Soluble Salts

Mystery solved!! I'd always wondered what that white build up was on the soil of my house plants, and now I know! It's soluble salts: minerals or fertilizers that are dissolved in water, and are left behind to accumulate after normal evaporation of water.

I used to just take a spoon and mix them back into the soil... oops (don't do that!!). Instead you should scoop the whitish and yellowish film off the top of the soil and discard it. Soluble salts that are present in the soil in concentrations that are too high can damage the plant.

Here's some info:

• Salts form a yellow or white crust at the top of the soil or at the bottom at the drainage holes.
• They can cause salt toxicity, which can result in reduced growth, brown leaf tips, leaf dropping, wilting, root damage, root rot, reduced water absorption capacity.
• Prevention: when you water, allow the water to run through soil and drip out of the bottom of the pot, but do not let the plant sit in that water. Empty and clean the drip tray (the salts will be reabsorbed back into the plant if it is allowed to soak up previously dripped water).
• Every few months, plants should be leached: pour a lot of water on the soil and let it drain completely. Remove any salt crust layer at the top BEFORE leaching so that this salt is not reintroduced to the soil.
• Salt toxicity happens in house plants because of the low light conditions: lower light results in lower water requirements for the plant, which reduces the opportunity for the excess salt to be leached away or diluted.

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PH Scale (My Version Of)

This chart is a work in progress, and I'm not a botanist or chemist... I put it together as a guide for myself re: my plants and how they are compatible with the soil in my garden based on some of the types of things I compost. There are a few items on there that I don't compost, such as milk, that I've included just for interest.

(If you double click on the chart you'll be able to see a larger version of it.)

I've noticed an interesting thing: I drink a lot of coffee, which is acidic, and I compost all of the grinds and filters. On the other hand, we eat very few eggs (the shells of which contain lime, which can make your soil more alkaline).

I haven't been able to grow lettuce for the past two years, and you'll notice on my chart that lettuce tends to prefer less acidic soil. My strawberry plants, on the other hand, are thriving (they apparently appreciate my morning cups of java ;)

This adds an interesting element to garden bed planning and composting. I could create two compost piles (one for coffee grinds and one without) but that complicates crop rotation (i.e. potatoes). Instead, I think the easiest thing to do at this point is to not compost all of my coffee grinds...

Oh and look where Geraniums are on the scale - they really don't like coffee!! On an impulse one day (before learning about PH) I dumped some cold coffee over the soil of a couple of geranium cuttings I have on my counter. Now they're not so happy. Oops...

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