When to repot in mild-winter climate

jenn(SoCal 9/19)October 15, 2011

I'm suddenly with lots of extra time on my hands and lots of potted plants that need re-potting into new soil and/or larger pots. I would like to start re-potting now. Some of the plants will be planted in the garden within a month (Lemon Verbena, Nagami Kumquat, Meyer Lemon).

If we get any frost it's usually not until January or February, and fall is our best planting season. Does this also apply to potted plants? I seem to recall that potted plants should be re-potted in spring.

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tapla (mid-MI z5b-6a)

I'm confused. If you're going to plant out within a month, why repot now?

Rule of thumb: Temperate plants that employ some sort of dormancy mechanism, whether needed or not as dictated by climate, are best repotted in the spring but can be repotted in the fall or winter IF the roots will be protected from freezing temperatures.

Tropical perennials (houseplants) are best repotted in the month prior to their most robust growth period. In most cases that would be Jun & Jul.

Citrus are best repotted in early spring, but can be repotted in the fall or even as the plant is winding down from a period of robust top growth.

Houseplants are generally at the lowest energy level of the growth cycle in spring, so try to avoid repotting in winter or spring. They recover best when they have plenty of reserve energy to help regenerate roots pruned off during the repot, and their energy reserves are normally highest between Father's day and about Labor Day.

Make sure you delineate between repotting and simply potting up. Repotting is a stopgap measure that temporarily allows a plant to grow a little closer to its genetic potential within the limits of other cultural factors. Unless potting up is done regularly and BEFORE roots get congested to the point the root/soil mass can be lifted from the pot intact, growth and vitality will be negatively affected permanently - even if the plants are planted out. IOW, potting up ensures that the plant cannot grow to its potential.

Repotting, on the other hand, which includes complete or partial bare-rooting and root pruning, ensures the plant WILL have the opportunity to grow to its genetic potential within the limiting effects of other cultural factors. Repotting, with it's accompanying root pruning is the reason bonsai trees can be maintained in perfect health for many generations - hundreds of years; while potting up is one of the more significant reasons many have trouble maintaining a houseplant in good health much beyond the serviceable life of a box of chocolates. ;-)


    Bookmark   October 16, 2011 at 11:08AM
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jenn(SoCal 9/19)

Whoa, my head is spinning. ;-) Thanks Al, I always appreciate your detailed answers.

Sorry for the confusion. I meant that *some* of the plants currently in pots will be planted out in fall (probably early November); I could have avoided confusion by not mentioning those. <:->

I don't understand how potting up ensures a plant cannot reach its full potential. If I buy a plant from the store and grow it in its little pot for a while, it will reach the point where the growth above the pot is proportionately larger than the pot, at which point I'd pot it up (and also re-pot, into gritty mix!) into a pot more proportionate to the size of the plant. Is this sentencing the plant to eventual doom? I don't understand how.

Also - what are the "the limits of other cultural factors"? Do you mean they do well (or not) in spite of limited light, water humidity --- or ???

For now, I'll be more specific about the outdoor plants I want to re-pot. Company is coming in November and I'd like to spruce up the patio a bit with some new pots. We have a few succulents and pelargoniums that have been in terracotta pots for several years (sadly, in the original plain ol' potting mix... poor things). I'd like to repot them into the 5-1-1 or gritty mix before next month. Our weather is still warm (70s, 80s). Can I do that now without setting them back?

Perhaps I should ask the Citrus forum about the best time to plant those out after growing them in a large pot this year, but if you have any advice there I'd appreciate it. :-)


    Bookmark   October 16, 2011 at 12:45PM
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tapla (mid-MI z5b-6a)

When you allow the roots of a plant to get congested to beyond the point where the soil and roots can be lifted from the pot intact, there will be encircling, girdling, j-hooked roots that will eventually grow larger and restrict the movement of water and nutrients to the upper part of the tree. It's not unusual for a home owner to plant out woody material with congested roots, only to see the plant struggle, stagnate, or simply die within a few years due to root issues carried over from the plants days in a nursery pot. I'm sure you've planted bedding plants from cell packs that had extremely congested roots, only to find that at the end of the growing season, if the plant is still viable, that it has grown very little & root growth had been nil. Had the bottom 2/3 of the root mass been ripped off & the rest of the rootage combed out a little, the plant would have grown normally.

IF you pot up before that pivotal point where the roots/soil can be lifted from the pot, you can continue to do so w/o concern for growth vitality, but nurserymen know they need to bump plants up (to a larger pot) BEFORE that occurs or growth/vitality is restricted permanently. I SAY permanently, but that needs a qualifier. The affect on growth/vitality is permanent unless the root congestion is corrected during a repot or before planting out.

Many people feel it's taboo to disturb the roots of plants when repotting or planting out, but that is a myth. Repotting actually stimulates root growth and even promotes blooming in flowering plants.

I guard against guaranteeing that certain practices WILL make a huge difference because of other potentially limiting factors. I try to be as accurate in what I say on the forums as possible, so "within the limits of other cultural factors' is simply a way of saying that "yeah - repotting is a LOT better than potting up, and with all else being equal, repotted plants are going to outperform plants only potted up by a considerable degree - but there are other cultural influences that keep me from being able to promise that if you pot up it guarantees optimal growth." It guarantees the opportunity for optimal growth as long as other factors cooperate, but even if other factors cooperate, only potting up (after that pivotal point) is going to be a limiting issue at some point in the very near future.

I see it all the time in my trees ...... I get too busy & think, "Gee, I'm out of time here. I think that plant can go another year before I need to repot it" only to see that plant decline in the summer months & limp into dormancy. When I repot it in the spring, it pouts for a week or two, then gets its feet under it and takes off, far surpassing it's counterparts that might only have been potted up.

In your climate, I think you can repot the succulents easily and they'll be fine - into the gritty mix, hopefully? I would probably not do a full repot on the Pelargoniums until spring, but I would probably rip the bottom 1/3 of the roots off the root mass & score the sides of the root mass before potting them back into a similarly sized container in a soil similar to what they're in now. In spring, I'd bare-root and repot into the soil of your choice - hopefully one that is durable & drains freely.

Something about potting up vs repotting from one of my threads:

I have spent literally thousands of hours digging around in root-balls of trees (let's allow that trees means any woody plant material with tree-like roots) - tropical/subtropical trees, temperate trees collected from the wild and temperate nursery stock. The wild collected trees are a challenge, usually for their lack of roots close to the trunk, and have stories of their own. The nursery stock is probably the closest examples to what most of your trees are like below the soil line, so I'll offer my thoughts for you to consider or discard as you find fitting.

I've purchased many trees from nurseries that have been containerized for long periods. Our bonsai club, just this summer, invited a visiting artist to conduct a workshop on mugo pines. The nursery (a huge operation) where we have our meetings happened to have purchased several thousand of the mugos somewhere around 10 - 12 years ago and they had been potted-up into continually larger containers ever since. Why relate these uninteresting snippets? In the cases of material that has been progressively potted-up only, large perennial roots occupied nearly the entire volume of the container, plant vitality was in severe decline, and soil in the original root-ball had become so hard that in some cases a chisel was required to remove it.

In plants that are potted-up, rootage becomes entangled. As root diameters increase, portions of roots constrict flow of water and nutrients through other roots, much the same as in the case of girdling or encircling roots on trees grown in-ground. The ratio of fine, feeder roots to more lignified and perennial roots becomes skewed to favor the larger, and practically speaking, useless roots.

Initial symptoms of poor root conditions are progressive diminishing of branch extension and reduced vitality. As rootage becomes continually compressed and restricted, branch extension stops and individual branches might die as water/nutrient translocation is further compromised. Foliage quality may not (important to understand) indicate the tree is struggling until the condition is severe, but if you observe your trees carefully, you will find them increasingly unable to cope with stressful conditions - too much/little water, heat, sun, etc. Trees that are operating under conditions of stress that has progressed to strain, will usually be diagnosed in the end as suffering from attack by insects or other bio-agents while the underlying cause goes unnoticed.

I want to mention that I draw distinct delineation between simply potting up and repotting. Potting up temporarily offers room for fine rootage to grow and do the necessary work of water/nutrient uptake, but these new roots soon lignify, while rootage in the old root mass continues to grow and become increasingly restrictive. The larger and larger containers required for potting-up & the difficulty in handling them also makes us increasingly reluctant to undertake even potting-up, let alone undertake the task of repotting/root-pruning which grows increasingly difficult with each up-potting.

So we are clear on terminology, potting up simply involves moving the plant with its root mass and soil intact, or nearly so, to a larger container and filling in around the root/soil mass with additional soil. Repotting, on the other hand, includes the removal of all or part of the soil and the pruning of roots, with an eye to removing the largest roots, as well as those that would be considered defective. Examples are roots that are dead, those growing back toward the center of the root mass, encircling, girdling or j-hooked roots, and otherwise damaged roots.

I often explain the effects of repotting vs potting up like this:

Let's rate growth/vitality potential on a scale of 1-10, with 10 being the best. We're going to say that trees in containers can only achieve a growth/vitality rating of 9, due to the somewhat limiting effects of container culture. Lets also imagine that for every year a tree goes w/o repotting or potting up, its measure of growth/vitality slips by 1 number, That is to say you pot a tree and the first year it grows at a level of 9, the next year, an 8, the next year a 7. Lets also imagine we're going to go 3 years between repotting or potting up.

Here's what happens to the tree you repot/root prune:
year 1: 9
year 2: 8
year 3: 7
year 1: 9
year 2: 8
year 3: 7
year 1: 9
year 2: 8
year 3: 7
You can see that a full repotting and root pruning returns the plant to its full potential within the limits of other cultural influences for as long as you care to repot/root prune.

Looking now at how woody plants respond to only potting up:
year 1: 9
year 2: 8
year 3: 7
pot up
year 1: 8
year 2: 7
year 3: 6
pot up
year 1: 7
year 2: 6
year 3: 5
pot up
year 1: 6
year 2: 5
year 3: 4
pot up
year 1: 5
year 2: 4
year 3: 3
pot up
year 1: 4
year 2: 3
year 3: 2
pot up
year 1: 3
year 2: 2
year 3: 1

This is a fairly accurate illustration of the influence tight roots have on a woody plant's growth/vitality. You might think of it for a moment in the context of the longevity of bonsai trees vs the life expectancy of most trees grown as houseplants, the difference between 4 years and 400 years, lying primarily in how the roots are treated.

I hope that was helpful.


    Bookmark   October 16, 2011 at 8:47PM
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calistoga_al ca 15 usda 9

Wow I bet that is more than you expected! Where you live Jen, anything you have in a container waiting to go in the ground, NOW is the best time to do that job. Our long cool rainy(we hope)season has, or soon will, start. Preparing the roots as Al has suggested, when you do plant in the ground, is just as important as if you are repotting. The other Al

    Bookmark   October 17, 2011 at 9:00AM
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jenn(SoCal 9/19)

Whoa, Al (tapla) -- that's a whole lotta information to digest.:-) Thank you for a very thorough explanation.

Al (other Al): Would you also re-pot plants now, or do you do that in spring?

What about blueberries? We have 3 plants currently growing in 5-gallon plastic pots; I want to transfer them to larger half-barrels. I'd love to grow them in the ground, but pots are the way to go here in The Land of Alkaline Soil.

    Bookmark   October 17, 2011 at 12:15PM
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