Plant parenting graphicPlant parenthood has boomed since the onset of the pandemic, with many people frequenting local plant stores to find companionship during a time of social isolation or even trying their hand at growing produce. New and novice gardeners find themselves doting and caring for these plants only for them to stagnate or even (gasp) die. How can we prevent untimely death in our plants and encourage growth?

The roots of many plant woes—quite literally—stems from the soil that houses your plant. Luckily, UW Environment houses many soil experts, including plant experts from the UW Botanic Gardens, to help you grow the most luscious, healthy and sustainable garden possible. 

Soil health is one of the biggest keys to growing healthy plants. But in order to nurture healthy soils, we first need to understand what soil is. Many people think of soil as an annoyance to sweep away when dirt enters their homes, when in actuality it is a complex mix of once-living, living and nonliving things—all critical components of healthy, fertile soil.

“Minerals are the least mysterious part of soils—these are the nonliving things. Organic matter is the once-living thing, and this is what makes healthy soil dark brown to black in color. Lastly, the living things aren’t visible and are either underground, scurrying away from you or are microbial and therefore too small to see,” says Earth and Space Sciences Professor David Montgomery. “The importance of the microbes are the least recognized, but they consume organic matter and metabolize it, which in turn benefits the plants. These three elements make for a strong and active symbioses between plant and soil.”

Think of your plants and garden as a living ecosystem. For soil to be able to function in this ecosystem, it needs to be healthy and of good quality. Soil health allows for it to self-regulate, while soil quality is its ability to perform its role within the ecosystem. School of Environmental and Forest Sciences Assistant Professor Brittany Johnson stresses, “soil is wildly important in nearly every process within an ecosystem so maintaining both health and quality is essential. Soil governs water supply and quality, provides 15 out of the 18 elements needed for plant growth and much more. A good soil can do all of these things and more.”

Now that we have a better understanding of what soil is and the importance of healthy soils, let’s dig into ways to build and maintain healthy soils.

Outdoor plants

Plant parenting graphicBefore you fill your garden immediately, UW Botanic Gardens’ Raymond Larson advises patience and suggests observing the garden for a year before making huge changes. Observe how plants react at different times of day and through the seasons: where is the sun at different times of the year? How much light is each area getting? Which one of your neighbors’ plants are thriving and which ones are hanging on for dear life? Larson also suggests “window shopping” when going on walks in the neighborhood, on campus, and at the Arboretum or Center for Urban Horticulture to see which plants are appealing to you and what works best for the region you’re in. 

Once you have a list of plants in mind, test the soil. Dig a hole in the ground and fill it with a bucket of water to see how quickly it drains—if the water absorbs within an hour then move on to planting your plant. Larson and Montgomery both advise working with the soil that is already there, no need to till the soil. In fact, Montgomery advises to only minimally disturb the soil—if at all. After you confirm that the soil is well-draining, dig a hole that uses as much native soil as possible and make sure the hole is big enough to leave space for roots to grow. Drainage is key here, we don’t want roots to suffocate or suffer from root rot. More specifically, Johnson recommends maintaining about 50 percent of the volume as pore space for air and water and for relatively high organic matter levels—5 percent or higher. Knowing how well your soil drains will dictate how much water to give your plants, as well as the frequency of watering. The Miller Library at UW Botanic Gardens provides a lot of great online resources, including a gardener answer knowledge base with more information on soil and to see what kind of soil you have. 

After your plants are in their permanent homes, mulch the soil around your plants to keep weeds at bay (bonus: mulch also is great at holding in water). Be generous with your mulch: Larson advises at least one inch of mulch to inhibit weed growth. 

Plants attacked by common pests can also be protected by natural methods, according to Johnson. Lure in birds and beneficial bugs like lady beetles—also known as lady bugs—to help do your work for you through strategic planting. Lots of plants attract beneficial insects (like mint) or repel insects (like onions), so by planting them alongside more vulnerable plants you can keep harmful pests under control. Alternatively, you can plant something known to attract aphids (like nasturtium) away from your other plants and just treat the one plant. Treatment is a simple mixture of one tablespoon of Castile soap in one quart of water, or add a few drops of essential oils like peppermint for an even more effective mix. This will only affect soft-bodied insects and will not harm any birds, bees or hard-bodied insects like lady beetles.

The last piece of the outdoor garden puzzle is fertilizing your soil. Store-bought chemical fertilizers are labelled with three numbers representing the ratio of nitrogen-phosphorous-potassium (N-P-K). Of course, starting with soil that has plenty of organic matter and lots of space for roots, air and water will provide a great base for your plants. At home, we can make our own fertilizers using lawn clippings, dropped leaves and flowers, veggie scraps and egg shells, while avoiding any fats. Let the compost sit, turn it over often and reap the benefits of homemade compost while cutting down on food waste—a win-win. Montgomery credits his wife Anne Bikle in what he calls the “organic matter crusade” turning unhealthy soil to healthy soil through using compost and mulch to both suppress weeds and feed soil life. In one planting bed with bad weed problems she laid down clean cardboard boxes to control weed growth and added an additional 6 inches of mulch on top of that. Then she dug a hole through the cardboard and mulch to allow for desired plants to get established. An added benefit to this method is that the soil’s organic matter will increase over time, and pull carbon from the sky into the soil.

Indoor plants

Plant parenting graphicMany of the same concepts for outdoor plants can be brought indoors for houseplants, but on a much smaller scale. The same compost can be used for outdoor and indoor plants, and the same treatment can be used to treat pests. 

When bringing plants home from nurseries, they have likely been in the nursery pots for a long time with roots that are compressed and kinked, and the plants are probably on a watering schedule that is more frequent. It is important to switch out the pot to allow for the roots to spread out and breathe. Drainage is the name of the game for houseplants, so look for soil mixes that are well draining. When in doubt, look for a soil mix that promotes air and water flow—made of bark, moss, compost, sand and vermiculite. Try to avoid wet, heavy bags as they could be harboring mold or harmful material and are denser which won’t allow for water, air and roots to move freely. Cacti and other succulents will require a sandy soil that drains well, while orchids prefer almost no mineral matter at all and will be happy with bark and sphagnum moss, according to Johnson. Whatever plant you grow, a light, fluffy mix with lots of organic matter to act as slow-release fertilizer for your plants will work. When plants shed their old leaves, they are trying to feed their roots and the microbes within soil convert the dead leaves into fuel the plant can take up.

When it comes time to move your plants into a bigger pot, don’t throw away that soil! “Soil doesn’t go bad, it just gets sad,” says Johnson. “As long as you are not observing any evidence of harmful molds or other diseases, there is no reason why you cannot reuse the soil.”

Incorporate some compost into the old soil, mix it around and the soil is ready for life with another plant. 

If your first plant (or 5, or 10) don’t make it, don’t take it personally. Through this process of trial and error, we can all eventually learn what each plant likes and dislikes and what it takes to build a healthy foundation for plants to thrive.

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