Each spring, gardeners patiently await planting time! Master Gardener Astrid Muschalla leads us through her thoughts on spring planting and some tips on getting started.

Traditionally, many of us have considered the May long weekend as the start of the gardening season, when we are reasonably sure that the danger of night time frost is behind us. Indeed, there are many tender plants, such as tomatoes, that need warmer temperatures before taking root in their outdoor beds.

Soil Temperature

While we often think of air temperature when deciding when to plant, soil temperature is also an important consideration when deciding when to plant. Seed germination is influenced by soil temperature.  Astrid uses a soil thermometer to take a reading at a depth of 1-3 inches for seed sowing, or 4-6 inches for seedling transplants. It is best to take the temperature in the morning when the soil will be at its coolest.  Readings on three consecutive days can be averaged to find your soil temperature. 

Warming the Soil

To get a head start on planting in the home garden, there are various techniques that can be used to warm the soil. Raised beds for example will warm more rapidly, as will raised or mounded rows. Some gardeners will temporarily cover a section of garden with black or clear plastic sheets which act to increase the temperature of the ground below. Floating row covers, plastic tunnels or cold frames can also moderate soil temperature.

That said, seeds will take longer to germinate in cooler conditions, and there is a risk they may rot in the cool wet environment of spring.  Waiting a little longer will likely result in higher germination rates.  

Minimum temperatures for sowing and germination are provided in the image below:

Planting Tiny Seeds

If you have ever attempted to sow tiny seeds such as carrots you will know that it is not easy to spread them evenly, avoiding over-sowing and thus minimizing the need for thinning tiny sprouts.  Seed tape may be the answer.  Astrid makes her own by using a toothpick to paste each seed on a biodegradable paper strip. Flour and water (2:1 ratio) makes a simple paste, and toilet paper a suitable substrate. The strip is then laid in rows in the garden at the depth indicated on the seed packet.  I’ll be trying this in my own garden this year!

Potatoes

Once the soil temperature consistently exceeds 6C, seed potatoes can go in the ground. These are a great crop to break up the soil in a new bed and can be planted from mid April (depending on local conditions) until mid June. Certified disease free potatoes are generally “chitted” or green sprouted indoors. They are placed on a tray in a cool room with indirect light, causing them to sprout . Several of the strongest shoots are allowed to grow, while others are removed. Once the sprouts are about an inch long, simply dig a hole and pop the potato in. Astrid adds a little mycorrhizal fungi to assist the plant in accessing soil nutrients.  Come summer, digging up and eating your own potatoes is one of many gardening joys!