Indoor Plants | Garden Club of Irvington

By Judith Gouraige, Ph.D.

Until we heard Judith’s talk, 99% of us did not know that 50% of the water on earth is produced by oceanic plankton.

Garden Club member Judith Gouraige has been a leader in science education in New York City and Westchester Country schools for more than 20 years. Her roles have included implementing AP programs and working with administrators, teacher leaders, and classroom teachers to plan strong 9–12 science programs. She has an M.S. in Educational Leadership and Administration from the College of New Rochelle and a Ph.D. in Science Education from Stony Brook University.

She recently spoke to Garden Club members and guests on the subjects of soil and water, emphasizing that for optimum plant health water and soil can’t be separated (and making many of us wish she’d been our high school science teacher.) The talk included a “not too geeky” summary of the effects of global warming: More water is in the atmosphere because it’s hotter, and we’re having more and stronger storms that cause floods. And she recommended that we collect and recycle rainwater.

Following are Judith’s practical points related to plants’ soil and water needs to keep in mind, especially now that winter is here and most plants we’re taking care of are in pots, living indoors in less than ideal — too dry — environments.

“Water is involved in every cell,” Judith reminded club members and guests during her talk at the O’Hara Nature Center. “97% of the earth is covered with water.”

WATER

Water is the essential nutrient for plants and comprises up to 95% of a plant’s tissue. It’s required for a seed to sprout. As the plant grows, water carries nutrients throughout the plant. The roots reach toward water sources and pull the water toward the stem and leaves.
Water is necessary for photosynthesis. During this process, plants use carbon dioxide from the air and hydrogen from the water, absorbed through their roots, to make their food, glucose. Oxygen is released as a byproduct.
Water is responsible for cell structural support in many plants, creating a constant pressure on cell walls called turgor, which makes the plant flexible yet strong, and allows it to bend in the wind or move its leaves toward the sun to maximize photosynthesis.
Winter is the time for dormancy, and therefore less watering (if any) is needed for outdoor plants. Indoor plants require watering at least weekly. If you have forced-air heating, thus very low indoor humidity, use a hand-held water meter to check the soil.

Attendees were given worksheets with the formulae for water, the physical characteristics, density, and amounts of water in the atmosphere, on the earth, in the body.

SOIL

Soil is the substrate in which plants grow and obtain nutrients. Plant roots reach into soil pores and collect nutrients that are held in the soil. Bacteria and fungus in the soil break nutrients from mineral and organic sources free, making them water-soluble for plants to use.
Plant roots create smaller pores in the soil, which help serve as water and air channels in the soil. A healthy soil is about 50% solids (minerals and organic material). The rest is pore space for air and water.
Plants need nutrients. Essential ones are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Carbon, hydrogen, and oxygen are largely absorbed via the air and water. Nitrogen, phosphorus, and potassium (NPK) are the main components of fertilizer. Most Westchester soils are nutrient-rich, so it’s recommended to fertilize plants once a month during the growing season.
Soil compaction is the cause of many houseplants’ misery. Repot at least every three to five years. Most commercial potting mixtures are not ideal to be used as-is in pots or beds. Make your own mixture by adding perlite or vermiculite and sand to avoid compaction and increase drainage. Check to see what percentage of each amendment is right for your plants.

Applause, please. With Judith, learning stuff out of your usual comfort zone can be fun.

(Editor’s note: Need more information? Where and how to check your plants’ needs? Many recipes are available online for making good houseplant mix beginning with bagged potting soil.

To find specific requirements for each indoor plant, reach for this classic book: “The Houseplant Expert” by Dr. D.G. Hessayon (ISBN13: 9780903505130) available at sites like Thriftbooks. It contains an extensive A-Z Houseplant Encyclopedia that lists the ideal air temperature for each type of houseplant and its light, water, and repotting needs.