Cruelty to Trees: Pots. Part II Soil and Feet

I wrote about this subject Cruelty to Trees: Pots  and again in a recent article about Salix Kilmarnock  and, as a few people have asked about it, there are a couple of points I'd like to add.

Soil: I'm often asked what soil should be used when putting trees in pots. 

First rule - don't use multi-purpose compost, bought in a bag from the garden centre.  It's too "light": it won't hold the tree firmly in place, and it certainly does not hold water well. If it once dries out, you will really struggle to re-wet the compost. 

Don't use garden soil, it's too heavy and will be full of bugs and - in particular - worms. It will tend to become waterlogged in winter, and although it might seem like a good idea to have living organisms in the pot, worms will tunnel around and create air gaps, which will be detrimental to the roots of the tree. You might think about picking out any worms before you use the soil, but there will, of course, be lots of worm eggs, which you won't spot....

What about home made compost, then? The problem with home-made compost is that it's invariably full of weed seeds: domestic composting simply doesn't get hot enough to kill the seeds. You can still use it: but you must be prepared to weed it, and keep on weeding it.

Best option? Use bought-in topsoil, soil from a loam stack, or bought-in organic matter, ie farmyard manure, which should be pretty much sterile.

Don't add water retaining granules - just use good quality planting material.

Top dress once a year:- this means, gently scrape off the very top layer and top it up with fresh. Add a small fistful of granulated feed, if you have any.

Feed regularly: liquid feed, maybe once a month. Growmore is fine, tomato feed is fine, my personal favourite is Liquid Seaweed: they are all much of a muchness, but I feel that the seaweed is the most natural product, and it certainly works.

Keep the ants out: ants ruin the roots of trees in pots, because they mine and tunnel through the rootball. Air on the small feeder roots will kill them, and eventually kill the tree.  Plus, ants will "farm" aphids, so any aphid infestation will become a major problem if you have ants in your pants - err, sorry, in your pots - because the ants will defend the aphids from all predators.

I have two methods for keeping ants out of pots: firstly, when I am planting the pot, I line the very bottom of the pot with a piece of horticultural fleece before I start adding the compost. Secondly, I put my pots up on feet, which can be lovely decorative ceramic things, or just blocks of wood: even old bricks would do, but they are not particularly pretty to look at. 

These ones - left - are on terracotta feet. Usually, three is sufficient, and it's quite an art, to space them out evenly!

Another reason why I always advise standing pots up on feet, is to prevent the tree rooting through the central hole.

And it helps with drainage in winter... however...

Watering:

The drawback of pots-on-feet is that you have to water them more often.

If the compost dries out, it's really hard to re-wet it: see this article on Hot Weather Watering for details on how to deal with dried out compost in pots. You'll know if  your compost has dried out, because the water will run straight through the pot and out of the bottom.

This is a bad thing.

Not only is the water not staying in the pot, it is washing out what few nutrients remain in the soil, so it must be dealt with. As per the article about Hot Weather Watering, the best way to re-wet a potted plant is to plunge the entire thing underwater. But this can be tricky, if it's a big heavy pot, or if you don't have a sufficiently large bucket. An alternative is to stand the pot on a large "saucer" which can be terracotta, ceramic, or plastic - it really doesn't matter. This will catch the water which runs through, and hold it just below the pot, so that the pot can soak it back up, slowly. 

It's a bit catch-22: in winter, you need the pots up on feet for drainage, to prevent the pots getting waterlogged: this also reduces the risk of frost damage to the pot, where waterlogged soil expands as the water freezes, and bursts the pot.

But in summer, you need them in saucers, to retain the water and prevent them drying out.

What are we to do? (*laughs*)

The answer is, you keep an eye on them. If they start to dry out too much - if we have a spell of very hot and/or windy weather, for example, or if you are going away for a few days - then take them off the feet and put them on saucers. Likewise, if when watering them, you spot that the water is running straight through, then put them on saucers for a few days, until the water stays inside the pot as you add it.

This is not as onerous as it sounds: in many ways, it's nice to have to keep checking on your trees in pots (and other plants in pots, as well) because it gives you the opportunity to look at them, to admire them, to enjoy them.

And I do like people to enjoy their trees!

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