Top dressing for succulents

For the discussion of topics related to the conservation, cultivation, propagation and exhibition of cacti & other succulents.
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Kees
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Re: Top dressing for succulents

Post by Kees »

I have used white sand and expanded clay pebbles.
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ralphrmartin
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Re: Top dressing for succulents

Post by ralphrmartin »

I have quite a collection of Tylecodons, and other winter growing succulents and bulbs (good show of Lachenalia flowers right now). The leaves lose plenty via transpiration anyway, even with top dressing.

As for what I use - I get the smallest granite grit that my local quarry does. (It's actually a bit coarser than I would like, but still works OK). I use it both as a compost ingredient and for top dressing. It has the advantage of being £30 for a builder's bag, or £40 delivered, which is a good deal cheaper than the stuff in garden centres. A lot of that is actually river gravel anyway, which is rounded rather than sharp, and thus supposedly not so good.
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Re: Top dressing for succulents

Post by Herts Mike »

Could I suggest no more than one stones depth of top dressing.
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Kees
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Re: Top dressing for succulents

Post by Kees »

ralphrmartin wrote: Sat Jan 19, 2019 6:02 pm I have quite a collection of Tylecodons, and other winter growing succulents and bulbs (good show of Lachenalia flowers right now). The leaves lose plenty via transpiration anyway, even with top dressing.

As for what I use - I get the smallest granite grit that my local quarry does. (It's actually a bit coarser than I would like, but still works OK). I use it both as a compost ingredient and for top dressing. It has the advantage of being £30 for a builder's bag, or £40 delivered, which is a good deal cheaper than the stuff in garden centres. A lot of that is actually river gravel anyway, which is rounded rather than sharp, and thus supposedly not so good.
Why is rounded not so good?
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Re: Top dressing for succulents

Post by Stuart »

I've used 'Westland Potting Grit', about £4 for a 23kg bag and available at many Garden Centres. I use it both as top-dressing and as 30% of a potting mix. It has the advantage of being much darker when wet, if a plant has root problems it will still have darker grit after others around have dried and show paler grit. I use the same for the collection as well as the nursery plants. It is also useful for Haworthias and Gasterias that I grow in pumice which benefit from a heavier grit top-dressing to keep the top layer of pumice in place. Show plants just don't look as good without top-dressing.

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Re: Top dressing for succulents

Post by topsy »

As someone who has used top dressing on pots for decades, I would like to add that one reason I use a very light coloured, washed aquarium gravel is that it helps to reflect more light onto the plants. Compared with their natural environment, in this country our plants receive much less intense light that they would be used to in habitat. It also helps to keep down weeds and algae. I used rounded aquarium gravel also because it is not sharp as I have had sharper grits dig into the plant bodies in particular Lithops.

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Re: Top dressing for succulents

Post by ralphrmartin »

Why sharp grit, not rounded? Well, that's more when making compost, and I use the same grit for both.

Grit should be coarse, and without sand, as fine particles pack into the spaces between the bigger ones and reduce the air-filled porosity (AFP). High AFP is important to the health of plant roots.

The Scottish Rock Garden Club suggests that sharper particles pack together better, thus potentially reducing AFP, but I am not convinced about that from a geometric point of view. The grit I use has a range of random shapes which means it won't pack very efficiently, and I would have thought a fairly uniform set of spheres would give fairly dense packing. Maybe there is a student project in there somewhere to check this out! This too, ignores the effect of the other materials in the compost.

On the other hand, for the same volume, a rough piece of grit will have a larger surface area than a rounded one, meaning it will hold more water by surface tension.

I'm beginning to wonder myself which is really best and why. Googling doesn't seem to deliver any authoritative information on this point. Maybe someone else is better at Googling than me and can enlighten us all.
Ralph Martin
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Members visiting the Llyn Peninsula are welcome to visit my collection.

Swaps and sales at https://www.rrm.me.uk/Cacti/forsale.php

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Re: Top dressing for succulents

Post by el48tel »

The best voidage is obtained by random sizes; uniform sizes give denser packing arrangements
Endeavouring to grow Aylostera, Echinocereus, Echinopsis, Gymnocalycium, Matucana, Rebutia, and Sulcorebutia. Fallen out of love with Lithops and aggravated by Aeoniums.
Currently being wooed by Haworthia, attempting hybridisation, and enticed by Mesembs.
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Re: Top dressing for succulents

Post by aloedanielo »

All I can add to this is whatever top dressing you use, use one that you already include in your soil mix. Nothing worse than separating out decorative gravel when potting on. :grin:
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Re: Top dressing for succulents

Post by D^L »

el48tel wrote: Sun Jan 20, 2019 10:54 pm The best voidage is obtained by random sizes; uniform sizes give denser packing arrangements
I agree that if you carefully pack spheres ideally then even slightly different sized particles can substantially increase the gaps. But is that so for a mix were it is randomly dumped in? I thought these all turn out about 50/50 grit to air.
If you include notably finer ingredients they fit between the large ones and reduce the volume of air, I think particles less than about 1/3 of the basic diameter start to do that.
Welcome any corrections to my understanding!
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David Lambie
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