About Correct Lighting your Herb Garden
Growing Herbs for Beginners – Part 3
Providing sufficient quality lighting is one of the most critical aspects of growing herbs indoors. Yet, the importance of providing the correct amount of light to herbs indoors is often overlooked especially by beginning indoor herb gardeners.
Growing herbs indoors present for obvious reasons (lack of sunlight) specific light challenges, much more so than outdoor herb gardens. When starting out, you may have as many questions as I did: what do I need? What should I consider? What is a good light really? …
Some basic knowledge about light makes things a lot easier.
In this post I will share the basic lighting knowledge that I have learned and that I use to successfully grow herbs every day:
- about the importance of sufficient quality lighting
- about good solutions to make herbs thrive indoors.
When it comes to explaining light requirements, herbs and plants are basically the same. So in this post I may mingle the use of the words herbs and plants.
How important is good light to make herbs thrive?
The energy of light (sunlight or artificial light) directly influences plant growth by inducing the natural chemical process of photosynthesis. This process converts water and carbon dioxide into organic compounds (glucose plants use as food) and releases oxygen into the atmosphere.
Without light, natural or artificial, there is no photosynthesis possible. Plants wouldn’t be able to grow and produce oxygen.
Thus, plants are pretty dependent on light to grow and survive.
Light levels will vary depending on the time of the year and the location where the light level is measured. It can vary from very strong, like on a sunny summer day outside, to very low, like on a cloudy winter day indoors away from a window.
That is why it is important, for all beginning indoor herb gardeners as for every plant lover, to have a good understanding of the light requirements of herbs:
- what is good light quality: the correct light type for indoor herbs
- what is correct light exposure: the right amount of light required for indoor herbs
- what are the consequences of under or overexposure
- how to solve incorrect light levels indoors.
I absolutely don’t want to attempt to create a long scientific article here, but rather a resume of all the necessary basics that will allow you to make the correct choices for your indoor herb garden:
- a good location
- if necessary, choosing correct lights
This knowledge could mean the difference between herbs that thrive and produce a beautiful, healthy harvest and herbs that shrivel up and die.
What kind of lights do herbs (plants) need?
You will probably remember the physics class we all had when I tell you that not all light is exactly the same. You can see this when looking at the light spectrum picture below.
Both the visible and the invisible light (measured in nanometers, corresponding to wavelength) falls somewhere on this spectrum.
Let’s explain what sort of light herbs actually need.
We as plant growers are interested in light that plants can actually use for the so important photosynthesis. This light ranges from 400 to 700 nanometer, and is also known as the Photosynthetically Active Radiation, or PAR.
- The blue light (400-490 nm) is used by plants primarily during the grow phase (development of leaves)
- The orange, red light (580-700 nm) is used by plants during the flowering and fruiting phase
You notice that the green light (in the gap between 490nm and 580nm) isn’t used by plants. This is caused by the chloroplasts in their cells, these cells absorb blue and red light, but reflect green light. This is actually the reason why most plants are green.
Sunlight gives off all wavelengths of visible light and is thus an ideal source of natural light for plants, promoting good plant growth.
Man-made lights emit light with specific wavelengths depending on the manufacturers design of the light. Some of these artificial lights will be more suited for plant growth than others. The best lights are probably the ones that most accurately replicate natural sunlight.
But as mentioned above, the growth of plants is mainly affected by light that falls into the “blue” spectrum of the light scale. Daylight, fluorescent light and grow lights all have some “blue” tones in them and will help provide the light your plant needs. Incandescent and halogen lights on the other hand are more “red” and will not help your plant grow.
So let us remember that the color of the light does affect plant growth. And that purple and blue light stimulates the vegetative (leaves) growth phase while the yellow-orange-red light stimulates flowering and fruiting.
How much light do herbs need?
The quantity of light a plant needs depends of course on the individual plant. In general, flowering plants typically require more light – red light especially – than foliage plants.
The growth of plants, stimulated by light of the correct wavelength (blue and red) depends also on the duration and the intensity of the light. And both parameters are actually connected: you will realise that in certain circumstances “high intensity x short duration” equals “low intensity x long duration”.
Duration
The duration refers to how long the plant is affected by the light source.
Intensity
Intensity refers to how strong the light is. The intensity can vary on the type of light and the position of the light.
In a lot of plant books, plants are classified in terms of light requirements based upon the need of sunlight during a day: full sun, partial sun, partial shade, or full shade. Although these classifications are made for outdoor plants we can also use it as an indication for indoor light requirement.
According to garden books, full sun plants require a spot receiving six or more hours of direct sunlight each day.
Many herbs are classified as full sun: Rosemary, Lemongrass, Sage, Marjoram, Oregano
This means that, when put indoors, these herbs prefer a south window spot.
Partial sun and partial shade plants require a spot that receives between four and six hours of direct sun over the course of the day.
Translated to our indoor herbs, the following herbs are classified as partial sun partial shade: Catnip, Chamomile, Dille, Fennel
This means that, when put indoors, these herbs prefer an east or west-facing window.
And finally, full shade plants want less than four hours of direct sunlight a day. North facing windows are appropriate locations for the following plants preferring full shade: mint, parsley, cilantro, thyme, chives, and lemon balm.
Using a grow light
When we use grow lights, the distance of the light will determine how much surface area is covered. It depends at what distance you place your grow light from your plants.
The distance will also influence the intensity. The closer the more intense.
Getting the position of your grow lights correct comes with experience, because it requires some balancing between the heat output, intensity, and overall footprint of the light.
In nature, the seasons will change the period that photosynthesis occurs. With grow light we determine how much light we are giving our herbs in a 24-hour period.
Changes this period are a trigger for some plants, for example signaling to the plant that it’s time to start fruiting or flowering.
What are the consequences of under or overexposure
Consequences of too little light
Sometimes a plant will not get enough light and will have problems with too little light. Plants affected by light shortages or too little blue light will have the following signs:
- Stems will be leggy or stretched out
- Leaves turn yellow
- Leaves are too small and spindly
- Brown edges or tips on leaves
- Lower leaves dry up
Plants that are denied sufficient light will eventually lose their color and die. Plants deprived of light will grow upward, stretching their stems more rapidly than usual, searching for light.
Consequences of too much light
While plants need light in order to survive, it is possible for plants to be exposed to too much sunlight and be sunburned.
The foliage of the plant will begin to fade, bronze, or crisp.
Grow lights
Sunlight is undoubtedly the cheapest source of light for growing plants but it is not always available in our homes.
With a good indoor grow light, it is possible to grow herbs effectively all year round!
In this part I will not go over all types of lightbulbs and growlights exist on the market but I will try to answer two questions, that I received frequently, as simply as possible: “Do I need grow lights?” and “What grow lights should I buy?”
Do my herbs need grow lights indoors (maybe during the winter)?
The short answer is, not necessarily – but it can be a good idea. If you have a window that gets bright light all day your herbs will grow just fine even in winter. However, the days do get shorter so they won’t get as much light as they did in the summer.
If herbs don’t get enough light they start to stretch out and they will finally stop growing.
A grow light can be a great way to keep your herbs growing.
I wanted to continue growing herbs indoors also during the darker winter days so I decided to invest in some grow lights.
What grow light did I buy?
There is a lot of information out there on the internet about what type of grow lights to use, how much light you need, what color the light should be, how far away should the light be, and so on.
It took a while figuring out what exactly is needed. Based on some helpful articles I have tried two types of grow lights up till now, with changing results.
The first one was based on my research and rather focused to be an inexpensive but not so efficient solution. And one of the lights stopped functioning relatively quick…
The second solution was a gift from my wife, and is more a design solution, to cope with the lack of light during winter. This light is quite ok for already developed herbs but I felt it wasn’t ideal for seed starting. The light was often too far from the seedlings resulting in leggy sprouts.
So I got the idea to build my own DIY grow light system also ideal for seed starting. You can read all about this setup in my extensive article about my seed starting & grow light system.
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Conclusion
In conclusion, it is my experience now that grow lights are a great way to supplement the natural light your herb plants are already getting, especially in the winter. I wouldn’t be able to experiment with growing herbs during winter, and wait for spring and summertime.
I hope that with this basic knowledge I have shed some light on the importance of quality light for growing healthy herbs outdoors but especially in your indoor herb garden.
What is next?
This ends part 3 of 3 of the Free Online Course “Herb Garden for Beginners”. This last part was mainly focused on basic knowledge about correct light for your herb garden.
Thank you again for being part of the course. We are on this journey together with all like-minded people so let’s help and assist each other.
That is why I have one request for you to improve this 3-part course and even better serve other beginning herb gardeners: let me know in the comments below what can I help you learn about next (topics, struggles,…)?