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Plants that grow well in an indoor garden

Grow Native: Here are five things to know when starting plants indoors for a spring replant.

Scott Woodbury

January 28, 2021

6 Slides

In sixth grade, I started messing around with plants. The professional name for this is horticulture, although my friend liked to call it “hortitorture.”

That’s more like what I was doing in sixth grade. I chopped plants to pieces to see what would happen. It started in the winter of 1978, when I came across a gardening book sitting around the house. In it were helpful pictures and descriptions of all sorts of ways to propagate plants.

One method showed how to slash a plant stem with a sharp knife, then pin and bury it in soil to stimulate root growth (simple layering) and hopefully a new plant. Another method involved scraping a stem and wrapping the wound with wet peat moss and a plastic bag (air-layering). I also learned how to take stem cuttings by soaking them in willow water, then sticking them in potting soil to stimulate new roots (softwood cuttings).

In one weekend, I tormented every plant in the house. I can’t remember if I asked for permission or forgiveness. Either way, my mom didn’t outwardly mind too much, and even helped me create my first indoor grow light garden, where I experimented with these tortured propagules. It was an eye-opening experience. More than 40 years later, my eyes are still wide open. 

Here are five things to know when setting up a grow light garden:

1. Lighting. Use 4-foot inflorescent lamps with cool-white bulbs suspended on chains above the plants. Lamps on chains allow you to adjust height as plants grow taller. This is important because plants that grow in adequate light are more compact and fit into small spaces. When light is too distant (2 to 3 feet), plant stems elongate, grow thin and flop over. So, keep lights as close to the plants as possible — about 5 to 8 inches works best. This will not burn the leaves or dry out the soil, although keep in mind that gardening indoors can be tricky.

2. Airflow. Airflow is critical to prevent fungal disease and promote stronger stems. Keep an oscillating fan going nonstop, pointed at the plants.

3. Water. You should also mist leaves often with water from a spray bottle in addition to watering the soil with a watering can. Cheap spray bottles work, but higher-quality ones available in garden centers last much longer and have better pump mechanisms. Indoor air in winter is tough on plants, just as it is on skin. That’s why I use bath scrub all winter in the shower and why you should invest in a good spray bottle for your grow light garden.

4. Seeds. Native plants can grow in an indoor light garden from seed. Geraniums and coleus can grow by taking softwood cuttings. Consider collecting seeds on your own property or roadsides. Collected seed must be cleaned and stored dry. I keep small quantities in zipper plastic storage bags, in the fridge or freezer where they will keep for many years.

5. Planting. Pull seed out of the refrigerator when you are ready to begin. If you sow fresh, dry seeds directly into potting soil, only a few species and a small percentage of seedlings (per species) will germinate. Most will not germinate without pre-treatment, but the species that will sprout without treatment include asters and goldenrod, columbine, goats beard, alum root, yarrow, shining bluestar, American bellflower, grasses, rose mallow, buttonbush, wild hydrangea, partridge pea, lance-leaf and star coreopsis, plains coreopsis, blazingstars, Bradbury bee balm, black-eyed Susan, cardinal flower, blue lobelia, gumweed, American aloe, autumn sneezeweed, and sunflowers.

In April, bring plants outside, protecting them from direct wind for the first week. They will need more frequent watering outdoors, especially when temperatures are warm. Then plant outside in the garden or share with others.

Preparing your plants

For the species that won’t germinate, you must pre-treat the seed. Here’s how it’s done.

First, add a pinch of seed to a small zipper plastic storage bag with a small handful of moist (not dripping wet) potting soil and mix well. We use 50% sand mixed with 50% pure peat moss.

Peat moss is acidic and suppresses most, but not all, fungal growth. Place the moistened mix in the refrigerator for at least two months, although three months is better.

This part of the process is called cold-moist stratification. This is where seed is fooled into thinking it spent the winter outdoors. Cold-moist typically happens indoors November through January, but also can happen in spring or summer.

Once a month, check to make sure the seeds don’t dry out. If drying occurs, add a very light sprinkle of water if necessary (not too much). Also, mix the contents using your fingers, without opening the plastic bags. This stirs air back into the peat moss mixture, which also helps prevent fungal growth.

While seed is in stratification, set up your grow lamps. A good place to do this is in front of a south window, to take advantage of natural light. If this isn’t possible, set it up in a basement or another available room. You will need standard electric outlets, extension cords, a grow light kit or cheap inflorescent lamps, an oscillating fan, and a table to support the plants off the floor.

Unfinished basements work well because it’s easy to hang lamps from the exposed rafters and clean up spilled water on concrete floors. Use a table you don’t mind getting dirty and wet.

Find a small watering can with a gentle nozzle, because young seedlings are damaged by vigorous splashing. Use potting or greenhouse soil mixes — rather than topsoil or compost — because they drain well and are porous (soil needs to hold air for healthy root growth).

Any containers will work as long as they are at least 2.5 to 3 inches deep.

Once seedlings are three to four weeks old, begin to use liquid fertilizers weekly — mix 1 tablespoon per gallon of water. When plants are two to three months old, add slow-release fertilizer scratched shallowly into the surface of the potting soil.

This is the process that worked for me. Happy indoor gardening!

Woodbury is a horticulturalist and the curator of the Whitmire Wildflower Garden at Shaw Nature Reserve in Gray Summit, Mo. He also is an adviser to the Missouri Prairie Foundation’s Grow Native! program.

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