I’m going to be writing a short series on the importance of, and how to build, healthy soil. Most newbie gardeners don’t see it as a sexy part of gardening – it’s not colorful or pretty but dirty and, sometimes, icky. Because I can geek out over the lovely, rich, dark stuff and become as passionate about it as if it were chocolate, I’m hoping I can change a few minds.
One of the best, if not THE best, pieces of gardening advice I ever received was that before I spent a dollar on a plant, I should spend a dollar on the soil that plant goes into. Now, that came from Austin’s organic gardening guru, John Dromgoole, a man with a highly successful garden centre that sold a plethora of organic soil amendments but it still makes good sense. Soil – my first soil science prof in college always became outraged when any of us newbie landscapers called it ‘dirt’ – is, for most plants, its nutrient system, its physical support system, its home; how healthy that soil is determines how healthy that plant is, how well it can fight off diseases, how drought-tolerant it will be, how quickly it can recover from insect damage, and how delicious its produce will taste.
That point was illustrated for me when I started my lemon basil, peppers, and tomatoes this year. I made a quick run to the big box store for my seed starting mix – my local garden centres not being open for business yet – and was only able to get potting mix. (For the record, there is a difference between seed starting mix and potting soil. Generally, the seed starting mix is fluffier with less, or no, large chunks of wood, and has added fertilizer for seedling growth.) The label on the potting soil bag said it was an “organic mix” of peat moss, compost and perlite, not an ominous sounding combination, although coir is becoming the new hot substitute for peat moss because it’s a far more renewable product but still, I didn’t think I’d have many problems.
But all compost is not created equal and the percentage of perlite in the mix, used for loftiness, was negligible, resulting in a wood-splinter-heavy and dense medium that I wasn’t sure my little seeds would have the strength to break through. More than half of the lemon basil and half of the peppers never did but that could be because the seed is getting old. There’s no excuse for the tomatoes though, since I used fresh seed, and they were extremely slow getting on.
So, disappointed and worried with the results so far, having spent all my dollars on seed and not wanting to jeopardize that investment, I dashed off to the (Edmonton) local gardening guru’s garden centre (now open), and queried them about seed starting mix. Never use it, they said, have you tried these pellet thingamajigs? I explained that I like to make my own newspaper pots for starting my seeds in and asked them what they use in the greenhouse to start seeds. I was shown a lovely fluffy mixture that they market as potting soil, a blend of sphagnum moss, perlite, dolomitic lime, trace micronutrients, soil-wetting agents, and slow-release fertilizer (enough for 3 months).
I promptly bought 40 litres, planted more basil, peppers, and tomatoes, and nervously watched the results.
No discernible difference between the tomatoes started on March 17 and those started on March 25.
The seedlings had no problems pushing through the medium, resulting in a much faster emergence, probably by about a week! They’re green and healthy looking, although I have been feeding them a half-strength naturally sourced liquid fertilizer, because I’m not sure what type of or in what proportion, the nutrients are present in the potting mix.
This uncertainty about what’s in a bag of potting mix has me frustrated! And if I, a professional gardener, am frustrated, I can’t imagine how a less experienced gardener feels, so here’s some advice based on what I’ve learned to date…
- Don’t purchase potting mix or any kind of soil or compost mix from a big box store unless you’ve used it in the past and been happy with the results. I purchased my potting mix from a big boxer because I thought it was my only option but, had I waited until my local garden centre opened, I wouldn’t have wasted my money – live and learn.
- Read labels. Personally, I think soil, compost, potting mix, etc. should all have a list of ingredients – and even the source of those ingredients but, since we can’t even get source labelling on our food, I know I’m dreaming to think we can get it on something we don’t immediately put in our mouths. The label should, at least, tell you what you can expect to see in the bag but even that’s not a guarantee. For example, it has consistently been my experience that the cheaper the compost, the more wood chunks are in it – you don’t want a lot of wood in your compost since it throws off the carbon/nitrogen balance. If there’s no label, as is the case for bulk soil and amendments, or you think the label doesn’t provide enough information…
- Ask questions. Ask if they can open a bag and show you what you’d be buying. Tell the staff what you’re using the mix for and ask if it’s appropriate. And if they can’t tell you what is in the stuff you’ll be growing your food in, walk away.
What we grow our plants in is important. A good potting mix allows seeds to germinate easily, doesn’t dry out too quickly, or compress when watered and remain soggy. Potting mix isn’t, technically, soil, since it is composed of soilless ingredients. But it’s the first growing medium that many of our cultivated plants first encounter - get it right and you’ll have less problems down the road.