Seedling care
As anyone who has ever grown plants from seed knows, getting seeds to germinate is only half the battle. Following that, there are weeks or months of keeping the little seedlings alive and well until they can go into the garden. Producing a strong seedling, ready to transplant, means earlier flowering and resilient mature plants. Here is how I grow on my seedlings to make sure I have a productive season full of blooms.
Light levels After germination, your little plants will need at least 12 hours of light a day to grow properly. We use LED tubes to ensure the plants get strong light that doesn’t burn up our electricity bill. I keep the lights 2” above the seedlings at all times and adjust as they grow. LEDs have the added benefit of not giving off heat when working so they can be kept close to young seedlings without worrying about damaging your plants. Positioning the lights too far above your seedlings will cause them to stretch and grow weak stems that will be easily damaged outdoors. It is also a waste of electricity as the farther away your lights are, the more light is directed beyond your plant trays. I also rotate my trays regularly to encourage even growth under the lights.
Growing on cool If you’ve used a heating mat or a humidity dome to sprout your seeds, make sure to move your seedlings off the mat to a cooler location and to remove the humidity dome once you achieve good germ or see no more seeds sprouting. Room temperature or cooler is best for young seedlings as you want to mimic the conditions they will be transplanted into as much as possible. If possible, keep your plants cooler at night than in the daytime, to also prepare them for the outdoors.
Keep air circulating Keep a fan blowing on your seedlings during the day to encourage strong stems and prevent moisture or disease from causing problems. As my seedlings grow, I increase the power of the fan to keep them growing sturdy leaves and stems. If you have a large number of seedlings like me, they can really add to the humidity of a room so you need to monitor this carefully. I know when I plant my seedlings outside, they will be going to a low humidity environment because Alberta has a dry climate. I have a meter in my basement monitoring humidity and if it gets above 30%, I open windows to move air and lower the moisture content. I don’t want my seedlings to go into shock as they are transplanted from a tropical forest to an Alberta desert!
Feed, feed, feed The soil less potting media you started your seeds in will not sustain your seedlings as they grow. They need nutrients in the form of plant food. Any plant food will do. I prefer to use organically certified liquid fish and kelp food or an all purpose organic liquid fertilizer. Once my seedlings have a set of true leaves (the leaves that appear after the first leaves, the cotyledons), I begin feeding them with a dilute fertilizer. I feed every time I water to simplify and avoid having to remember when I last fertilized. As the plants grow I increase the strength of the fertilizer to water ratio to keep up with the growing plants.
Bumping up Depending on when you started your seedlings, they may outgrow their soil blocks or trays before you can plant them outside in the garden. If your seedlings start to fill they tray and their leaves begin touching each other, it’s time to bump them into a bigger soil block or container to give them the best chance to grow on stocky and healthy. Crowded plants become tall, spindly plants as they attempt to compete for the light by racing ahead of their neighbours. These same spindly plants will be a nightmare to transplant as their stems will most likely break or suffer wind damage, setting back the growth of the plant. Better the spend the time potting them on to a bigger container and keeping them healthy.
Hardening off Before your seedlings can go into the ground, they need to spend a week or so acclimatizing to the outdoors. This is an important step to ensure all your hard work of nurturing your little plants isn’t wasted by having them die of transplant shock. You must gradually expose them to the elements to prevent this. Give them a sheltered spot away from strong wind and full sun to being with, then gradually increase the sun and exposure as they adapt during the week. Carefully monitor your moisture levels during this time. The strong spring sun can dry trays out in a heartbeat. I have killed my fair share of seedlings by forgetting to water first thing in the morning. Too much wind will also stress and dry out plants. If the forecast is calling for gusty winds, wait to harden off your plants until things improve unless you can provide them with complete shelter. I always try to transplant on a cool, cloudy day, preferably with rain in the forecast, to give my seedlings the best conditions while they set down new roots. A bright sunny day feels like a good time to transplant but it can send your little plants into shock. At least wait until the evening to transplant if there are no cloudy days ahead. Then the plants get a cool night to adapt.
As I write this, we are only a few weeks away from our last frost and my house is starting to strain at the seams with plants. I’ve been watering and feeding some of these plants since January and I’m ready for them to get out of my basement! I will begin hardening them off as soon as the nights stop dipping below freezing and then it will be out to the garden. Seeing plants that I started from tiny seeds grow on and bloom in my garden never gets old. Here’s to bountiful gardens this summer!