This is the final article in our four-part series about indoor plant lighting. You can also read the first, second, and third articles.
You may see two other details provided in lamp specifications aside from the terms introduced in my last installment. They are not critical factors but can influence your satisfaction with how the lights look by themselves, and how plants, decorative pots, and other objects look underneath them.
The appearance of plants under the lights is not only important for aesthetics, like seeing the true colors of blooms, but also for detecting leaf discoloration, which can be a key symptom of malnutrition, light stress, or pest or disease damage.
Color Rendering Index (CRI)
While this doesn’t affect actual light intensity, it does impact our perception of how colors will look under a light and is a matter of personal preference.
On a scale of 0 to 100, the higher the CRI value a lamp has, the more accurate the colors will look compared to viewing in natural light. At the low end of the scale, colors are lackluster (desaturated) and less distinguishable from each other. Since incandescent, fluorescent, and LED lights all produce light by different means, they have different CRI ranges, though improvements in technology are closing this gap. Ideal ratings are in the 80s and above, with the 90s considered “high CRI.”
This is the second article in our four-part series about indoor plant lighting. You can also read the first, third, and fourth articles.
Typically, insufficient lighting is the limiting factor for indoor plant growth and flowering, plus the reason for spindly seedlings. Most light fixtures in our homes and offices – especially those still using incandescent bulbs or those with energy-saving bulbs that mimic incandescents – don’t give off enough energy for plants to survive or thrive on long-term. In addition, windows block a surprising amount of sunlight intensity compared with the same spot just outside the glass. Insect screening outside a window reduces intensity even more.
Artificial lighting can either supplement natural light or be the sole light source for plants. Plants tolerate levels of light outside of their preferred range, but sensitivities vary from species to species. Over time, the consequences of inappropriate light levels may impact a plant’s health and alter its appearance, even if it isn’t immediately noticeable.
The importance of light to plants
For plants, light is food. We think of fertilizer as plant “food,” but in reality, it is more akin to a multivitamin than it is a meal – it supports how they use their food (carbohydrates from photosynthesis) and helps build tissues, pigments, hormones, defensive chemicals, and so forth – but it’s not providing the calories they need to survive and grow. They certainly can “fast,” so to speak, such as spending a few days in a box in transit or remaining semi-dormant in winter, but prolonged light deprivation from insufficient lighting will have negative impacts on plant health akin to slow starvation.
Plants may lack eyes, but they can still “see” light by detecting its colors, intensity, and duration. Coupled with temperature or precipitation, it can tell them what season it is for the purposes of growth and reproduction (flowering). Weather can fluctuate from year to year, but the patterns of daylength and general light intensity remain the same and are the most reliable environmental cues for the plant.
This is the first article in a four-part series about the ins and outs of gardening under lights, both for newcomers curious about a different way to grow plants and for more experienced growers who want to build on their understanding of lighting options.Read on for the second, third, and fourth parts of the series.
Why use lights for plants?
It’s sensible to think, “why provide artificial light for indoor plants? Isn’t natural window light enough?” After all, natural light is certainly what the plants get when growing outside. If you’re fortunate and have sun-soaked windows in your home, you may have little need for artificial lighting. Anyone who has insufficient window light or who otherwise can’t utilize their windows for growing plants, though, would benefit from giving their plants brighter conditions.
We’ll address this in more detail in upcoming posts, but light levels play a significant role in keeping plants healthy, vigorous, and looking their best. Plant lights give you more control over this aspect of plant care.
Who benefits from using plant lights?
Anyone who doesn’t have ideal natural-light conditions for their plants would benefit from using plant lights (also called “grow lights”). You don’t have to be a tropical plant aficionado to make use of them, and anyone with an available power outlet can try it. Setups can be as simple or as complex as you’d like. Seed-starting enthusiasts can produce more robust seedlings, and anyone trying to overwinter a lemon tree, some herbs, an aloe, or patio tropicals could have more vigorous plants if their winter slog could be brightened with some extra light.
While it seems that everything in our world is different today than it was two months ago, one thing hasn’t changed — nature! Maryland’s stay-at-home order has given everyone the opportunity to explore their natural surroundings and given them the itch to garden to relieve tension and do something productive.
So what do University of Maryland Extension horticulturists do to stay grounded during ‘gardentine?’ Just like you, we take pictures of our flowers, gardening projects, and all things nature and send them to each other, natch!
Stephanie got us started by wishing us a happy Earth Day!
Stephanie and I went on a socially distant walk, participating in the City Nature Challenge iNaturalist project for the Baltimore area. Here are a few of the 53 species we identified for the project. Not too shabby!
Scroll over or click on the images to see the plant names.
Bloodroot with seed pod (Sanguinaria canadensis)
Dame’s rocket (Hesperis matronalis)
Blackhaw viburnum (Viburnum prunifolium)
Yellow morel (Morchella esculenta)
Sensitive fern (Onoclea sensibilis)
Sassafras in flower (Sassafras albidum)
One of my neighbors really upped the game by providing informational signs along the sidewalk for everyone’s enjoyment! Thanks, Kathy!
Virginia bluebells (Mertensia virginica)
Golden ragwort (Packera aurea)
Christa started her “Sketches from the Yard” journal on the 10th day of quarantine. She says drawing, painting, and writing about her observations around the yard and garden is a creative thing she can do at home and is something that helps her relax during these strange times.
“When I look at the details of a plant and try to document it, it gets my mind off the coronavirus news for a while and helps me focus on what is still normal and beautiful around me. I have appreciated my garden harvests of fresh greens, herbs, and even a few carrots that survived our mild winter. And the new tulips I planted last fall were delightful to see in bloom! At the end of this project, I will have a record of my garden and how meaningful it was to me as a place of serenity during this quarantine time.”
Two tulips in watercolor
Carrots in watercolor
Ranunculus in watercolor
She is quite the garden journalist! You can follow her on Instagram @mrscarignan.
Debbie is growing microgreens in a salad box on her balcony.
Miri has quite the impressive indoor garden! The ridiculous volume of houseplants keeps her sane! (Her words, not mine!) Maybe Miri will write a blog post featuring her various mini orchids and Tillandsias and include the routine she uses to keep them all so happy! (Hint hint!) She also entertains herself by secretly diagnosing plant problems on walks through the neighborhood. No photo evidence of that here!
Miri’s basement set up including a 40 year old wooden plant stand.
Tillandsia funckiana (Ya gotta love that name!)
Tillandsia ionantha ‘Druid’
Bulbophyllum pumilio, a type of orchid
Haraella odorata, an orchid with a slight citrus scent
Marian is helping her daughter plant a salad box from a distance by sharing the Home & Garden Information Center’s salad box instructions. See how you can build and plant a salad box or a salad table too!
Jon has a huge and very productive garden every year! He always gets his garlic planted in the fall.
Jon also grows his own seedlings every year and generously supplies the office with baby plants! Thanks, Jon!
Wanda enjoys tending her orchids indoors.
Wanda has lovely gardens outdoors too.
Jean has a passion for pink and her houseplants prove it!
Prayer plant (Maranta leuconeura)
‘Pink Princess’ Philodendron cutting
Hoya carnosa ‘Krimson Princess’
Chinese evergreen (Aglaonema sp.)
Ria – I sheltered in place for part of the last 6 weeks at the home where I grew up in Virginia. I went on several walks taking photos of things in bloom, but I needed to get my hands in the dirt! I had assured Jon in February that I was absolutely not going to create another garden to manage there. He had a good laugh when he saw the photos of my new garden! So much for my resolve, I needed to garden!
For the last 40 years, only daffodils and a perennial hibiscus have grown in the small triangle of space bordered by the split rail fencing, if you don’t count that sneaky Bermuda grass. If you look closely, you might be able to see the pomegranate that I got in Colonial Williamsburg about 5 years ago. It has never even bloomed, let alone produced fruit!
Please join us by taking time each day to connect in some way with nature and stay grounded during ‘gardentine’ and beyond!
By Ria Malloy, Program Coordinator, Home & Garden Information Center, University of Maryland Extension
My love affair with orchids began in college. It was the winter of 2007 while in Belize for a winter semester class “Tropical Agriculture, Conservation, and Ecosystems.” Sitting along the tranquil headwaters of the Bladen River, our guide detailed the dynamic relationship of the ecosystem that surrounded us.
In the heart of the rainforest, the delicate balance of our environment beats like a drum. As our guide described the four layers of the rainforest from the emergent layer, to the canopy layer, to the understory, and the forest floor, birds chirped and vivid blue morpho butterflies fluttered around. Our guide pointed above us to the most beautiful mesmerizing orchid I had ever seen; the black orchid.
The black orchid gently dangled off the leaning tree beside us, its greenish-yellow petals and sepals had the most beautiful purple blotches near the base. While the “lip” was shaped like the valve of a clamshell, it was deep purple to black and radiated with purple veins. I had never encountered such a fascinating flower.
After the class ended, I dove headfirst into all things orchids to absorb as much information as I could. The orchid family boasts some of the most extraordinary and diverse flowers in the plant kingdom, with around 30,000 species and 120,000 hybrids.
Generally, orchids are divided into two groups; epiphytic and terrestrial. Epiphytic orchids are usually the orchid we most frequently see (Phalaenopis and Cattleya). Epiphytic orchids use their tough roots to anchor themselves to trees. They receive nutrients from rainwater and leaf debris and they absorb moisture from the air. Terrestrial orchids grow with their roots in the ground. They are most commonly found in grasslands or boggy areas. Understanding the type of orchid you have, their growing conditions, light requirements and flowering season is integral in ensuring your success.
After much trial and error, I have learned a few things. With orchids, consistency is key. A majority of our orchids such as Phalaenopsis only bloom once a year in late winter through early spring (January to March). Getting them to rebloom is the ultimate prize as a gardener. The best way to encourage flowering is make sure that you have the proper lightening, ample water, and the right amount of food.
First, getting the light right is one of the most important factors.Phalaenopsis and Paphiopedilum like morning light from an east-facing window. This provides an orchid with a few hours of direct sunlight without hurting the plant. The sun can be very damaging to the leaves of an orchid, so the right placement is key. If you do not have an east-facing window, you can make other spots work by following these principals. North facing windows simply do not provide enough light to sustain the healthy growth of an orchid. If this is your only option, you will need a grow light to give your orchid the boost of light it needs. If your orchid is in a west-facing window put up a sheer curtain to protect it from the heat of the summer sun. Furthermore, if using a south facing window a sheer curtain is advisable year round. Unlike Phalaenopsis and Paphiopedilum, Cattleya like bright light from a south or west facing window.
Just as getting the right lighting is crucial so is watering. When watering your orchids, always water in the morning. This guarantees that the moisture has time to evaporate. If you water at night, it allows water to settle in the nooks of the bark, which promotes fungal growth. Avoid watering or misting the leaves. Misting tricks the guard cells on the leaves to think that the humidity is higher than it actually is. This can cause your orchid to dry out faster. Additionally it can lead to crown rot if water settles in the nooks of the leaves. Orchids love humidity. To increase humidity you can use a humidifier set at 40-50% or use a humidity tray.
All plants require nutrients to grow and thrive. Epiphytic orchids like Phalaenopsis live in trees where they receive nutrients from rainwater and leaf debris. Pot-grown orchids depend on feedings to produce healthy leaves and beautiful blooms. With proper feedings, a well-fertilized orchid will keep their leaves longer and will produce more flowers. When feeding, it’s best to use orchid-specific fertilizers. Orchids also thrive from “weakly weekly” feedings when blooming by diluting fertilizer to ¼ strength rather than a full dose once a month.
There seem to be new lighting choices for indoor plant growing every year. If you’ve been starting annual flower and vegetable plants indoors you probably learned early on that natural light entering through windows is hardly ever adequate. Some type of supplemental light is essential to produce healthy transplants. But what types of bulbs and fixtures work best? And how much money do I really want to spend on something I’ll use for 8-12 weeks each year?
Many gardeners use 2 ft. or 4 ft. long fluorescent tubes in a fixture (a.k.a “shop light”). The T number is the tube diameter in 1/8 inch units. The traditional T12 tube (1 ½ in. dia.) has been largely replaced by slimmer T8 (1-inch dia.) and T5 tubes (5/8 inch dia.). All fluorescent tubes give off a small amount of heat– rarely a problem, even when foliage grows into them. Heat from the ballast in the fixture can help hasten germination and plant growth, especially when your set-up is covered with plastic.
LED grow lights
Light-emitting diodes (LEDs) give off very little heat, use less energy than fluorescent tubes, and last about twice as long. They are also mercury-free and made from plastic so won’t shatter like glass. LEDs appear to be the wave of the future for indoor lighting. Horticulturists and lighting engineers are working worldwide to customize wavelength combinations for specific plant production goals in commercial greenhouses and indoor vertical farms. Continue reading →
Both my sons enjoy growing plants inside their apartments – all that botanical indoctrination paid off! My younger son, Patrick, has now managed to grow food in his sunny 21st-floor Chicago flat: a nice little harvest of cucumbers.