Updated: Mar 9
Many cool season crops like broccoli, cauliflower, cabbage, and kale should be started indoors rather than seeded directly into the ground in order to protect their sensitive early growth from frost. In this brief guide, I’ll walk you through how to get these spring favorites started so that they’re ready to go once it warms up outside!
Starting Seeds Indoors:
Timing: Timing is everything! Generally, it’s smart to start plants indoors 4-6 weeks before the last frost date, assuming you’re not growing in a greenhouse or high tunnel. In our region, this year’s last frost is expected to occur around the end of April, so you’ll be in good shape if you start your seedlings in early March. Here’s a planting chart courtesy of the University of Kentucky Cooperative Extension Service that you can refer to when making decisions about how far ahead to begin:
Media: Choosing the right media for your seedlings is one of the most important parts of getting your plants started! If you aren’t planning on making your own potting mix, you can pick some up at your local home improvement store, but make sure not to grab a bag of regular potting soil because it’s not fine enough for most seeds to root into. We recommend using Pro-Mix because it contains mycorrhizal fungi, which form symbiotic relationships with plant roots and allow them to better draw nutrients from the soil! After you’ve obtained your potting mix, make sure to wet it so that it has the same amount of moisture as a wrung-out sponge--you want it wet, but not too wet!
Seeding: Carefully read the back of your seed packet to see how deep each seed should be planted. Most seeds can be gently pressed down with your fingers and then covered with a thin layer of media or with a piece of plastic like a humidity dome to ensure good germination. For seeds that need to be planted at a depth of 1 inch or more, make a hole in the media with your finger and insert the seed into the impression before covering it with soil.
Water: It’s all too easy for seedlings to dry out quickly, so make sure to stay on top of watering! Press your finger into the container to gauge how wet the media is. If it doesn’t feel moist, or if your plants look droopy, carefully water the seedlings with a gentle stream from a watering wand or a watering can until the media is saturated. Generally, newly established seedlings should be watered at least twice per day!
Light & Heat: Seeds sprout best at temperatures between 65 and 75°F, so placing trays or containers on a heat mat or on a surface that gets natural bottom heat will help with germination. In terms of light, plants generally need between 6 and 8 hours per day, so make sure your newly filled trays have access to sunlight once they’ve germinated. A sunny window will do just fine, or you can use grow lights if your space doesn’t receive a whole lot of sunlight.
Growing Room: Depending on the size of the plug or container that you initially used, your plants might need to be moved to a larger space after 6 or so weeks. When repotting, be careful not to damage the plants’ delicate leaves and stems when pulling them out of the original container and be sure to add compost and a small amount of liquid fertilizer. You can make your own liquid fertilizer by adding 1-2 tablespoons of 13-0-0 to a gallon of water and mixing it in until it dissolves.
Hardening Off: The final step before transplanting is to acclimate young plants to outside conditions through a process called “hardening off.” This can be done 7-10 days before transplanting by placing trays or containers outside on a nice day in a semi-shaded spot for 3-4 hours to expose the plants to direct solar radiation. During this time, you can also begin to water the plants less in order to prepare them for life in the outside world!