Re-potting Rhododendron recurvoides and other south east asian beauties

[Corrado & Rina]

Dear all,

I grow few Rhododendron in pots, all botanic species and all not too large, including recurvoides.

I was wondering when the members of the forum that are more experienced than me re pot them: I received suggestions recently from professionals in the field that this time of the year (late Autumn to early Winter) may be the best time for re potting.

A since we are here, what compost do you prefer to use? I am thinking of moving mine to 2 parts of Melcourt Grownbark Pine + 1 part of Melcourt Propagating Bark, it should ensure drainage, moisture retention and very low PH.

Regards

Corrado

[johnralphcarpenter]

I have lots of Rhodos in pots; some large, some small, some very hardy, some not so. I don't repot mine, though I suppose I would if they really outgrew the pot - but I use large pots. I plant them in a free-draining mix or roughly  1/3 JI ericaceous compost, 1/3 orchid mix and 1/3 sharp grit. Vireyas I pot in 100% orchid mix. See Orchid Mix on this page: http://www.ratcliffeorchids.co.uk/Pages/trial.aspx. I also treat with Provado vine weevil killer annually. I prefer to buy bare rooted so they get potted when the nursery ships them in late autumn or early winter, but if I buy any in pots I try to pot them on immediately

[Corrado & Rina]

I have lots of Rhodos in pots; some large, some small, some very hardy, some not so. I don't repot mine, though I suppose I would if they really outgrew the pot - but I use large pots. I plant them in a free-draining mix or roughly  1/3 JI ericaceous compost, 1/3 orchid mix and 1/3 sharp grit. Vireyas I pot in 100% orchid mix. See Orchid Mix on this page: http://www.ratcliffeorchids.co.uk/Pages/trial.aspx. I also treat with Provado vine weevil killer annually. I prefer to buy bare rooted so they get potted when the nursery ships them in late autumn or early winter, but if I buy any in pots I try to pot them on immediately

Thanks John!

Two questions:
1) Is your water acidic then, if you never need to report them?
2) How do you deal with compost decomposing and becoming less and less free draining?

PS: an you post some pictures or your collection, and maybe a list of your plants? I have just started by quickly becoming addicted. What are your favorite nurseries for bare roots plants?

Regards

Corrado

[Robert]

Corrado,

Here in hot California, the organic material in our potting mix breaks down very quickly. In 3 years a 01 a gallon pot will need repotting as the organic material is more or less mush or if it is a fasting growing rhododendron it will be too large for the pot. In larger containers I can get away with a longer period between repotting. Part of this is due to the use of coarse lava rock in the planting mix. The Rhododendrons seem to love this in the planting mix and grow extremely well.

I never repot seedlings until spring or mid summer. Too much fertilizer will kill them very easily. This is what works for me with our climatic conditions.

[johnw]

Due to our extreme wet weather we must be very careful here not to overpot.  If over-potted the real trouble starts when the warm weather arrives - anything over 24c or sun shining on black pots, night temps between 15-20c too can wreak havoc with roots in saturated mixes.  Jens Birck first pointed out to me that rhodo roots grow when soil temps are cool - spring, autumn and in winter for those blessed with unfrozen ground. Having grown rhodos for decades I had no idea root growth was so extensive in late August on!

I repot in August as a rule when it is dry and I can control the watering, those pots are moved under cover if rains are due and the pots have been recently watered. When my partner worked alongside Jens Nielsen pricking out rhodo seedlings he was astounded that he did not immediately water those bare-root tiny seedlings - sometimes a spritz of mist but he'd always wait a few days before using the Haws and then very gingerly.

Lots of coarse bark, pumice, oak leaves and perlite (gypsum, a pinch of slow release and superphos) in the mix along with a tiny amount of topsoil for cat-ion. If we overdo the soil phytophthora will surely strike.

Our rain is acid, our soils are extremely acid but in summer the water coimmission laces our tap water with lime and pH can soar to 8.4.  Once in a while we'll toss a bit of gypsum at the pots to rectify any chlorosis but that has been minimal.   Our mix breaks down very quickly and when the texture deteriorates we can make zero watering mistakes or then phytophthora is guaranteed in late June, July and August. Bottom line the mix must always be an airy one in this part of the world.  I should say I am on the fog bound coast, friends in the interior casn have a slightly heavier mix, however they have problems with Madennias and vireyas in that mix when the rains do occur or with watering slip ups.   

Perhaps Jens will chime in.

Oh vieryas and madds - more bark and lots of pumice, very much less soil if any.

johnw - 0c, grey

[johnralphcarpenter]

Thanks John!

Two questions:
1) Is your water acidic then, if you never need to report them?
2) How do you deal with compost decomposing and becoming less and less free draining?

PS: an you post some pictures or your collection, and maybe a list of your plants? I have just started by quickly becoming addicted. What are your favorite nurseries for bare roots plants?

Regards

Corrado

Lots more advice offered I see. Here we don't have the climatic extremes of California or Nova Scotia;  never too hot or cold - water is slightly alkaline but they don't seem to mind and I feed with Empathy Ericaceous seaweed fertilizer - http://www.rootgrow.co.uk/seaweed-products.html. And we get plenty of rain.

Compost does break down of course but the grit doesn't. My favourite nursery has to be Glendoick - http://www.glendoick.com/.

Having said all that I probably should repot more often, but the plants are healthy and flower well.

[johnw]

Corrado - Jens Birck kindly sent along some of his photos.

#1  Very healthy rhodo seedlings in just the right open mix.

#2 Seedlings have progressed and hardened a bit a a perfect moment to divide them.

#3 As the roots are not congested to transplant one needs simply to pry them apart.

#4 A familiar sight! Completely pot bound the rhodo becomes very difficult to water but once soaked the mix at this point holds little if any air.   Intervention was too late, before transplanting to a new mix one should gotten rid of half that root system either by tearing or mangling or by cutting pie-shaped wedges out of that rootball.  Following that one should then neither overpot nor over-water until the roots have rebounded.  Due to their hair-like roots some novices are afraid to shake up a rhodo's root system, hence the lack of a plant in this pot - RIP.

johnw - +2c & grey

[Corrado & Rina]

Dear all,

You are extremely helpful, and thanks for the very useful pictures from Jens (and now I am tempted to start reproducing from seeds).

The problem I am experiencing is that the weather this year has been abominable: yesterday 14C, a week ago -2C, warm and wet westerly wind at very high speed alternates with days so wet that that frogs are still going around the garden and have not yet hibernated.  These conditions are not at all usual at this time of the year, but they are becoming more and more common.

The weather has been and is such that the compost in the pots deteriorates extremely quickly, and has become mushy, and I am concerned about the lack drainage and oxygen causing phytophtora. For that reason, I was actually thinking of re-potting as soon as possible, into a more aerated and open compost. Do you think I am doing the right thing?

Concerning over potting, how would you define it? If the compost is well aerated and open, would re potting in a 4 cm larger diameter (increase of 2 cm by each side) be alright?

Concerning watering in these conditions, I imagine that if one had to err,  it would be better to be on the dry side rather than on the too wet side.  What do you all think?

The plants are currently in pots elevated over benches and pallets. Would it be worth moving them and protecting them from the rain?

Finally, how vulnerable are the R. to wind, and what type of wind is worst? Cold, dry, norther easterly wind, or wet, warmish, westerly and southwesterly winds?

Regards

Corrado

[johnw]

I think Ralph will have to take it from here as your conditions are not mine.  Phytophthora rarely strikes here in cool weather though I suppose other root rots can.  Particularly touchy subjects we grow in clay pots.  Here we'd go from a 4 to a 6" pot, an 8 to a 10 etc but it depends on how the root mangling process went and how much root ball was ultimately removed.  Remember new mix in pots should be barely damp to entice the roots to move out of the old ball into the new mix. 

johnw - 0c

[Corrado & Rina]

I think Ralph will have to take it from here as your conditions are not mine.  Phytophthora rarely strikes here in cool weather though I suppose other root rots can.  Particularly touchy subjects we grow in clay pots.  Here we'd go from a 4 to a 6" pot, an 8 to a 10 etc but it depends on how the root mangling process went and how much root ball was ultimately removed.  Remember new mix in pots should be barely damp to entice the roots to move out of the old ball into the new mix. 

johnw - 0c

Thanks John.

The weather conditions we are experiencing are not at all common for this season in this part of the world: it would be normally much colder on average, much more stable and not as wet, hence it is difficult to know what to do.

On the other hand last late spring and early summer, and early autumn were much drier and warmer than usual, and we had to water from the mains, which caused other problems, because the mains' water's pH is an average of 7.4, and acidophiles do not like it too much. I need to strike the right balance between moisture retentive and aerated enough for these new winter conditions.

Would you consider recurvoides a particularly touchy subject? It is the star of our very small collection at the moment ....

I am now trying to add hirsutum (the type species but ideally from the western part of the range), but I am finding it difficult to find.

Regards

Corrado







 

[johnw]

R. recurvoides is certainly not a species that is happy in a pot here in Nova Scotia.  Realize we must bring potted rhodos into a frost-free greenhouse for the winter or with the hardier subjects sink those pots in wood chips in a cold frame sealed tightly with opaque white UV resistent plastic.

johnw  - +1c & grey

[Corrado & Rina]

R. recurvoides is certainly not a species that is happy in a pot here in Nova Scotia.  Realize we must bring potted rhodos into a frost-free greenhouse for the winter or with the hardier subjects sink those pots in wood chips in a cold frame sealed tightly with opaque white UV resistent plastic.

johnw  - +1c & grey

Dear John,

I think you wanted to post in the other thread about Rhododendron recurvoides, is it correct?

 .... is it possible to actually move posts, John,Maggie?

Best,

Corradp

[Steve Garvie]

Thanks John.

.........because the mains' water's pH is an average of 7.4, and acidophiles do not like it too much. I need to strike the right balance between moisture retentive and aerated enough for these new winter conditions.

Would you consider recurvoides a particularly touchy subject? It is the star of our very small collection at the moment ....

I am now trying to add hirsutum (the type species but ideally from the western part of the range), but I am finding it difficult to find.

Regards

Corrado

Try adding 10mls of Cider vinegar to 5L of tapwater -that should drop your pH. The eventual pH is dependent on the hardness of your local water -especially the carbonate hardness. Hardwater areas with high carbonate hardness effectively buffer any drop in pH & so wiil need more vinegar. A cheap pH meter can be purchased online and will prevent any mishaps.

Recurvoides is not difficult but might quickly get a bit big for a container. There are a large number of classy dwarf species that deserve to be grown more widely. For example check out Rh. keskei (the clone Yaku Fairy is a wee beauty), forrestii repens, myrtilloides, hippohaeoides, dendrocharis, calostrotum and uniflorum.

If you fancy a challenge try pumilum, pronum, proteoides, ludlowii, lowndesii and cephalanthum crebreflorum. 

All of these plants have been available somewhere in the UK in the last 12 months.

[johnralphcarpenter]

I think Ralph will have to take it from here as your conditions are not mine.  Phytophthora rarely strikes here in cool weather though I suppose other root rots can.  Particularly touchy subjects we grow in clay pots.  Here we'd go from a 4 to a 6" pot, an 8 to a 10 etc but it depends on how the root mangling process went and how much root ball was ultimately removed.  Remember new mix in pots should be barely damp to entice the roots to move out of the old ball into the new mix. 

johnw - 0c

Just returned to this topic. Perhaps I should make a few things clear: 1, I'm no expert, I just happen to grow a lot of Rhodos in pots! 2. I don't grow R. recurviodes but I do grow some Vireyas and Maddenias; the Vireyas stay in the polytunnel but the Maddenias are outside - they may get covered with fleece if it is exceptionally cold, which is rare here. 3. When I said I didn't repot I was referring to mature shrubs in large pots (some very large). Of course seedlings need potting on as John W has described.

Where in the UK are you? Much depends on your local climate.

[Corrado & Rina]

Just returned to this topic. Perhaps I should make a few things clear: 1, I'm no expert, I just happen to grow a lot of Rhodos in pots! 2. I don't grow R. recurviodes but I do grow some Vireyas and Maddenias; the Vireyas stay in the polytunnel but the Maddenias are outside - they may get covered with fleece if it is exceptionally cold, which is rare here. 3. When I said I didn't repot I was referring to mature shrubs in large pots (some very large). Of course seedlings need potting on as John W has described.

Where in the UK are you? Much depends on your local climate.

Sorry for coming back after a while, but I had missed this answer.

How large is very large? Can you give a rough idea of the size of the plant and the pot?

Also, when you re pot Rhododendrons, do you tend to keep in the narrow like Citrus (only increase a couple of cm each side), or can you already pot them in fairly large pots?

PS: Can you post some pictures of your large Rhododendron in pots?

Best,

Corrado