I have, on occasion, been asked how I can manage to fit so many houseplants into my living space. It's a fair question. The answer hasn't always been clear to me, either. I've been thinking about it again lately because a reader asked (by e-mail) a couple weeks ago, and it occurred to me that this is something I hadn't addressed yet on the blog, exactly how I manage to stack plant upon plant in a way that enabled me to get 550 or so in a two-bedroom apartment.
There are three key components of my set-up. The first is simple and obvious: small plants take up less room than large ones. If you just want to impress people with how many plants you have, get a bunch of 3- and 4-inch ones and call it a day. This isn't quite how I do it -- I think just by the amount of space they take up, my 6-inch plants are probably the bulk of the collection -- but there are quite a few 3s and 4s, especially among the succulents.
The second part is: four-foot shop lights. They're easy to find, and can be had for about $10 if you shop around a little. Four-foot fluorescent bulbs are not cheap, but they also last for a long time,1 and fluorescent light is perfectly adequate for a lot of different plants as long as it's not too far away from them, so they're cost-effective in the long run.
(I am not, by the way, a fan of the special "plant lights," formulated specially to produce extra-large amounts of the red and blue wavelengths plants need. They're outrageously expensive, for one thing, and I also don't like the unnatural purple color. Regular cool white and warm white bulbs2 do just fine.)
The third part, and arguably the most important from a plant-density angle, is: shelving.
I use wire shelves. I don't really have a good name for the particular product (The last boxes I bought said they contained "black wire storage," which amused me: finally! A place to stick all those annoying black wires!), but they're sold in a lot of different places: I've seen them at Lowe's, Menards, Target, etc. There are often a range of different sizes: usually a given company's shelves will fit together regardless of whether you have them all the same size or not, but it's worth paying attention to. (You should definitely try to make sure you're getting all the same color, and from the same manufacturer: this will save you trouble later. I've seen them in black, chrome, and white.) I recommend six-foot tall (72"), for the simple reason that six-foot is usually as tall as they get, and if maximum plant density is a goal, more height is better than less height. The widths vary, though they're usually three-foot (36") or four-foot (48") wide. Four foot is better if you're going with the standard four-foot shop lights. Three-foot may be more suitable for a window, if you're relying on natural light and don't have to worry about fitting shop lights on there.
As packaged and displayed, these shelving units are usually just four poles and four or five shelves, which can be placed more or less anywhere on the poles, so you can adjust the heights of the shelves to your individual needs. I've found that sometimes I don't want to use all the shelves they include: five shelves over a span of six feet means that the average distance between shelves is only 5/6 foot, or ten inches. You might be surprised at how few of your houseplants are under ten inches tall. However, if you buy two sets at once, there's a trick you can use to get much more usable space, which is that you can connect the two sets of shelves with a third set in between:
This way, instead of having ten shelves that are all only 10 inches apart on average, you have ten shelves that are all 21.6 inches apart (72*3/10) on average, which is much more useful spacing for your average houseplant. You can continue this if you want to, and buy a third set of shelves, and connect them twice across the gaps, which puts your spacing at 24 inches apart (72*5/15), and if you really need additional height you can always just leave out some of the shelves that come with the set.
If you run out of wall and need to turn a corner, you can connect two lines of shelves by having both sets share one pole. I'm not sure how to describe it in words, but maybe this picture will illustrate well enough:
The circled pole is shared by a long set of shelves going off to the right of the picture, and by a three-foot shelf going to the left. A fun thing about this is that if I'm really, really slow and careful about it, the shelves on the left can be rotated around the pole to get the two large cacti in the corner out to be watered or whatever, and then swung back into place when they're done, thus leaving the corner still, in theory, usable.
Anyway. So this was the basic set-up I had in three different spots in the apartment, when we lived there. You can, if you are so inclined, try to suspend shop lights from underneath each shelf, but it's easier to just lay the shop lights on top of each shelf, pointing downward through the shelf they're resting on to light the plantsbelow. In some cases, I took advantage of that by placing small cuttings on the back of the shop lights, using the light above the plants for intense illumination and the light below them for bottom heat. It worked better for some things than for others, of course, but when it worked, it worked amazingly well.
The lights can then all be plugged into power strips, and the power strips placed on timers, to turn on sets of lights all at once.
One bad thing about the shelves is that it can be hard to get smaller pots to balance properly: you have to place a three-inch pot pretty carefully on wires that are an inch apart. I eventually resorted to getting some flat plastic (acrylic? polycarbonate?) sheets to lay down on top. They don't have to be especially strong, just flat. The air circulation suffers, but you have less dirt raining down on the floor, which is a plus.
It's also very easy for plants to fall over the back edge of a shelf, so I find it works best when I have one of these up against a wall, with the lights in back. Though putting them close to, but not touching, windows did work in the apartment in a few spots, and sometimes you have to do what you have to do.
What does a set-up like all this cost? Well, say you're going to buy two sets of 6-foot tall, 4-foot wide3 wire storage units and connect the fifteen shelves you get from that as far as they'll go, and light the backs of every shelf you can light the back of. Target often has these units available for about $60 each,4 so that's $120, and then if you're setting up like in my amateurish sketch above, you can light nine of the shelves (the very lowest one is too close to the floor to get any plants under, so there's no point in lighting it). That means nine shop lights and eighteen fluorescent bulbs. Figure $10 each for shop lights, and figure a box of twelve cool white bulbs costs $25 and a box of twelve warm white bulbs costs $35, and that a light timer can be had for $4 and a power strip costs $8:
$120 shelving units
$90 shop lights
$25 warm white bulbs
$35 cool white bulbs
$24 power strips
+$12 light timers
And what have you gotten for the $306? Well, you have ten shelves plants can go on, plus two sections of floor underneath the shelves where plants could also go. Each shelf is roughly 1.5 x 4 feet, or 6 square feet, so that gives you 72 square feet of space, except that the shop lights take up about (9*4*0.4) 14.4 square feet of that so you're really only getting (72-14.4) 57.6 square feet of space.5 And then that's only a net gain of (57.6-18) 39.6 square feet, because the whole set-up takes up 18 square feet of floor space that were there previously.
So 39.6 new square feet of growing space for $306: it's $7.73 per square foot. Pricey, but: all the new space, plus the floor area it takes up, is well-lit, higher-humidity (because the plants are closer together) space with good air circulation (wire doesn't block airflow), it's vastly cheaper than the equivalent 6'x6' greenhouse or room addition would be, you won't have to buy fluorescent bulbs for a while, the heights of the shelves can be adjusted as plants grow, and it doesn't add to your heating bill as dramatically as adding a room would. (It does use some additional electricity, but not really so much that you'd notice a difference unless you get really crazy with it.)
I was getting, on average, about 12-18 plants per shelf back in the apartment, so this would be space for approximately 135 plants, or more than that if you pick up more 3- and 4-inch plants like I recommended.
Set up another three units like this in another three rooms, and you have (57.6*4) 230 square feet of plant-growing space plus another 40 square feet of bottom-heat propagation space, room for 540 plants, and you've spent about $1224. The best part of this is that you can buy new shelves one unit at a time, so it's $1224, but in lots of little chunks over a long period. Unless you're really getting serious about propagation, or planning to buy a very large number of plants all at once, you can spend the cash in dribs and drabs, which makes it all sort of affordable. Or at least the kind of expensive you don't notice while it's happening.
The shelves are also moderately good bookshelves or aquarium stands,6 if you change your mind later and decide that you'd rather not keep so many plants. I mean, they're a decent long-term investment on their own.
So now you know how I crammed them all in. Is it an example to be emulated?7 I suppose depends on your priorities.
1 A lot of people will advise you to change bulbs after a year, even if they've not burnt-out. I know this is something the hard-core, competitive African violet growers do, for example. It is unquestionably the case that light output of fluorescent lights drops over time, and I can definitely see how this might become relevant if one were trying to create very standardized, uniform plants, or if one were trying to grow plants with very exacting light requirements. I don't worry about it so much, personally, because as I mentioned, fluorescent bulbs are not cheap. Also, the sites recommending this never really say what you're supposed to do with a whole bunch of dim, year-old fluorescent bulbs.
2 One recommendation I've seen, that I do like, is to mix one cool white (more blue) bulb with one warm white (more red) in each fixture. I honestly don't think the plants care, but the resulting color of light is a little more natural. Also, if you're worried about the red/blue wavelengths thing, mixing warm and cool bulbs would be a good way to feel like you're doing something about this without going bankrupt or turning your home lavender. I don't personally mix warm and cool lights in all of my light fixtures, because, again, I don't think the plants care that much, but in the cases where I have mixed the colors, I like the color of the light better, personally.
3 In most cases, the depth of the shelves is 18 inches, though other sizes are available. It really doesn't matter as long as you're careful not to buy different depths. You can mix three-foot-wide shelves with four-foot-wide shelves easily enough, and if you plan it properly you can mix different heights, too. But depths you have to match up correctly.
4 (though not always: right now their web site says $150: that's not typical, or even heard of, in my experience. The website's price structure is clearly different from that of the brick and mortar stores.)
5 Plus the backs of six of those shop lights could be used as bottom-heat, top-light propagation areas, so that's (6*4*0.4) 9.6 square feet of propagation area, in theory.
6 Mine were originally used as bookshelves; the plants didn't begin to crowd out the books until I'd had the shelves for eight years, and by then a lot of the books had moved on anyway. I'm not 100% certain about using them as aquarium stands: I forget exactly what the maximum weight capacity is supposed to be. Enough to have them full of books, in any case. They should certainly be adequate for a ten-gallon aquarium full of water, or a twenty-gallon terrarium, on each shelf. One minor drawback: the wires do bounce a little bit when heavy things are dropped on them, so they may not be quite as stable as you'd want: that could probably be dealt with by adding a sheet of plastic or a piece of plywood or something. Also, shop lights don't have quite as many alternate applications as the shelves themselves do, so you would still be stuck with those. But your shop, if you have a shop, would be blindingly bright.
7 No. It is probably not.