A Watering and flushing tutorial for soil

Green Cross

Well-Known Member
As long as I'm flushing: Here are a couple watering/flushing tips:

Before I begin; It's important to add some pearlite or other porous material (1") to the bottom of your container, so that you have good drainage, or you will have problems with over watering.

I routinely flush about every 6 weeks just to remove toxic salts from the soil, again at the beginning of flowering (to remover excess nitrogen), and again 2 weeks before harvest to remove excess fertilizer.

Wait until your container is really dry before watering and especially before flushing. I used to grow trophy African violets, and they can't handle drought, but MJ on the other hand can't handle too much water. You will never kill a MJ plant watering it a little too late, but water too soon and you can cause the deadly root rot. Let them dry out thoroughly between watering's, especially in flower. The best way to tell if your plant needs water, it to dig your finger into the medium, and if you feel any moisture wait. Eventually you may get a feel for watering, just by lifting the container, judging by the weight of the container when wet/dry.

When you water, do so thoroughly. Some times its necessary to drench the medium twice - 10 minutes apart - before the soil can absorb enough water. Water enough so that 20% runs out the bottom, and you won't have to worry much about salts (from fertilizer) building up in the soil.

Use some common sense here: if it's 100 degrees, and the water runs right through the pot, you should be watering in 2 steps - as explained above. If you have a seedling in a 5 gal container, you'll want to water less, so it doesn't take 10 days to dry out. This is one of the reasons I increase the container size gradually - A seedlings roots will develop better when it goes though a fast wet/dry cycle.

After drenching the container, let it drain, and then tip it up on edge, so that all the excess water can drain out one of the drainage holes. MJ doesn't like having wet feet. This also draws O2 into the root zone.

Don't flush or water again, until the medium drys out again.

The amount of water to use when flushing depends on the amount of fertilizer in the soil, and the density of the soil, but a 1 to 1 ratio water to soil should be enough to remove most the excess fertilizer. If you need to detoxify the soil, due to improper fertilization and watering methods, you may want to use 3 gal of water to 1 gal of soil, and then transplant to a healthy soil mix.
 

nextbigtoker

Active Member
im scared i will do something wrong during flushing and accidently over water my plant, is that possible, since you are putting so much water in the soil?
 

Green Cross

Well-Known Member
im scared i will do something wrong during flushing and accidently over water my plant, is that possible, since you are putting so much water in the soil?
Sorry I didn't see your question earlier.
In the future; if you have a question on one of my tutorials, just PM me and I'll get right to you.

as long as you let the soil dry out prior to flushing, you can flush with as much water as you want, and you won't have to worry about over-watering. It's when folks flush before letting the soil dry out, or flush more than 1 day in a row they get into trouble. :peace:
 

Green Cross

Well-Known Member
Still more questions:

nextbigtoker said:
HELLO FELLOW GREENTHUMB..

I understand usually 1-2 weeks before harvest (usually 70% hairs are red/brwn) your said to flush. 1 week usually for organic ferts like foxfarm.

My question is, like you said let the soil dry out before flush.. you know normal dry.

Then flush with 3 to 1 water every couple days. ( so if in a 4 gal pot, about 12 gal of h20 to flush)...

you don't do this obviously every day for the whole week but maybe every 2 days or so right? i want to make sure i am understanding correctly. then let the last 2 days before chop sit in complete darkness.....

any tips/info i appreciate.. thanks for being around!
Hey Deviozone, good questions, and I'll post this (PM) so others may benefit... No, ALWAYS let your soil dry out between flushing (s).

Did I actually say to flush 1 week before harvest? I'll check after I post this, but the experts say, "you want 14 days minimum for the plant to use up the excess fertilizer." (paraphrasing).

Harvest times vary greatly, depending on the amount of light the plant is receiving and the strain. Indicas typically take less time than sativas, and 1000w lights, or full sun, typically take less time than lower wattage bulbs.

But as far as ripeness is concerned, "70% hairs turning" isn't an accurate indicator of ripeness. I've yet to see a plant where the hairs didn't turn 90% - and pull back into the calyx - before the trichomes started to turn amber (about 3 weeks later(ripening doesn't happen overnight).

Trichome color is the only fail-safe indicator of true ripeness, and this is probably why 90% of growers harvest too early.

I'm sure there's a good harvest tutorial on RIU, but what you need is a magnifying glass, or pocket microscope to view the trichs. Once I start seeing amber I start flushing. 1 part water to 1 part soil. About 3 weeks later you should be seeing plenty of amber (30-50%), but this varies, depending on your light output, and the strain you're growing. If it's a hybrid strain, and the breeder gives an estimate of 65 days, that estimate is based on 1000w lights. If you're growing under 400w lights you can probably safely add 20 days to that estimate, and even more if you're growing under CFL, but I digress. :roll:

This is what you're looking for; trichomes are full (not mushroom shaped), with 1/3 clear, 1/3 cloudy (milky), and 1/3 amber. This bud has reached max THC production and is ready for harvest:


Re Flushing: Only flush when dry, so flush once (1 - 3 parts water, depending on how heavy you've been fertilizing, and how well drained your soil is. If your soil is heavy, and you've been using strong chemical fertilizers, it's going to take more water to flush.

2. Then let the soil dry out again.

3. Then flush again (if necessary), or just water normally with plain water.

There's usually no need for repeated flushings, if you mixed your soil properly (adding 20% pearlite for proper drainage (soil preparation is another tutorial).

Flush once, and then water normally (or flush) until the plant is ripe.

Never flush or water wet soil
 

Green Cross

Well-Known Member
thanks for the good info green cross. + rep
Thanks eagles,

there's more to watering than most people think lol :peace:

I guess I could've added a whole section on water condition, but I didn't think of it at the time.

If your water is extremely hard or soft you may want to PH it, but I've been lucky, I've never PHed my water, and never had a problem.

If you use tap water, let it sit out 24 hrs so that the chlorine has time to dissipate. Letting it stand too long will cause it to go stale (from lack of oxygen), so I keep an aquarium air stone circulating 5 gal buckets.

If your water is treated with "clorimine" it won't dissipate, and may harm your plants.

Purchasing water from a water vending machine is an option. Some walmarts have them near the front of the store. Bring your own containers.

You can also collect rain water, but it may contain pests, and pollution.
 

Green Cross

Well-Known Member
Now that it's almost winter I thought it would be good to add this:

It's best to water in the morning, so the stems can dry out during the day (while the lights are on). but I've noticed now that the weather is getting cooler, the water is pretty darn cold, and cold water shocks roots, and - in turn - slows growth.

If you keep water on standby - as I do - to allow chlorine to dissipate:

1. Run an air stone in it to keep it oxygenated. Roots need O2

2. Add a fish tank heater to it - in the winter - to prevent the roots from being shocked, and your plants will love it. 70 degrees F is fine, but you can go up to 90 if your grow room gets really cold at night.

I haven't yet picked up one of these but I intend to...


More on soil temperature from Ed Rosenthal:

"Marijuana is low-temperature tolerant. Outdoors, seedlings sometimes pierce snow cover, and older plants can withstand short, light frosts. Statistically, more males develop in cold temperatures. Low temperatures, however, slow down the rate of plant metabolism. Cold floors can lower the temperature in containers, thereby lowering root temperature and slowing germination and plant growth. Ideally, the medium temperature should be 70 degrees.
There are several ways to warm the medium. The floor can be insulated using a thin sheet of styrofoam, foam rubber, wood or newspaper. The best way to insulate a container from a cold floor is to raise the container so that there is an air space between it and the floor. Overhead fans, which circulate the warm air downward from the top of the room also warm the medium.
When the plants' roots are kept warm, the rest of the plant can be cooler without danger. Heat cables or heat mats, which use small amounts of electricity, can be used to heat the root area. These are available at nursery supply houses.
When watering, tepid water should be used. Cultivators using systems that recirculate water can heat the water with a fish tank heater and thermostat. If the air is cool, 45-60 degrees, the water can be heated to 90 degrees. If the air is warm, over 60 degrees, a 70 degree water temperature is sufficient."
 

Green Cross

Well-Known Member
Nice write up.
Thanks pastafarian :joint:

RockstarEnergy said:
hey man hows it going?

you say in the watering thread only flush when the soil is dry. i have a case of nute burn and its getting worse but my soil isnt completely dry yet. my moisture meter is at 5(out of ten) so its not dry but not drenched. is that too wet to flush cuz its kind of an emergency?

thanks
Yeah man it's better to wait for the soil to dry, because more water is also going to cause more nutrient uptake; It can't be avoided; but by waiting you also avoid an over watered condition. :joint:
 
what if i had been using 3 month time release fertilizer for the soil? how effective could i actually flush the soil? do i release more nutes everytime i water? and
 
I also would like to say thank you as well,I was hoping I would find the info I needed here,Iam new here and I am not to good with computers and I do not mean ti butt in but I also have a few plants that will need to be flushed soon.The Trichomes are half cloudy and half clear,so if I understood what you all said I should wait untill 10% of the Trichomes are amber before I flush them,is this correct ? Again I am very sorry if I butted in to your conversation,I just want to be able to grow fine bud,I am tired of buying it and the money I give these people may be used for harming people,I know this may sound crazy but brothers and sisters the world is not the same as it was before 9/11 and there people who hate us and our way of life and I do not mean the cops,Iam talking about Islamic mother-fu--ers
 

wild95cat

Member
I also would like to say thank you as well,I was hoping I would find the info I needed here,Iam new here and I am not to good with computers and I do not mean ti butt in but I also have a few plants that will need to be flushed soon.The Trichomes are half cloudy and half clear,so if I understood what you all said I should wait untill 10% of the Trichomes are amber before I flush them,is this correct ? Again I am very sorry if I butted in to your conversation,I just want to be able to grow fine bud,I am tired of buying it and the money I give these people may be used for harming people,I know this may sound crazy but brothers and sisters the world is not the same as it was before 9/11 and there people who hate us and our way of life and I do not mean the cops,Iam talking about Islamic mother-fu--ers
Well said!!!

"You will never kill a MJ plant watering it a little too late..."
WHAT???!!! Uuhhh, YES YOU WILL! I waited an extra day longer than the previous watering on one of my plants, the next day 8 hours later, it was almost 100% wilted up and dead. I should've watered it on schedule. And btw, as long as you mix 30% perlite into your mix, and put an inch or so of it at the bottom of the container, you'll be fine with watering plenty. I flush after each feeding to bring my Ph back up from 4.5 to 6.5. I've never seen greener plants...and I've only been growing for 9 months!
 

Lip G.

Member
Ya man ... excellent info .. took me a few waks at google, till I first entered Rollitup and second try BAM here it all is . thx a lot! Just did two clearing flushes Sunday and another Sunday ago and will def wait longer than the week, as I did last time .. great clarification for me ... DANKA! (she was near but I was getting impatient .. she'll be dry on the bottom before her final drink.
 

Fractured but whole

Well-Known Member
Ya man ... excellent info .. took me a few waks at google, till I first entered Rollitup and second try BAM here it all is . thx a lot! Just did two clearing flushes Sunday and another Sunday ago and will def wait longer than the week, as I did last time .. great clarification for me ... DANKA! (she was near but I was getting impatient .. she'll be dry on the bottom before her final drink.
it's great for 8 year old information that is also,wrong.
 
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