The Coastal Gardener: Shedding light on growing plants

Working at a nursery, a common question is “can I grow this indoors?” Usually the plant in the customer’s hands is something like a florists’ hydrangea, miniature rose or chrysanthemum. Sometimes it’s even a dwarf lemon; often it’s a potted succulent.

Almost universally, my answer is “no, not for long, it needs to be outdoors in the sunlight and fresh air.”

Customers often either don’t like that answer or don’t believe. Often the ensuing conversation continues with “why?”

I usually say something like, “There are a lot of differences between indoors and outdoors. First, there isn’t enough light indoors, but there’s also a lack of air circulation and adequate humidity inside a home.”

Customers, God bless them, usually pick up on the first comment about a lack of light and respond with something like, “Oh, I have a really bright room and it has lots of windows and light; I’m sure it will get enough light.”

Truth is, a plant growing indoors is in dramatically lower light than the same plant growing outdoors. Even if the plant is at a window, unless you don’t have a roof on your house, it’s only receiving at a minimum a half day of direct light, usually much, much less.

Is there anything you can do about the lack of light available to a plant grown indoors?

Plant lights, or “grow lights”, are artificial light sources that replace the sun’s natural light. They are designed for growing plants indoors. Artificial lighting may be a necessity if you want to grow traditional outdoor plants in indoor environments. Plant lights are also helpful if you want to produce healthy seedlings or transplants indoors, especially during the short, often cloudy days, of late fall, winter and early spring.

Plant lights use special bulbs, usually fluorescent, halide, high-pressure sodium, or LED, which are quite different from incandescent or compact fluorescent bulbs. Plant lights emit either cool or warm light. Cool light, which is primarily in the blue spectrum, is good for promoting leafy growth; while warm light, primarily in the red and orange spectrum, is important for developing flowers and fruit. Plants do not actually use the full spectrum of the sun’s light, only the red/orange and blue ranges.

Standard fluorescent lights, even those right off the store shelf, are good for seedlings and low light foliage plants. Nonetheless, fluorescent lights generally can’t deliver the strong light needed to grow plants much taller than 6 or 8 inches. Fluorescent lights are popular because they are inexpensive a do not heat up, allowing the light to be extremely close to the plant without damaging it. The closer the light, the more benefit to your plant. Fluorescent grow lights are some of the most commonly used lights for indoor gardening. If you are growing vegetable or flower seedlings under a standard two-bulb fluorescent fixture, you can usually achieve a good color balance by combining one cool white and one warm white bulb.

Metal halide and high pressure sodium plant lights are the most efficient and productive lighting system available to take plants from seedling all the way to maturity. Metal halide lamps emit cool blue/green/violet light, simulating daylight. High pressure sodium lights supplement halide lights with red/orange light. Experts use metal halide lights for a plants growing cycle, then switch to high pressure sodium lights during the blooming and fruiting phase. Used in street lighting and industrial use, these bulbs provide a huge amount of light.

While fluorescent bulbs can be within a couple of inches of a plant, metal halide lights must be 12 to 18 inches away or they may burn. Metal halide supports nice, healthy plant growth up to two feet or so, and plants will reach this height more quickly than with fluorescents.

LED grow lights deliver only the colors of light (wavelengths) plants use most efficiently for healthy growth. This grow light uses very little energy, and still provides all the light your plants need for vigorous growth indoors. LED grow lights are a good choice if you are interested in growing indoors without a lot of hassle. Traditional grow lights generate a lot of heat and use large amounts of electricity, but LED lights run cool and use little energy. LED bulbs last up to 50,000 hours and are recyclable after they finally fade out.

If you love to grow your own plants, indoors and out, consider setting up some indoor plant lights. You can put up a tiny little system on your kitchen counter to grow salad greens and herbs. You can use another system to start the seeds of your rare French Haricots Verts beans, your pricey Italian tomatoes and your rare delphinium seeds from England. You can even convert an entire room to grow those lemon trees and specimen-sized succulents.

RON VANDERHOFF is the nursery manager at Roger’s Gardens, Corona del Mar.

Ask Ron

Question: When is the best planting season for hollyhocks?

Trixi, Newport Beach

Answer: The good news is that you can plant hollyhocks just about any time of the year. Most commonly, hollyhock seeds are planted in spring; transplants planted in either fall or spring. The bad news is that hollyhocks are biennial plants. In other words, they are two year plants. The first year they just grow leaves, the second year they flower, then set seed and start over. So to save a little time you might look for transplants. If you get them in the ground in the next couple of months, they will almost certainly bloom late next spring or summer. Give them a sunny location with excellent air circulation. If you can avoid overhead watering you’ll have a bit less trouble with a common leaf disease called rust.

ASK RON your toughest gardening questions, and the expert nursery staff at Roger’s Gardens will come up with an answer. Please include your name, phone number and city, and limit queries to 30 words or fewer. E-mail stumpthegardener@rogersgardens.com, or write to Plant Talk at Roger’s Gardens, 2301 San Joaquin Hills Road, Corona del Mar, CA 92625.