repotting

How often is it necessary to remove a plant from its pot, rinse off the old soil, and put new potting soil in? Do the pots have to be scrubbed when this is done? My plants look fairly good, but could be better.

I always draw a distinct difference between repotting & simply potting-up. I think you can pot-up just about any time with little in the way of ill effects - not so, with a repot, which includes a soil change & root work.

Tight roots are first manifest in a lack of extension of the plant - it doesn't grow longer. Smaller leaves (reduced photosynthesizing area) and foliage loss beginning at the plant's interior and progressing outward so most/all new growth is concentrated near the meristems (growing tips) usually accompany or closely follow the lack of extension. A general decline or loss of vitality should also be expected in plants grown tight.

You should prevent this from happening by regular repotting and root pruning where root pruning is appropriate. How often depends on the genetic vigor of the plant and it's vitality. IOW - how fast it grows. Some plants really should be repotted annually, and others may go 2, 3, or more years between root work & repotting.

The result of a full repotting is actually rejuvenating. I have found that plants that were in need of repotting and that were repotted will sulk for a short time, but will almost always catch and surpass their unrepotted counterparts before summer's end. Most tropical houseplants are best repotted in the month before they will see their most robust period of growth.

Al

When I repot a plant, I just take it out of its pot, remove a bit of dirt, then pot it in a pot one or two sizes larger. No larger than that. You may want to remove the plant from its pot and check to see if the roots are healthy. If not, remove those that aren't plant it in the same size (clean) pot that it was in. Putting it in a larger pot can be damaging to the roots.

Plants need repotting when the roots have completely surrounded the soil and no soil can be seen.

How do you water?. Plants should be watered from the bottom. Stand the pot in 1" of water. Pour a bit on the top soil to start the syphoning action. It will draw moisture from below and throughly moisten the rootball.

I think I'll take a second to disagree .... but I'll also explain why.

You don't make the distinction between repotting and potting up. What you described is essentially only potting up, and there is a difference between that and a repot, which includes removing all or most of the soil from the root mass and pruning roots if that rejuvenating step is appropriate.

How large a container needs to be, or CAN be when you repot/pot-up, and how much soil a planting needs/will tolerate before drainage & saturation is an issue depends on the 3-way relationship between plant mass, container size, and soil type. We often concern ourselves with "over-potting" (using a container that is too large), but "over-potting" is a term that arises from a lack of basic knowledge about the 3-way relationship noted, which should logically determine appropriate container size(s).

It's often parroted that you should only move up one size in containers when "potting-up". The reasoning is the soil will remain wet too long and cause root rot issues, but it is the size/mass of the material and soil type/composition that determines both the upper & lower limits of appropriate container size - not consecutive volume progression.
Plants grown in slow soils need to be grown in containers with smaller soil volumes so that the plant can use water quickly, allowing air to return to the soil. This (smaller soil volumes) and the root constriction that accompanies it will cause plants to extend and gain o/a mass much more slowly - a bane if rapid growth is the goal - a boon if growth restriction and a compact plant are what you have you sights set on.

Conversely, rampant growth can be had by growing in very large containers and in very fast soils where frequent watering and fertilizing is required - so it's not that plants rebel at being potted into very large containers or volumes of soil per se, but rather, they rebel at being potted into very large containers with a large volume of soil that is too slow and water-retentive.

We know that there is an inverse relationship between soil particle size and the height of the PWT in containers. As particle size increases, the height of the PWT decreases, until at about a particle size of just under 1/8 inch, soils will no longer hold perched water. If there is no perched water, the soil is ALWAYS well aerated, even when the soil is at container capacity (saturated).

So, if you aim for a soil composed primarily of particles >1/16", there is no upper limit to container size. The lower size limit will be determined by the soil volume's ability to furnish water enough to sustain the plant between irrigations."

You can grow a very small plant in a very large container if the soil holds little or no perched water (no saturated soil).

I respectfully disagree that watering from the bottom is good practice - especially if done consistently - and wetting the top of the soil will not facilitate any "siphoning" action. This watering method guarantees accumulation of salts from both fertilizer solutions and irrigation water, because no salts ever leave the soil unless you flush them out or the plant uses them. Watering copiously from the top allows soluble salts in the soil to be dissolved into the soil solution. The extra water that exits the drain should not be allowed to accumulate in a saucer - instead, the water should be allowed to drain immediately from the soil so the salts it contains don't have a chance to take part in nature's balancing act (isotonicity) for the different levels of salts in solution. IOW - salts flushed from the soil and in the saucer will equalize in strength with the salts in the fresh water in the soil, negating your efforts to flush the soil.

Al

There is one problem with only watering from the top. If the soil in the pot has become too dry, the soil will shrink from the sides of the pot. Then, when it is watered from the top, the water runs down the sides and don't penetrate the rootball. Water from the top, then allowing the plant to sit in water until the pot feels heavy assured a more complete watering of the whole rootball. And top watering will cause a siphoning action. It will draw water upwards. Try it!

You can also REPOT a plant by taking it out of the pot and cut out 2 vertical l wedges from the rootball, then place it back in its pot and fill the cut out wedges with fresh soil. I have done this when I wanted a plant to remain in the same size pot. That too will rejuvenate a plant. I never remove all the soil from the roots, and disagree with that practice. Why disturb roots more than you have to. Cutting wedges is less traumatic for a plant.

Slow, fast soils. I have never heard of those terms. All soil should be welldraining. There are sandy soil, humusy soil, jungle type soil, and many mixtures in between. There is light soil and heavy soils. Then there are those that dry quickly, and others that retain moisture for longer periods.

Peat and bark based soils only become hydrophobic when allowed to dry down below about 35% moisture content, so if your soil is pulling away from the container sides & is water-repellent, you're allowing it to become too dry. IF it does happen to get to dry, the proper remedy is to water once & allow the plant to rest for a few minutes. Water again and the soil will no longer be water repellent.

Whether you should or shouldn't remove all the soil during a repot depends on the plant, but there are few plants that don't tolerate bare-rooting well if you repot at the appropriate time. I regularly bare-root almost everything I repot (and I'm in the middle of some 100+ spring bonsai repots. While cutting wedges is an effective method of replacing a portion of the soil during as repot, the practice should be reserved for the very few plants that don't tolerate bare-rooting well. The reason is, it's not a good thing to have two different types of soil in the same container.

A 'slow soil' is a very common reference to one that is comprised of small particulates, is heavy and drains slowly - something to be avoided. A 'fast soil' is one that drains quickly & is well-aerated.

Al

it's not a good thing to have two different types of soil in the same container.???

I doubt very much that a plant cares one way or another. Mine grew even better with that extra fresh soil. If it is a concern, you can use the same type of potting mix that is in the pot originally.

Simply put:
"fast soil"=well drained soil
"slow soil"=non-draining soil

Most, if not all, good quality potting soil that are on the market are well-drained.

You ask/said: It is not a good thing to have two different types of soil in the same container.???

When you have two different types of soils in the same container, one is usually too wet, the other too dry. Often, the reason you you have two different soils in the same container is because you have potted up w/o bare-rooting and removing the old soil. The old soil hardens and calcifies making it difficult for fine rootage to penetrate the hard soil. Soil can harden to the point that roots can no longer lay down cells in the cambial tissues and water/nutrient transport is shut off. So you see, there are multiple reasons why we should NOT have different types of soil in the same container and why it IS advantageous to bare-root an extremely high % of plants when we repot. I haven't even touched on the physiology of exactly what happens, but if you understand the difference between the ontogenetic age of tissues and the chronological age, I needn't explain further. If you don't understand, please ask and I'll fill you in.

The reason that bonsai trees are able to live perfectly healthy lives over sometimes hundreds of years in small containers is due to one primary fact - bare-rooting and attention to roots.

"Mine grew even better with that extra fresh soil."

Mmhmm .... but because it put on a little growth spurt is no clarion call to continue the practice in the face of evidence that there is a better way, unless you're happy with the "It works for me" frame of mind and aren't further interested. If you're happy, that's fine with me. What I'm writing here is for the good of the forum - so they can see and judge our arguments on their merit. Plants that are only potted-up are in a general, long-term state of decline, even though they briefly show increased vitality for a short period after potting-up. If you don't understand this statement - ask, and I'll show you a chart that makes sense.

"Most, if not all, good quality potting soil that are on the market are well-drained."

I respectfully disagree. Most commercially prepared soils that come from a bag have marginally acceptable drainage characteristics when fresh, and quickly collapse with use. They may lose only about 25-50% of their aeration in the first growth cycle, but will nearly completely collapse in the second. Bark-based soils, however, will last approximately 4 times as long as a peat-based soil. A soil based on equal parts by volume of
pine bark
Turface or calcined DE
crushed granite
will last indefinitely, retaining structure/aeration far longer than any prudent interval between full repots.

"If it is a concern, you can use the same type of potting mix that is in the pot originally."

Most of the people I talk to are interested in improving their soils, not simply adding to what has already been proven problematic. If the soil is compacted and collapsed, adding to it only prolongs the journey toward the inevitable.

"I doubt very much that a plant cares one way or another. "

Of course plants don't "care", but everything cultural 'matters', for plants. Plants are reactive organisms, endowed with the potential to grow at a particular level of genetic vigor, but limited by their cultural circumstances. When you diminish the favorability of the cultural conditions a plant has to deal with, you limit growth potential. Limit it enough, you induce stress. Stress turns to strain. Strain uncorrected always leads to the death of the organism.

I enjoy soil discussions, and what I offer is based not only on years of practical experience, but on sound scientific principles and plant physiology as well.

Take care.

Al

This message was edited Apr 5, 2009 4:04 PM

where is it?

Tapla, since you mentioned bonsai, I want to "tap" your brains about them. I have a few which are my pride and joy. I recently acquired a fujian tea plant which I think already needs re potting. When watered the plant and soil rises vertically out of the pot for half-inch. I think this is weird. Also there are good sized roots coming up the sides of the pot. Any help you can give me will be appreciated. K

Thank you, Al, for such a brief but thorough description of the effect of correct soils and planting. I guess soil is the incorrect term, and I should say media. I try to keep all kinds of supplies on hand to amend or create according to the plant I'm working with. You are very clear with what you've said.

K - It's probably already a breach of etiquette for me to be discussing soils at length on Erlyburd's dime. ;o) If you contact me off-forum, I'll provide your answer(s), unless Erlyburd thinks the discussion is germane to this thread. Or ask here & I'll reply promptly: http://davesgarden.com/community/forums/t/719569/

"Soil" is fine, Mama. Anything a plant is growing in is soil. Media is just another name for the same thing. There is something of a tendency toward referring to mineral soils (garden soils, topsoil) as "soil" and container soils as media, but it's a very fine point & not something I would even think twice about. When someone says "dirt", though, I already know I have my work cut out for me. ;o)

Al

Well, since most of my "gardening" has been restricted to containers over the years, I suppose I'm more inclined to use the "medium" term. I truly appreciate all that you have put out on this thread, and seriously doubt that Erlyburd would resent anything you have had to say since it's all so educational! - Lynn

I sure would like to learn some more about this.

About what, JB?

Al

Soils/soiless mixing. And I never really knew a thing about "bare root" repotting. I had only done it on plants that obviously had the wrong soil. I usually just removed as much as I could without "hurting" the roots. I was taught to turn plants upside down and tickle the soil off of the top and "topdress" every year, clean off the rootball as above and repot every 3 years.
It is fascinating to learn the "proper" ways to do these things after having done them "wrong" for 50+ years.

There is a discussion here you can read through that should offer some insight. We can easily expand the discussion to include repotting if anyone wishes to take it in that direction.

http://davesgarden.com/community/forums/t/796311/

Al

What a great thread you've linked us to! Thank you so much! My plants thank you too!

Tapla, you may "jump on my dime" anytime. I have learned so much from you. Thank you for sharing. I love learning from all of you, even from the questions you post.

Earlyburd