Getting a Head Start on the Summer Growing Season

Author: Rob Stuart, Master Gardeners of Ottawa-Carleton; published with permission.

Mid-March in Ottawa is usually the ideal time to start sowing seeds of annual flowers, vegetables, and herbs that you plan to grow this summer. Hopefully, you already have the seeds ready, either saved from last year’s harvest or purchased at a local store or via an online retailer.

Read the Seed Package

Each seed package will contain instructions on when to sow your seeds, relative to the average last frost date in your area, the temperature in which to place your pots, how much soil you should use to cover your seed, as well as approximately how long it will take for them to germinate and start growing. Every package of seed will contain different instructions, depending on the type of seed.

Many vegetable plants are either annuals, such as tomatoes, peppers, and corn, or biennials, such as carrots, beets, and parsnips. They will either grow fruit in their first year (tomatoes, peppers, and corn) or produce edible roots, as is the case with carrots, beets, and parsnips. The fact that they are biennials is not really important to us for the purpose of the harvest, so we treat them as annuals. Generally, perennial vegetables such as asparagus or fruits like raspberries or strawberries take more than one year after sowing before they can be harvested.

Annual flowers such as sweet alyssum, cosmos, or petunias will flower the year they are sown and will die in the fall. Seed can be collected and sown again the next spring to repeat the cycle. Be aware, however, that some of the original plants may have been hybrids, and their offspring may look very different from the parent plant.

Sowing Your Seeds at the Right Temperature

Many gardeners decide to purchase garden-ready bedding plants at nurseries or large box stores. Those who want to start their plants from seed should make a few preparations ahead of time, since sowing and germination are just the start of the care needed.

While you may be able to place your pots of sown seeds on a window sill, it is generally a much too cool environment to get good germination. If they do germinate, you’ll need to turn the pots a quarter turn each day to ensure your seedlings are evenly exposed to light and are growing straight. That requires a lot of care and attention. Additionally, the cool temperatures on a window sill will tend to slow the growth of your plants, which could delay the date you can transplant them into the garden. Some plants, such as cabbage, broccoli, and Brussels sprouts, do like to grow in cooler conditions, but tomatoes, peppers, and eggplants prefer consistently warmer temperatures. Placing your pots in a warm spot in the house, on top of a heat mat, or under grow lights creates optimal conditions for germination.

Growing Requirements and Transplanting

Needless to say, unless you are planning on growing just a few plants, you’ll need an appropriate setup. A tabletop with grow lights above will ensure your plants have warmth and light. Depending on the type of grow lights you plan to use, you may require some type of ‘stand’ on which to insert your lights or ‘suspend’ them from the ceiling. Ideally, your system will allow you to adjust the height of the lights. This way, as the plants grow, you can raise the lights to prevent the burning of the leaves. If you don’t have a large tray on which to place your pots, then you can place individual saucers under each one, which requires more work.

Transplanting into Larger Pots

Your plants will need to be transplanted from the seed pots into individual, larger pots once they reach about 10–15 cm in height. Typically, the first individual pots would be about 7 cm square and about the same depth. Use soilless potting mix, which tends to be disease- and insect-free and is ideally suited to growing healthy young plants. As your plants grow, make sure that they are watered as needed. Usually, it is safe to water when the top 1 cm of soil in each pot is dry, then water thoroughly.

As your plant outgrows its small pot, it is important that you transplant it into a bigger one, no more than an additional 2.5 cm in diameter. A much larger container will create an environment that will stay too wet for too long. The plant will be too small yet to use the water quickly enough, which will likely cause the plant roots to rot.

Fertilizer Choice

With respect to fertilizer, you should use a half-strength water-soluble 20-20-20 fertilizer every couple of weeks once you move your seedlings into their own pots. Depending on the rate of growth and the weather outside, you may need to transplant your plants again. Only do this selectively, as required.

Hardening Off Your Plants

As you get closer to the day when you will put your plants out into the garden, you will need to prepare for this event by hardening off your plants. This means exposing them slowly to outside temperatures and light conditions. You should do this over a period of about two weeks, initially putting your plants out in the shade for a few hours a day. You’ll need to bring them into the house in the evening or whenever the temperature might drop significantly. Make sure you extend the amount of time outside and the amount of sunlight they are exposed to on a daily basis. A couple of hours per day is generally sufficient.

Eventually, you should be able to keep your plants outside through the day and night. Then they will be ready to plant out after the average last frost-free day of the spring. Generally, this is about May 10, but will vary based on whether you live in the city, the suburbs, or the country. Ideally, choose a cloudy day to put out your plants in the garden, water them well, and cover them with a floating row cover to protect them from a late, unexpected frost, if necessary. This is particularly important for your tender plants such as tomatoes, peppers, zucchini, and annual flowers such as impatiens, petunias, begonias, and dahlias.

Always have a Watering Strategy

Water regularly as necessary—at least 2.5cm of water per week—including both rain and irrigation. Apply compost mulch to reduce water evaporation, release nutrients slowly into the soil, and reduce weed germination. With these steps, you’ll be well on your way to a successful summer gardening season.