, but I am having no success with my search. So a little help pointing me in the right direction to a thread, a chart, or a simple answer would be much appreciated.

I am using the full line of GH in a DWC system. So I am going to go with what HG recommends as far as the proper mixture. However, I understand that certain elements are absorbed better at certain PH levels. So I would like to adjust my PH accordingly throughout the flowering stage.

Example would be Calcium and Magnesium. Mg is absorbed best from 5.9 and up. Ca is best absorbed from 5.7 and down. While many might just recommend trying to maintain 5.8, which is what I have always done, I would think it to be best to go a bit higher than that when Mg is needed most and a bit below when Ca is needed most. Phosphorous is also best above 5.9 and Mn is best below 5.6, according to this chart: http://www.gardenscure.com/420/attac...ailability.gif

So I was just thinking to let it drift a bit above 5.8 or a bit below at various times, based on the plants needs. Now i just need to know when they need what.

PS - i dont really care about the specifics of the growth stage. just looking to fine tune in flower

ty

**TaoWolf** · 11-17-2010, 01:49 AM

The plants aren't going to need every element and microelement available at the same rate/amount. For example, the rate of nitrogen uptake is going to be higher than the uptake of manganese and magnesium. So while pH may be less than optimal for manganese and magnesium uptake at a middle pH range (for hydroponics), it still works out as far as the plant is concerned - it doesn't need either of those elements as much as it is going to be pulling nitrogen out of solution.

That said if you want to split hairs with pH... the pH normally rises as the plants consume what they need out of solution. So it's very easy to do like you are thinking and set the pH slightly below what you think is optimal, let it rise through optimal, and by the time it gets too high - do a reservoir change and start the process over. You can maintain some control over the rate of the pH rising with the plain water you top off with.

5.8 to 6.2 will cover phosphorous uptake for flowering (that's the range I let my buckets swing through).

**Cissy** · 11-17-2010, 03:57 AM

Originally Posted by TaoWolf

The plants aren't going to need every element and microelement available at the same rate/amount. For example, the rate of nitrogen uptake is going to be higher than the uptake of manganese and magnesium. So while pH may be less than optimal for manganese and magnesium uptake at a middle pH range (for hydroponics), it still works out as far as the plant is concerned - it doesn't need either of those elements as much as it is going to be pulling nitrogen out of solution.

That said if you want to split hairs with pH... the pH normally rises as the plants consume what they need out of solution. So it's very easy to do like you are thinking and set the pH slightly below what you think is optimal, let it rise through optimal, and by the time it gets too high - do a reservoir change and start the process over. You can maintain some control over the rate of the pH rising with the plain water you top off with.

5.8 to 6.2 will cover phosphorous uptake for flowering (that's the range I let my buckets swing through).

thank you!

one thing though, my PH actually has a tendency to drop a little over time. not much but it definitey goes down, not up over time. i have a huge DWC homemade container. i usually start it off at 5.8-5.9 and never let it drop below 5.5, but most of the time it is somewhere between 5.5 and 5.8

**stickybob** · 11-17-2010, 04:11 AM

looks like you have it well tuned in

**TaoWolf** · 11-17-2010, 04:23 AM

If the pH steadily drops, it's *usually* just because the plants are using more straight water for transpiration than they are removing elements from the water to grow (that's why I mentioned gaining some control over pH when you top off the reservoir as needed).

**Cissy** · 11-17-2010, 05:46 AM

Originally Posted by stickybob

looks like you have it well tuned in

I'm looking to fine tune it

**Cissy** · 11-17-2010, 05:49 AM

Originally Posted by TaoWolf

If the pH steadily drops, it's *usually* just because the plants are using more straight water for transpiration than they are removing elements from the water to grow (that's why I mentioned gaining some control over pH when you top off the reservoir as needed).

This drop is very slow and steady. A non issue.

At the end of the day, are you suggesting that there really is no need to start the PH off on one end and gradually, yet deliberately, adjust it? Should I just go with the usual range and not think that anything is being lost in the process? Again, i am trying to maximize potential, not solve any noticeable problems.

**stickybob** · 11-17-2010, 05:49 AM

i fluctuate between 5 - 6 every couple of days - my tank is only 70L and plants are 2 week into flower. My ph tends to drop now so i set it at 6 and leave untill 5 before adjusting, seems to work a treat

**TaoWolf** · 11-17-2010, 06:59 AM

Oh I wasn't trying to problem solve - just pointing out why your pH is likely drifting in a certain direction since it sounds like you want to try and control the fluctuation from one point to another. I suggested a drift range of 5.8 to 6.2 (or 6.2 to 5.8 if you have a downward trend) since you mentioned maximizing potential in flowering - which is when phosphate need increases. During the vegetative phase of growing, a wider drift might be beneficial (such as 5.6 to 6.3).

If you already know your pH trends in a certain direction and how to speed that trend up or slow it down, I would take advantage of that as opposed to deliberately chasing the pH around by adding acids/bases.

My apologies if I'm misunderstanding.