Plan Your Best Garden Ever: Testing Soil and Seeds

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Seed packets

Is everyone having as much fun as I am creating a garden plan for this year? There are so many possibilities, and fortunately no big rush yet. While you are working on your plan you can start preparing for your best garden ever by attending to seeds, seed-starting equipment, and the status of your soil.

Start Selecting Seeds

Shall we start with the seed catalogues filling your mailbox? Seed catalogues make great bedtime reading, because while you sleep your brain can consider that new broccoli variety that grabbed your attention. Keep in mind that you need not order all your seeds at once. Each year I make at least three seed orders from three different companies, often at different points in the growing season. Plus, there are seeds to be picked up at retail racks and seed swaps, which are not to be missed.

Testing seed viability
Testing seed viability of onion seeds leftover from previous seasons by germinating them in damp paper towels

You should also inventory what you have, and it’s a good idea to check the germination of seeds more than two years old. Vegetable seeds that tend to be short-lived include corn, onion, lettuce and parsnip, though all seeds lose their mojo over time. See our article on testing seed germination to learn how to tell if old seeds should go in the garden or compost bin.

While you have your seeds out, go ahead and set aside those you might start early under lights. The first seeds to be sown at my house are onions and hardy perennial herbs and flowers, started in January.

Seed flats under grow lights
Fresh seed starting mix is free of pathogens that might infect tender young seedlings

Prepare for Indoor Sowing

Each year I buy a fresh bag of seed starting mix, or make my own potting mix for starting seeds. Leftover bits from last season get mixed into my main supply of potting soil rather than being used for seed starting, because bags that have been open for months may host fungi and bacteria that are unwelcome in small seedling containers.

Should you wish to revive a weathered batch of seed starting mix, place it in a heat-proof pan, cover with aluminium foil, and put it in an oven set to 150°F (65°C) for an hour to kill lurking fungi.

Grow light shelving
Clean your grow lights and replace weak bulbs before you start sowing seeds

Vegetable, herb and flower seedlings grown indoors require supplemental light, and I often find bulbs that need replacing when I plug in my grow lights. Wiping dust from bulbs also can improve their performance. Indeed, after being stored in the basement for six months, my entire grow light shelf needs a good wiping down with warm, soapy water.

Soil Testing

You don’t need to wait for spring to test the soil in your garden to learn more about its nutrient levels and pH (the measure of acidity or alkalinity, which affects how well plants can take up other nutrients). Last year I thought that the newest beds in my garden were too acidic, and even bought a bag of lime to raise the soil pH. Then I did a soil test which revealed that several years of applying wood ashes had already moved the pH close to a perfect 6.5. Had I forged ahead with my plan to lime, I would have created a new problem.

Testing soil pH
A soil test kit shows notable differences in the phosphorus levels and pH in two areas of Barbara's garden

In the US, you can get a soil test done through your state extension service free or at very low cost, but doing your own soil testing makes it easier to study the soil in different parts of your garden. Mail-in soil test kits are widely available, but I like at-home soil test kits because you can test individual beds and get immediate results. The soil samples used in at-home tests must be powder dry, so there is a short wait between taking samples (in labelled containers) and running tests for pH and the three major nutrients – nitrogen, phosphorus and potassium.

If you regularly amend your soil with compost like I do, soil testing will likely reveal that phosphorus and potassium are in good supply, but that nitrogen levels can use a boost. Nitrogen, the growth nutrient, is provided by manures, plant meals and fertilisers, but then it is taken up by plants or washed away by rain. But here’s the good news: after many seasons of at-home soil testing, I have learned that my oldest beds, which are rich in stable organic matter, do a good job of retaining residual nitrogen, while newer beds require more fertiliser to keep my crops happy. Test results guide me in creating my planting plan and deciding how much organic fertiliser to use without overdoing things and contributing to water pollution.

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