Roots, Repotting, Up-potting and when to do it.

[VerdantGreen]

Hi all, here is a quick guide with some pics to illustrate repotting/up-potting at the best time. Getting a feel for this and getting it right is very simple and you can get more out of your space and plants.
When you repot a plant in a timely fashion you will get a growth spurt... and then if you repot it again before that growth has slowed or stalled, you can ride a wave of growth that gives you extra root mass and a better, stronger plant for flowering.
After a plant has been in its pot for a week, you should be able to carefully put your hand flat on the soil surface with the stem between your fingers, turn it upside down, and carefully lift the pot off the rootball to inspect the root growth. (this gets a bit difficult with pots larger than a gallon or so)
This is an excellent thing to get into the habit of doing with confidence.. because the roots tell you a whole lot about the plant - the ones that grow best and strongest are nearly always the ones with the most root mass.. and the weak, slow ones usually have the fewest roots.
So here are some pics, with my opinion of whether they need repotting and the state of the roots.
Picture first, with the description underneath.

Small pots first... This one is fine, i would leave this in it's pot for a few more days and check it again.
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This one i would say is about ready to be repotted, its 'in the window' for optimum repotting imo but it could still go a couple more days in this pot without it being compromised.

more in the next post.

 

[VerdantGreen]

now some medium sized pots

This one is going nicely but WAY too early to repot.. in fact the rootball would likely fall apart as it doesn't have enough roots to hold it together. This is fine in this pot for another week at least.
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same with this one, fine for probably another week.
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This one has a bit more root growth and could just about be repotted but i would leave it a few more days
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This one is at the about the ideal time for repotting. There are plenty of roots visible and they are starting to have a few layering around the corners but they are not quite matted together yet. This plant will start to slow down in a few days if it stays in this pot

 

[VerdantGreen]

This has been in its pot for too long. First thing to notice is that the roots aren't all white... some are brown which means dead... probably something like fungus gnat larvae nibbling them!
Also you can see they are layered and matted together at the edges and corners. This plant will have already slowed down and will now take a few days to get going again when repotted. I would actually loosen and and break some of the roots to stimulate new growth.. or cut an inch or so off the bottom and sides (also prune the plant top growth back) and repot into fresh soil - i do this with my mother plants to re-juvinate them.

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This one is even worse.. the roots have somewhat died and rotted away and the soil has fallen out from around them.

 

[VerdantGreen]

And some bigger, 5 litre pots:

This is ready to be repotted, but just slightly on the earlier side and would be ok in the pot for a few days longer i think.
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This one is about perfect for repotting i would say. Roots webbing across the bottom and starting to layer at the edges but still loose and not matted together.
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This one is ready for repotting, slightly more roots than the last one but they are still loose but starting to layer. I wouldn't want to leave in in this pot for longer.
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and lastly this one has even more roots and is getting towards being overdue for its repot... but the roots are all still white and although layered at the edges, have not quite stuck together yet. When repotting i would gently pat them around the edge just to get them to come apart a little more, then place on top of the soil in the partly filled new pot and fill around the sides.
VG

 

[GreenAndFast]

Brilliant mate

 

[stiff]

Good thread
Nothing worse then having a rootbound plant and trying to balance it with fertiliser or so because it looks like all the horror pics you've seen about over or underfeed plants.
And in coco that happens super fast

 

[Cakeboy]

very helpful VG, going to try and get used to upending em to have a look. cheers

 

[Creeperpark]

What I use to determine transplanting time is the watering sequence. When my plants need watering every day it's time to up-pott into the next size container. Since I don't want my plant to stay wet too long, it's important not to up-pot into a larger container when the watering schedule is every 2 or 3 days. If one puts a small plant into a too large container the chances for root rot are much greater.

 

[VerdantGreen]

Hi @Creeperpark , i agree that watering frequency is a good indicator.. but watering is also affected by other variables. Also it involves keeping track of what you watered and when - and i have too many pots at different stages doing different things for that. A visual inspection of the roots gives you an immediate, accurate guide.
I also agree that putting a small plant without many roots into a big container can lead to overwatering issues - and also by repotting too early you lose the extra root mass that would have developed before you give them more space in a bigger pot. Roots do not populate soil particularly efficiently (it varies between variaties quite a bit) and a small plant put into a very big pot - i believe you end up with less root mass than timely up-potting.
VG

 

[VerdantGreen]

very helpful VG, going to try and get used to upending em to have a look. cheers

Hey @Cakeboy thanks!
It can be a bit nerve-wracking to start with but it's quite easy to get used to. Main thing is try to avoid attempting it until the plant has been in its pot for a few days to a week so the roots hold the soil together - if it is growing strongly then that probably tells you that the roots are growing.. you may be able to see roots through the holes in the bottom too. If you ever made sand castles at the beach.. remember how you take the bucket off the sandcastle very carefully so as to keep the perfect shape? - do it like that.
I'm a (regular) gardener by trade as well as this hobby, and i have to judge whether plants are worth buying or acceptable, and this is what i always do when plants are del ivered or at the garden centre when buying. Often the plant in a big pot has only been repotted a few days back and is not very good value.. or they have been in the pot since last season and are very rootbound. either way i reject them.
Worst that can happen is you do it too early and the soil falls off your hand and you have to pick it up and put it back in the pot and the plant back - annoying but no harm done because the roots hadn't populated the soil yet. This hardly ever happens when you are used to the procedure .
VG

 

[VerdantGreen]

Another thing to consider is when to put the plant into it's final pot for flowering in relation to the switch to 12/12 lighting...
I can't give you a universal answer to this because there isn't one, it depends upon quite a few factors which i will try to describe here.
As a general rule of thumb i think you want to pot your plant into it's flowering pot between zero days and 7 days before you flip to flower. I find that if you repot and switch to 12/12 straight away (i did this for years) then you tend to get more stretch because the roots suddenly have a lot more space and this encourages the natural stretch that you get as a plant transitions to flower - which can be useful if you able to 'handle' the extra growth and use it to train a scrog for example, or you have headroom to fill. Also, this process probably delays the onset of flowering slightly .. which again means more stretch.
On the other hand if you let the plant root into its final pot for a week or more, the roots have already grown a bit and settled in, and the stretch is a little less explosive. Also this is desirable as you are getting more rootmass before flower starts (root growth does slow down steadily during flower but it doesn't stop until quite late in flower) - on the other side of the coin though.. you don't want the plant to become too rootbound during flower and start to have the issues that this causes.. so you have to balance all these factors.
Try different things in your setup and get a feel for what works best for you. It depends on the variety, and how big the final pot is compared to the pot it is presently in.
eg. The four plants above in the 5 litre pots were all transplanted to 25 litre pots for flower.. and then they were vegged in those pots for 10 days before being flipped to flower ( i suspected this was a bit too long but i went away for a week and there was no alternative) - 2 of the plants were of fairly normal vigor and these have progressed through flowering pretty damn well. The other 2 were high vigor ( Contra D - the two with the most root mass in the pictures ) and these started to suffer from slight issues i would associate with rootbinding at about 4 weeks into flower ) so there are many factors to consider and this you will learn through experience.
You can see the progress of those plants in flower in my grow thread here ( 2 x Contra D, a Chem Zhuzh and a BlueDigiBerry)

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I would also say that it is worth repotting plants up to about 2 weeks in flower... maybe even a few days more , if you think they are going to run out of steam before the end. If you do decide to do this then use a pot that is only sightly bigger than the present one just to give those roots a bit more space (but not too much to cause watering issues with lots of soil that has few roots in it and might stay too wet)
VG

 

[VerdantGreen]

gonna take this post too in case i think of anything else to waffle on about lol.

 

[VerdantGreen]

Another factor in play here that influences root growth is topping and training your plants. Put simply, the Hormone Auxin, a Plant Growth Regulator, is produced in the growing tip of the plant and travels down the stems, inhibiting growth of the side-shoots below it and encouraging root growth.
When you top a plant, removing the main tip (called the 'apical meristem') takes away the source of Auxin - which encourages the side shoots below to grow and also will slow down root growth. Training the plant by bending the main tip down below has a similar, but not so pronounced, effect.
I try to co-ordinate my repotting and topping/training so that the plant has some time in its new pot to root out into the new soil, .. and then i top or train it and let the side-shoots develop. This way will avoid trying to get the plant to do two slightly conflicting things at once.- and it also won't get rootbound so quickly because the root growth will be slower after the topping/training.

VG

 

[grayeyes]

Ok, VG, next question. When you transpot root bound plants do you break up the roots before you put them in new soil?

 

[VerdantGreen]

Hi @grayeyes - Yes, if the plant has started to slow down and suffer from being rootbound then breaking up the mat of roots is advisable... It will stimulate fresh root growth BUT it will probably take around an extra week or so for the plant to respond to that stimulus and get going again with healthy vigorous growth. If the plant is only slightly rootbound you can sometimes just tease the roots apart a bit without breaking them - which is preferable as the shock will be less great.
If the plant is a mother plant and not required for flowering.. it is sometimes better to prune the top of the plant AND remove an inch or so of soil from the bottom and sides of the rootball - and then pot it up in fresh soil - this will take even longer to recover but rejuvinates the plant and reduces it's size too. Perhaps i'll post some pics of that process.

VG

 

[GMT]

I tried that with a lovely gifted bonsai tree. It died . I replace rather than rejuvenate, I'd like to see that.

 

[VerdantGreen]

I tried that with a lovely gifted bonsai tree. It died . I replace rather than rejuvenate, I'd like to see that.

Ok mate i've got some mothers that need rejuving - i'll grab some pics later this week as i do it ! - main thing when removing roots is to also remove some top growth as well.
VG

 

[VerdantGreen]

@GMT and all...
here is an old Bubba D mother plant that has been in this pot for some time and needs rejuvinating:

the roots are old and brown:

plant with its rootball:

So ive taken an old bread knife (or a saw will do) and cut about 2 inches off the bottom of the rootball and an inch off each side, also it is important to reduce the leaves/top growth of the plant ... this balances the removal of roots, reshapes the plant and reduces the height:

and here it is back in the same (washed out) pot with fresh soil under and around the reduced rootball. If you can.. leave a couple of the shorter growth tips on the plant but not essential.

It wants to be put under a fairly strong light - I'll post a pic in a week when hopefully it will be growing back nice and green and healthy. Ive never lost a plant by doing this so hopefully this wont be the first lol.
VG

 

[Creeperpark]

That's a neat way to rejuvenate the soil in an old container. I do that with my horticulture plants. Some of them are over 15 years old and still growing like crazy.

 

[chilliwilli]

@VerdantGreen how long did the moss need to grow? Nice cover crop.