Water: A propagation area will always be a little messy. Make sure to protect any carpet, hardwood flooring, or other delicate material in the area. Most seeds are planted very shallowly, so use a gentle stream of overhead water or bottom-water your flats. Because of the limited soil volume and shallowness of the containers, transplants dry out very quickly. Check moisture at least once a day, and more frequently in hot, sunny weather. The soil should remain evenly moist until the plants have sprouted. Once plants have emerged, allowing the soil’s surface to dry out a bit between waterings will reduce pest and disease issues.
Containers: Plants can be propagated in open flats, plug trays, soil blocks, or recycled containers such as egg cartons and yogurt cups. If you’re using non-standard containers (meaning anything that wasn’t designed specifically for growing seedlings), make sure to poke drain holes in the bottom. Place several seeds in every cell to make the best use of your limited space, then thin to the healthiest plant once sprouted,. As a general rule, always seed at least 20% more than you plan to use in the garden. This will account for unhealthy seedlings and unforeseen disasters. Potting up seedlings into larger containers, such as 4” pots or gallons, may be necessary for cold sensitive crops like tomatoes and peppers that need to live in the nursery for an extended period.
Soil Media: It’s easiest to propagate in germination mix. Germination mix is a finely screened, lightweight medium. The soil’s small particles make it easy for young seedlings to push up through the mixture without being damaged or trapped under a large piece of bark or other substrate in a standard potting mix. As your plants mature, they’ll require more nutrients than a germination mix can provide, which will require you to move them into the garden or pot them up. If you pot up your young transplants to larger containers, use a nutrient-rich, all-purpose potting soil.
Fertilizer: When plants germinate, they have a small stock of nutrients that enables them to become established. However, once sprouted, plants need quick access to additional nutrients. Because propagation containers are shallow and require frequent watering, nutrients leach more quickly than they do in the garden. Frequent, low doses of soluble fertilizer will help your transplants thrive. Keep in mind that over-fertilization can lead to salt buildup or fungal growth, so finding the right dosage and fertilizing schedule is imperative.
Pest and Disease Control: An invasion of insect pests is a real possibility when growing transplants in your home. Keeping your space clean and well ventilated will reduce or eliminate problems. If pests arise, temporarily move the plants outside (weather permitting) and wipe down all surfaces with with alcohol, bleach, or hydrogen peroxide. Sticky traps will help keep persistent insect populations under control. Once plants have sprouted, allow the soil surface to dry out between waterings, this will reduce insect breeding and fungal growth.
Labeling: Label your trays! The importance of plant labeling can’t be overstated. It’s often virtually impossible to distinguish among different varieties of a crop when plants are young. When seeding a entire flat with a single variety, use at least two tags (in case one falls out). When seeding multiple varieties together in a flat, place a tag in each row or each individual cell. The tags can then move with the plants directly into the garden.
If home propagation sounds like your cup of tea, this is a great time to begin building out your home nursery. Allow yourself three or four weeks for ordering supplies and setting up your space, and you’ll be ready to go in early March when it’s time to start this year’s summer crop transplants.