Feed me!
| 23:23 UK time, Tuesday, 23 June 2009
A question that's cropped up a few times lately at Dig In events is what, and how much, to feed plants? Anyone who's ever looked sadly upon a sorry, stunted, yellow specimen will know that the little leafy darlings need nutrition if they're ever going to flourish. And that's where we can help.
Plants don't eat the soil - obviously, as it's still there after they've gone. Instead, they build themselves out of light, air and water. But they do need a few minerals to pull off this trick and thats what we feed them, especially if there's not enough in the soil or compost they're growing in.
The three minerals all plants absolutely rely on are nitrogen, phosporus and potassium (represented with the symbols N, P and K). Plants suffer in various ways if they don't have enough of these - not enough nitrogen leaves them short and yellowed, too little phosphorus and they'll go purplish and shrunken, and if they refuse to flower or grow fruit, they could well be in need of potassium.
These three are the ingredients of most off-the-shelf plant foods like Growmore and Tomorite, so using any of those will usually help. Don't overfeed though, it can be just as bad - make sure you follow the instructions on the bottle or packet.
This type of plant food is made using industrial chemical processes, so if you've decided to garden organically, you'll want to avoid them. There's plenty of organic options, like blood, fish and bone mixtures (best avoided if you have a dog!), pelleted manure - or just regular old manure. Make sure anything you put on your plants has had a chance to rot down, otherwise it could be too rich and "scorch" your plants - that is, give them a sort of chemical burn.
If you fancy making your own plant food, there's lots of recipes for organic fertilisers out there - try the Garden Organic website for starters. One of my favourites is comfrey tea, effective but very, very smelly. To make it, put five good handfuls of cut up comfrey (pictured to the left) in a tub, and add ten litres of water. After a month, it'll pong of toilets and death, but will be a ready-to-use liquid feed to boost up your plants. Enjoy!
If you've got a special fertiliser recipe, or have advice or a question about feeding plants, let us know by adding a comment below.
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Comments
I've got a question for you Ann, about re-using old soil from pots. I've had salad leaves growing in fairly small pots of garden centre bought compost, and when they've finished, I've been re-using the same soil to sow the next lot of seeds. Is this ok as long as I keep feeding them, or should I change it each time? Also, when everything I've grown in pots is finished, can I just tip the soil from those pots onto my vegetable patch in the garden, or is it better to throw it away/add it to the compost heap? Thanks for your advice.
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That's an interesting question. I saw Alys Fowler talking about just this at Gardeners' World Live, and she keeps on using the same compost in containers year after year, so there's no reason why not. There's one restriction on that - DON'T RE-USE COMPOST IF THE PLANTS GROWN IN IT HAVE SUFFERED FROM ANY DISEASE.
Alys was very clear that you really need to start off with good compost to begin with, and obviously you do have to keep feeding. As you're doing that, it should be fine, though make sure you keep the nutrients balanced.
Using organic sources like blood, fish and bone, seaweed or comfrey liquid manure or a bit of good ordinary animal manure will help with that by adding phosphorous and the less common nutrients (elements like sulphur, calcium, magnesium, zinc, molybdenum and a few more) that aren't included in so many of the commercial feeds, but are needed in very small amounts.
You might also find that the structure of the compost gets a bit rubbish after a few years as the organic material in it is broken down. Again, a nice bit of manure, or top-dressing (i.e, just putting a layer on the top) with more compost will help. A final trick is planting a green manure - plants that help build up organic material and maybe also add nitrogen - in the container when you're not growing a crop. Some commonly used ones, easily available from seed sellers or garden centres, use buckwheat, ryegrass, phacelia, clover, trefoil and tares, just sprinkle them over, then cut and dig in to the compost a few weeks before you want to plant something else.
Spent compost isn't really meant to be added to compost heaps - I've never found it does any harm, but I suppose it doesn't do much to encourage the various bacteria and fungi that actually break down stuff to compost as there's nothing left for them to eat in it.
Putting it on your soil is a good idea, as even though it won't have many nutrients left, it'll help improve the texture, and add organic material. That'll help with holding onto water on sandy soils, and breaking down heavy clay-ey soils. But again, if there's any risk of disease, just get rid of it. Give it to your council, in their greenwaste bin if they provide one. They'll take it away and compost it in a huge heap that should get so hot it'll kill any diseases lurking in it.
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