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 third in our four-part series of articles about indoor lighting for plants. You can also read the first, second, and fourth articles.
Artificial light sources come in several forms, all relatively easy to acquire. Costs can vary wildly, and some are more electrically efficient than others. The variety of available options allows you to customize setups to your needs and the preferences of your plants. Before you dive into an overwhelming list of web search results, here are traits of the basic categories:
Light-Emitting Diode (LED)
best energy-efficiency in terms of light produced per watt consumed (especially if the light has the ideal spectrum)
coolest to the touch except for high-powered units, which usually have small built-in cooling fans
can be expensive for high-quality fixtures, though costs are decreasing
light output does not dim significantly over time, though diodes do have a finite lifespan
reach full brightness immediately or very quickly when turned on
diodes can either be exposed or under a frosted or textured cover to help diffuse the light
diodes are directional, meaning they don’t emit light in every direction the way a fluorescent tube does, so reflectors aren’t usually needed
more even light output from one edge of the fixture to the other
can be round like a spotlight (with a cluster of diodes) or straight strips (or strips inside a tube) with one or more rows of diodes
some replacement “tubes” can be used in place of fluorescent tubes in a fluorescent fixture, but you must check with the fixture’s manufacturer for compatibility as mixing components is a matter of electrical safety
Happy New Year! It is hard to believe that we are already in a new year. We are kicking off our third season by sitting down with Extension Educator Ginny Rosenkranz. Like many of you, during the pandemic our acquisition of houseplants increased exponentially. Ginny guides us on caring for all of our botanical beauties.
We also have our:
Native Plant of the Month, Musclewood, Ironwood (Carpinus caroliniana) at ~24:55
Bug of the Month, Ice crawlers or ice bug family Grylloblattidea at ~29:05
For more information about University of Maryland Extension and these topics, please check out the UME Home and Garden Information Center website at https://extension.umd.edu/hgic.
The Garden Thyme Podcast is a monthly podcast brought to you by the University of Maryland Extension. Hosts are Mikaela Boley- Senior Agent Associate (Talbot County) for Horticulture, Rachel Rhodes- Agent Associate for Horticulture (Queen Anne’s County), and Emily Zobel- Senior Agent Associate for Agriculture (Dorchester County). Theme Song: By Jason Inc.
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.
Uh oh. You need a last-minute gift or a tiny tree to brighten a corner of your holiday home. Here comes a Norfolk pine to the rescue. Whew. That was close.
Looking like miniature Christmas trees, Norfolk pines pop up at garden centers and other stores over the holidays. Bedecked with bows and balls, they’re festive and cute as can be.
With a graceful, pyramidal shape and tiers of gently arched branches, they are loaded with appeal. They look delicate but are actually tough, long-lasting little trees.
Technically a Norfolk Island pine, this pint-sized evergreen is native to – you guessed it – a place called Norfolk Island, just east of Australia. Captain James Cook discovered this tree on his second expedition to the South Pacific in 1774.
Norfolk pines are subtropical, hardy in zones 9 to 11. So they can’t handle our winters but are happy to summer outside and hang out with us indoors when the mercury drops.
They are fairly carefree houseplants. Put them in a bright spot with some direct light. Water them when the top inch of soil feels dry.
Norfolk pines love humidity, so mist them or group them with other plants. Fertilize them every week to two from spring to fall.
Transition them to outdoor living in the summer by putting them in the shade for a few days, then introducing them to bright light. Just remember to keep them watered and bring them in before the first frost hits.
Norfolk pines’ roots resent disturbance, so repot them only every few years. Once they get three feet tall, replace only the top few inches of soil instead of repotting the whole plant.
They are slow growers. Norfolk pines generally top out at three to six feet indoors, but they take their sweet time getting there. In their native climes, they can top out at 200 feet.
Oh, and did I mention that a Norfolk pine is not a true pine? Technically Araucaria heterophylla, is part of a genus of 19 species of pine-like conifers.
But let’s not split botanical hairs.
The Norfolk pine is an appealing tree. For those with small spaces, it’s an ideal Christmas tree. For the rest of us, it is just a tiny charmer, a sweet little elf of a tree.
Big or small, I hope your holiday tree is the center of a warm and blessed holiday season spent with family and friends.
By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.
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.
A variety of plants growing under an LED light indoors. Photo: Miri Talabac
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.
Christmas cactus are popping up everywhere. They’re lovely living gifts that enliven holiday décor and add beauty year-round. If you like floral irony, this is your plant. Even though they are fleshy succulents, they originated not in arid regions but in the rainforests of Brazil where they drape themselves over tree branches as epiphytes.
Arching stems give Christmas cactus – and this Thanksgiving cactus – handsome structure when not in bloom. Photo credit: Washington County Master Gardener Lauri Ricker
As with many tropical plants, Christmas cactus delivers a double dose of drama. The first is the strong architectural form of arching stems made up of a series of scalloped pads. But it’s their cascading flowers in pink, salmon, red, or white that are the real showstoppers. Stacked layers of swept-back petals with prominent stamens, they are very oh-la-la. They also have a long bloom time, flowering from two weeks to two months.
Heavy blooms are a hallmark of Christmas cactus and its cousin, this Thanksgiving cactus. Photo credit: Washington County Master Gardener Wilma Holdway.
Also long is their lifespan. They can live for decades, often becoming family heirlooms. I once received cuttings from a plant started by a – ahem – mature friends’ grandfather. This caused a commotion at airport security. What IS that thing on the x-ray? And yes, the kindly man let me keep my cuttings once I showed them to him and shared their story.
Christmas cactus has beautiful cascading blooms. Photo credit: Washington County Master Gardener Leora Smith
Care is fairly basic. They like bright indirect light, not full sun. Keep the soil slightly moist. Mist regularly or put the pot on a dish of moist gravel to boost humidity.
Christmas cacti need cooler temps and less water to nudge them to bloom again. They need a chill to give you a thrill.
Master Gardener friends report that the natural drop in temperature and day length in fall is enough to encourage buds indoors. Others let their cactus summer outside in light shade, keeping them out until fall temperatures drop to 50 to 55 degrees. Regardless of how you stimulate flowering, resume regular care when buds form. After your cactus finishes blooming, give it a cooler rest period and less water for two months.
And yes, Christmas cactus has many cousins including Thanksgiving cactus and Easter cactus, all named for the times they bloom. Mine never consulted calendars and bloomed as they liked.
How can you tell which cactus you have? Easter and Thanksgiving cactus have pointed edges on their leaves while Christmas cactus leaves have more rounded scalloped edges.
Thankfully, Christmas cacti are a snap to propagate, so they are easy to share. Just break off a stem at a joint, slip into well-drained soil and keep the soil moist. It will root in a few weeks.
I love a good story, and these plants have several. My favorite is a Brazilian legend that tells of a poor boy in the jungle who prays repeatedly for a sign of Christmas. One day he awakes surrounded by colorful flowers on the tips of cactus. And so the cactus became a symbol of answered prayers.
So Christmas cacti are a symbol of hope. With their long lives, colorful blooms, ease of care, and sharing, they make wonderful gifts for friends, family, and your very own green thumb.
Annette Cormany, horticulture educator, University of Maryland Extension – Washington County
