Perlite

I was wondering if Perlite is useful as a top layer on a potted rose, for protecting it from winter cold? As Perlite is an expanded rock, with a lot of air bubbles inside it, I am wondering if the air traps and insulates heat just as air in clothes does for us?

My new rose is planted in a very large plastic pot, I had mixed my 40 litre bag of potting compost with 10 litres of coconut coir and some Perlite, then after planting I topped the pot up with an inch or so of a mixture of potting compost and Perlite that contained more Perlite than compost, which I had mixed in a bucket.

I did use Mycorrhizal fungus in the planting hole.

 

Hi,

What Type of Rose is it and what is its name and what is the size of the pot ?

Assuming its outside then Perlite as a topping will probably just blow away in the first strong wind.

To us it sounds rather an excessive compost mix for a Rose, good old garden soil is what ours get.

Unless its some very special form of tender Rose then most are frost hardy, though if its just been planted probably worth keeping the pot wrapped in some bubble film or similar to stop the roots being frozen and if very frosty placing some breathable material like hessian or horticultural fleece around the stems.

Are you in a very cold part of the country , eg North or South

 

It is 4 degrees Centigrade here right now, and the weather forecast predicts a top temperature of 10 degrees Centigrade tomorrow. I felt cold outside. Not a cold part of the country, South, and we almost never get snow. I am not expecting the temperature to fall below freezing, it rarely does here. It is a huge pot, I will go out and measure it later. The rose is Starlight Symphony, a climber, bare root. I think I have some bubble film that I could wrap the pot with. When I get some more bags of compost I will replace the high Perlite to compost mixture at the very top, if it will just blow away and be of no other use. It is tricky finding bags of compost at the moment, and I was stretching it with Perlite and Coconut Coir to try not to run out.

It is a very sheltered spot without much wind, though Perlite can splash out of pots a bit when it rains heavily. Still, a good idea to replace the top inch with compost as soon as I can.

I am having great difficulty finding sources of bags of compost at the moment.

I was just wondering if the air in Perlite has any insulation benefit?

 

Bare root roses are dormant, there is no shoots or soft growth on the top. A rose, even freshly planted, will take 4°C with no problem. I would only be concerned if you were due have bitterly cold weather with a wind, when taking steps to prevent the pot freezing through would be a good idea. In that case I would stand it in a garage or shed until the worst is past.

 

Thats a lovely looking Climbing Rose and we would be happy to have one in our garden.

We are no rose experts but our feeling is that, assuming your use of the term "potting compost " refers to either a typical bag of peat based compost or one of the non peat modern composts , then your mix with the extra coir and perlite cold mean that its so free draining the rose could dry out too readily.

The RHS recommend for that Rose "Soil: fertile, humus-rich, moist, well-drained soil" to us that means good garden soil mixed with manure or garden compost which should help retain the water.

Think you would be well advised to put a post in the Rose section of the forum to see what the regular rose gurus think of your potting mix, if non of them sees this post.
Better safe than sorry !

Not sure why you are having a problem with buying potting compost, are your local garden centers out of it ?

 

I'm not a fan of perlite, but that's another story.
I dont think I would use it in a potting mix for a rose.
And I dont think you need to worry about insulation.

I'd go for JI no 2 with some peat based or non peat based multipurpose compost added if it seems a bit too heavy and muddy, as it sometimes does, depending on the quality of the soil used to make it.

 

A mixture of 50/50 John innes and multipurpose will be sufficient. With climbers then the bigger the pot the better, I would recommend a pot that is 50 to 60cm in diameter and depth, which would require 125L to 200L of compost to fill.

 

Thanks for replies. I look at the Met Office weather forecasts, which give temperatures and "feels like" temperatures. I suppose the former is what plants experience, and the latter what humans experience?

I need to learn more about the different potting media. I am not sure what John Innes is, but from what I gather from looking online it is some sort of soil based compost.

I assume that Perlite is mainly to keep air in among the compost and stop it compacting, though have read that it provides water too, though not as well as Vermiculite, and that it retains nutrients for the plant.

 

@gks, my pot is 55cm diameter. In total it contains about 50 litres of potting compost, 10 litres of rehydrated Coconut Coir, and a fair bit of Perlite, all mixed well together. And Mycorrhizal fungi around the roots. As somebody said, the Perlite seems to gravitate to the top of the pot, maybe all the rain.

Later on I may have to re-pot the rose in a bigger pot. I am not sure if people usually expect to have to increase the sizes of their rose pots as they go along. Like somebody said, I probably need to ask on the rose forum.

I often wonder where people get these really supersized pots from for growing roses in.

 

I am guessing that the 55cm is the diameter of the top of the planter. But what is the internal diameters of the pot, top, depth and base? Most people say they have a large planter, 50cm or 60cm at the top, it does not necessary mean you have a large pot/planter, certainly depth wise.

Reading through your posts, I doubt you have a decent sized enough pot/planter. I don't understand why you are even considering wrapping the pot with plastic bubble for insulation if your pot has a 55cm dimension.

Is it possible for you to upload an image, my gut feeling is your pot is not big enough.

 

Florus Black Plastic Bell Plant pot (Dia)55cm | DIY at B&Q

It says 40cm high. And it looks to taper quite strongly towards the bottom.

 

They look very similar to one here.

Extra Large 55cm Round Barrel Planter Plastic Plant Pot Flower Planter Black 5016447011993 | eBay

The problem is, there dimensions are external, not internal, which makes a big difference in volume.

Using internal dimensions, a 50cm square planter would need 125 litres of compost. The above links show a pot 55cm in diameter and 40cm in depth but with a capacity of only 45 to 50 litres.

 

I am actively looking for supersized pots for growing roses in, and at some stage I will probably have to repot this rose. So far, this was the biggest I could find.

I have a few more older roses in pots, and two in particular will at some stage need bigger pots, both grown from seed 18 months ago, one is a rugosa (gorgeous golden foliage in autumn) which is currently happy in a 40cm diameter by 40cm height pot but at the end of next summer I will probably find that its roots have filled that pot. Even my Angel Wings (miniature) roses' roots can fill 40cm diameter by 40cm height pots after two years from seed, and start to be less floriferous and vibrant (I cut them back a lot and fed them, and they seem to be recovering. After one year from seed they were covered with flowers and stunning).

I will try googling 50cm square planter. Edit: B&Q do them, but they are out of stock in my area. They were selling them for half price, £25, and may have some left in your area. I just looked and they still have some in other branches in other areas, lucky them.

Hoa Dark grey Concrete effect Fibreclay Square Plant pot (Dia)50cm | DIY at B&Q

Thanks for your advice gks.

 

Most garden centres stock really big containers, but they are, as far as I'm concerned, very very expensive.

I picked up some big pots from a garden centre recycling area a while back.
But obviously they are not ornamental in any way, just big black plastic pots.

 

Gardensuperstore has a good selection of big pots at reasonable prices. They have both utilitarian and decorative ones. I have a couple of decorative ones and the quality is quite impressive- very thick and sturdy.

My outdoors 50cm pots are from Asda, about a fiver each 15 years ago. They are also about 50cm tall and very rounded shape so the bottom area is big. Even with that they fall over when anything taller is in them. Much less than tapering pots though.