This chilly weather is certainly dragging on, but if you have good growing conditions for seedlings indoors, it should cheer you up to be starting seeds. I wait until now to sow leeks, onions, celeriac and celery as I have found they grow into plants that are just as productive as ones started earlier in February. You can sow peppers and eggplants now if you haven’t already done so. Start tomatoes too if you have space to move them into larger pots later or if they will be planted in a greenhouse. Tomatoes grow quickly therefore you can wait to start them in mid-March and still have nice-sized plants to set outdoors in mid-May. If you are eager to harvest the earliest possible zucchini, start a couple of seeds in early March, but be prepared to move them into 1 gallon pots after a few weeks to keep them growing until they can be planted out in May. As to when in May that might be, it depends on the weather…and who know at this point? There is no advantage to starting seedlings too early if they have to sit in their pots too long, becoming root-bound while waiting for the soil to warm up. An older, but stressed, plant will never produce as well as a younger, later-sown plant that grew quickly without suffering a check in growth.
To grow healthy seedlings requires bright light, warmth and good soil. During the germination period vegetable seeds don’t need light—just keep them somewhere really warm because optimum germination temperatures are 21-30C [70-86F]. Even peas germinate best at 24C [75F]. Seeds can germinate in cooler conditions, but it takes longer and there is a greater risk of root diseases. Find a warm spot in a kitchen or bathroom for seed trays until they germinate or invest in a seed tray heating mat for this part of the job. As soon as the tiniest green shoot tips poke through, however, take the seedlings off of the heat mat and move them to cooler conditions (18-20C/64-68F) under the brightest possible light. People can usually find a warm place to germinate seeds since light is not necessary, but it can be challenging to provide enough light for plants. Indoor seedlings need very bright light, such as under grow lights or in a sunroom or bay window with sun exposure all day. There is barely enough light to grow vegetable starts on the best south facing windowsill, but you can get away with it for a few weeks if the room is fairly cool. When they don’t have enough light, especially in warm conditions, seedlings grow long, weak stems and lean toward the light. See last month’s message (January 14, 2019) for info on a compact grow light setup using a SunBlaster T5 fluorescent tube available at garden centres and West Coast Seeds. I have been using it to start flower seeds and so far they are doing quite well under this simple light setup.
Seedlings started on windowsills (and even those under grow lights) will be sturdier if you can move them into a cold frame or greenhouse on sunny days (move them back indoors before evening). Take care to ventilate a coldframe or greenhouse enough to keep temperatures from getting much above 21oC [70oF]. When it is warm enough to set them outdoors in direct sunshine for a few hours, the little plants will do even better (continue to bring them indoors at night).
And while I think of it, a note on soil mixes for seedlings: make sure the label on a commercial mix states that it a planting mix with nutrients in it for growing seedlings. Some ‘potting mixes’ do not have available nutrients and are intended for plants grown with regular applications of liquid fertilizer. Seedlings started in such mixes stop growing as soon as they run out of the food stored in the seeds, which is almost immediately for small seeds.
And one more thing: Don’t overwater seedlings. Soak the soil when the seeds are planted and don’t water again until the soil begins to dry slightly. Once seeds have germinated, water them well enough to ensure the soil is moist in the root zone, not just on the soil surface. Ideally, water seedling flats from the bottom by setting them in a sink or larger tray of water. Leave them until the root zone has soaked up water, but not until the soil surface gets soggy. If that is too much trouble, just be cautious about watering from above. If green algae or molds grow on the soil it is a sign that it is being overwatered.
Upcoming events: Saturday March 23. I will be giving two workshops for Russell Nursery: 11:00-12:00: Resilient Gardens in a Changing Climate 2:00-4:00 Protecting and Attracting Beneficial Insects For more information, to register and get directions to the venue.