By Benny Pino
This article originally appeared in the April 2019 issue of Groiwng for Market Magazine
Have you ever lost precious seedlings in your greenhouse to frost? How about tossing a flat or two out due to heat stress or a missed watering? Or better still, stared at a tray of seeds that won’t germinate, with smoke coming out of your ears, because you’re sure someone (not you!) mis-watered them at a critical moment? Have you ever shrugged to yourself reading the growing instructions on a seed packet that says “Germinates best at 70 Fahrenheit” while standing in your 85-90 degree greenhouse? You’ve started to look into a germination chamber to solve some of these issues, but they look pricey and have limitations like not being able to handle as many flats as you’d like to start at once.
This is starting to sound like an infomercial, isn’t it? Don’t worry, we’re not going there! But we are going to talk about how we used grow lights to solve these issues that we faced time and time again, season in and season out, here at Loblolly Farm. After years of using grow lights we can confidently say we’ve not only worked through these challenges, but honed a system that produces strong starts reliably and affordably.
Grow lights for spring starts
Grow lights can be the solution to challenges managing starts during frosty springs. If you have the space in your house, especially in the basement, it is hard to understate the convenience of having your spring starts indoors. Consider not having to change into several layers of winter gear to get out to the greenhouse. How much more often would you look in on your starts if they were a warm 50 feet away from your couch?
Also consider the plants. How warm do you keep your greenhouse in spring and how much does it cost in propane every year? What if you could save those fuel costs and manage the growing environment of the seedlings at between 60-70°F? Even if your basement were 40-50°F the lights would suffice in heating your transplants to optimal temps.
You can also raise and lower the lights with a simple pully system and control the temperature of the seedlings. We have used these fine-tuned environmental controls to great advantage in ensuring strong germination and optimizing growth rates. Also, heating mats become a thing of the past. No need for a germination chamber. No raising and lowering the sides of a greenhouse.
Grow lights for summertime
Another major advantage we’ve discovered, almost entirely by accident, is bottom watering. We came to bottom watering by necessity - it becomes obvious when working with lights that you need to put trays into holeless flats and water from below because electricity and water don’t mix. We’ve seen people get shocked when getting careless with watering around grow lights, so we strictly bottom water.
What we didn’t realize is that it would drastically reduce our watering chores, especially on sunny summer days. We went from needing to water as many as three times a day overhead to bottom watering every other day. While there is some technique involved, we can say from years of doing both that bottom watering correctly is not only simpler, it also delivers an even application of water every time. You will also see far less overall seedling heat stress throughout the season, and you can schedule watering just once a day, instead of having to keep an eye on the weather to determine how much to worry about the greenhouse.
We also grow a great deal of hardy annual flowers. These are cool season transplants that are put into the ground in late fall to overwinter and flower first thing in the spring. See a problem here? If you do you spotted it faster than us. How well do cool weather plants do germinating and growing in a summertime greenhouse? Not so hot, let’s put it that way. We’ll bet you’ve also already guessed the solution. Even if you don’t grow flowers, we know it’s the same with any cold hardy transplant - wouldn’t it be nice to start them whenever you think it’s best and not have to worry about them getting cooked?
Grow light basics
The first question to ask when considering grow lights is; what do you want to grow? In this article we are only addressing growing plugs up to 8”, or two-to-three true leaf pairs, or transplants no larger than 72 cell plug trays. We do not have much experience in growing transplants any larger than this with T5 Fluorescents.
When looking into grow lights you are going to come across horticulture lighting metrics. Just do a search online for grow lights and you’ll see every listing has a paragraph of jargon in the listing title alone. DLI, PPFD, watts, lumens, kelvin, kWh – just to name a few.
Taking the time to familiarize yourself with these terms would give you more ability to make informed decisions with your lights, but it can be confusing, time consuming, and there is a lot of misinformation out there. We’ve seen multiple warnings now from review sites; there are many snake oil salesmen who often misuse the scientific terminology and will outright lie about the output of their lights. Please take heed, if it sounds too good to be true it likely is.
Not to worry though! You don’t need to learn the jargon, nor do you need to sift through heaps of lousy lights. Ultimately, you just need to go purchase from reputable companies. We purchase from Hydrofarm for T5s, and Thrive Agritech for LEDs. We’ll cover the difference between these two options. We will not cover T8s or T12s as their light output is ultimately deficient, nor HID lights like metal halide and high-pressure sodium lights since they are more powerful than needed for starts, are expensive, and consume electricity inefficiently.
T5 fluorescents vs. LEDs
Our grow light set up here at Loblolly consists of four shelving units with four shelves apiece. Each shelf has a 2’x4’, eight bulb, T5 Hydrofarm fixture. The fixture fits over the shelf snugly and each shelf can fit 4 standard size flats (such as 10x20 128s) with bottom water trays. As of this writing these eight bulb fixtures retail for about $150. So, the total price of our 16-light setup, with hardware and shelves, cost roughly $3,000. In Maryland the cost of a kilowatt hour is roughly 13 cents. Each unit requires 432W per hour to run so it costs roughly $1/unit/day.
54W x 8 bulb : 432W x 16h : 6,912W / 1000 x $0.1392/kWh = $0.96 per shelf per day
You might suppose then $0.96 x 16 = $15.36 for 16 units per day, but the reality is we often have only half to 2/3 on at any given time as they don’t need to be on for most germination, and for the first 1-2 weeks only 4/8 of the lights on a unit need to be on. So it works out to roughly $10/day, hence $10 x 30 = $300 per month.
LED lights are several orders of magnitude more efficient than this but require more up front in investment costs. Each Infinity 2.0 unit, which is 4’ long, costs about $200, and you need 2 per shelf to have enough light to grow starts. So startup investment for the same 16 shelves would be about $6400. But to run each light only requires 65W for a total of 130W/shelf vs. the 432W of the fluorescents. That’s 3.3 times more efficient.
65W x 2 bulb : 130W x 16h : 6,912 x / 1000 x $0.1392 = $0.29 per shelf per day
$0.29 x 16 shelves : $4.64/day rounded to $3/day due to units being off intermittently, giving you $3 x 30 = $90.00 per month.
This means you save $200/month in energy costs. We run our lights half the year so 6 x $200 is a savings of $1200/year. Divide $1,200 into the price difference of $3,400 between the lights and in only three years you will break even. For every year after that you will save $1200.
In addition, Thrive Agritech LED lights are waterproof, last for 2-3x longer (65k hours), and most importantly - run considerably cooler. As in 20°F cooler! While we have managed to work around the heat of the T5 bulbs you should be warned, they can make the ambient air 90+ degrees F and need to be raised at least 9” to 1.5’ above your plants. Fans placed near the shelves help, and keeping them in a basement or air conditioned space can help negate this heat.
Setting up grow lights
We do not feel it’s necessary to purchase expensive hardware for hanging your lights. We have purchased $75 72’H x 48’ W x 24’ D heavy duty garage shelves that are adjustable. They come with particle board shelves which should be replaced with plywood for durability. We then use two #8 screw hooks and insert them into the underside of the shelf we are going to hang the fixture from.
One power strip can be used to connect every two shelves to an outlet. Be sure not to overload a standard 110v outlet with more than six T5 fixtures or they will turn off or trip the breaker. Depending on the amperage of the circuit you might have to do a bit of plug and play to see where you have enough power to run your setup. If you are looking to run a lot of lights (20+) it would be advisable to invest in LEDs as their energy requirements will be easier to meet. While we have not faced any challenges with our 16 T5 lights, consult with an electrician for larger setups.
Installing a simple light timer is critical. Most research we’ve found suggests running your lights for 16 hours a day. Dimmers can be installed with the Infinity 2.0 LEDs, and they seem a smart way to go if you’re confident you’ll remember to adjust them as your plants grow. Another option is buying adjustable grow light hangers which use a simple pully system to change the height of the lights. We use them for some lights to get them closer to trays.
Lastly, we advise you focus on growing small starts, no larger than those produced from a 128 tray. What we prefer are paperpot trays, since they have 264 cells apiece and use the full real estate of the shelf, whereas most nursery trays come up shy. With this technique we have over 4,000 transplants on one shelf/8 ft2 of floor space. If we were running flat out we could fit 16,000 plants on our four shelves/32 ft2 floor space.
Can a grow room replace a greenhouse?
This question should be considered carefully on a case by case basis. On most farms, greenhouses are one of the most expensive infrastructure investments. We were looking into several greenhouses and found an 18’x48’ ranged from $4-8k, and getting a 100 gallon propane tank installed was going to cost $500-1,000 and that’s not including fuel. That’s about 3x the price of starting with our example of 16 T5 shelves, or 50-100% more than using LEDs.
A 18‘x48’ greenhouse has 864 ft2 inside (~600ft2 after paths) vs. 128 ft2 of shelf space. Per ft2 the greenhouse (assuming $6k total and 600ft2) is $10/ft2 and the shelves $23.50/ft2 (for T5s, or $46/ft2 for LEDs). For simplicity’s sake let’s say our $600/year in utility costs for the lights vs. propane for the greenhouse is a wash.
Even after accounting for the cost of tables, a greenhouse would cost half to a quarter as much per square foot but require 50-100% more upfront capital. It would also give you 500ft2 more to work with. Lastly, of course, you need a room to put the shelves in. If you were to build an insulated shed with power it would cost $1-2k for a 10’x10’.
This should make clear why we suggested small starts earlier. Grow lights are not a great system for growing large plants like tomatoes or cucurbits past a few weeks. A hybridized system where a greenhouse is used for larger starts and the rest of your transplants are grown under lights could be a nice fit.
In this case you could instead source a small greenhouse for $2-3k. You can also experiment with growing starts in smaller cells than you thought previously possible, we’ve done just that and found it to be worth it. No potting up, less pricey potting soil, and as long as you water them well, they’re just as resilient and roughly the same days to maturity.
We grow all of our flowers under lights and don’t miss a greenhouse one bit, but we’ll see what the future will hold. If you have questions please don’t hesitate to reach out, we’ve had to do hours and hours of reading and make all sorts of mistakes just to come this far. There’s much yet to learn in this space and we look forward to this technology continuing to improve. Here’s to healthy starts and a prosperous 2019!
A brief history
Our experience with grow lights started over six years ago, and began where many do, with a rudimentary daisy chain of fluorescent T8 or T12 shop lights. At that time we relied on Nancy Bubel’s 1988 publication, The New Seed Starters Handbook, and just as she described in her book, we were hooked as soon as we started. We were now able to start seeds 6-8 weeks before the growing season without having to use a heated greenhouse. Not only was indoor growing of starts less expensive than propane, we now could be sure we wouldn’t lose seedlings to a late frost from mismanaging greenhouse heating.
While Nancy’s book shed light on some important aspects of using grow lights at the time, her information and hence our results were limited by 1980s technology. We dealt with considerable issues like leggy seedlings when there wasn’t quite enough light to cover every aspect of the trays. And then if we timed our starts too early or the ground took too long to thaw the seedlings would eventually outpace the amount of light the fluorescents could produce.
Worse still, we needed to constantly adjust the lights to be practically touching the plants or they again wouldn’t get enough light. It was worth it to save the money and stress of greenhouse growing, but by no means an ideal circumstance. We have met many growers who still use this system as they are invested in it, and information on grow lights for agriculture is often not as readily available as other cultural practices.
There came a point two years ago when we were about to throw in the towel entirely and give up on the lights since it seemed like all of our peers were managing with greenhouses. But then we stumbled upon an article in on a review site called Wirecutter by Meg Muckenhoupt titled “The Grow Lights We Like.” The article gave timely information and stated, “After more than 50 hours of research and interviews with five experts - including one who designed plant lighting for Antartica and the moon- I can say the Hydrofarm Commercial T5 fixture…is the one we would buy if we were starting seeds indoors.”
It is the light we still use today and although we will eventually switch over to LEDs since they are the most effective lighting source being developed, we are happy with our decision to use Hydrofarm’s T5 lights, and feel like within many small scale commercial farms they can fill an important production niche. We now use our grow lights to produce all of our farm’s starts and don’t even own a greenhouse. When we scale up production to larger than an acre, we will invest in a greenhouse so we can move 2+ week old seedlings from under the lights, so we don’t have to pay the energy costs for larger seedlings.
Benny and Courtney Pino run Loblolly Farm in Maryland, growing cut flowers and designing weddings. Visit them on the web at www.Loblolly.Farm or on social media @LoblollyFarm.