Friday, November 20, 2015

Building Raised Beds for Bulbs

Updated July, 2017

With a huge amount of advice and encouragement from the folks on the Pacific Bulb Society mail list, I decided to start building raised beds for my bulb collection. This post documents what I did, and what I've learned so far.

Summary. I am building one to two beds per year. So far I have four beds that have bulbs in them, and two new ones under construction (summer 2017). It's too early to judge, but things look encouraging. I think the soil mix I chose is working well, the bulbs seem happy, and the window screening around the beds is reducing the inflow of weeds (although not quite as much as I had hoped). The bulbs seem to grow from seed to bulb at about the same rate as they do in pots, and they look a lot more healthy (I get a lot of leaf dieback in pots, but almost none in the beds).

A Gladiolus hybrid bloomed in bed #1 in the first year. It looks reasonably happy. This was a blooming-sized bulb that I transplanted into the bed.

The details and more photos are below. I am very open to questions and suggestions. Please don't hesitate to post something in the comment section at the bottom!

Why raised beds? My main motivation was saving time. I have about 900 pots, and I'm adding another 200 or so new Moraea and Gladiolus crosses every year, plus some new species when I can find them. Even if I limit myself to one pot per cross, setting up all of those pots, and finding space for them, is a huge chore (not to mention expensive). Also, the collection is now so big that I can't repot it every three years, and the bulbs dwindle if they don't get repotted on time. If I add more pots I'll just make the situation worse.

I was desperate to find a better way to grow the bulbs. Then I saw photos of Fadjar Marta's rain lily beds in Indonesia, and was inspired (link).

A single one of my raised beds has about the same soil area as 300 pots, so if I do one new bed a year I can raise all of the year's new crosses in it, and gradually move some species over as well.

I'm hoping that the beds will need replanting less often than pots. We'll see.

The structure. I'll describe the second year's bed, since I think it's slightly improved over the first year. The bed is rectangular, 24 feet long and four feet wide (that's about 8m x 1.3m). It sits directly on the ground. The sides are pressure-treated lumber, ten inches high (a 2x4 on top of a 2x6). Quarter-inch hardware cloth was nailed to the bottom, and I also added a layer of landscape fabric under that to keep bindweed from growing up into the bed (a problem with the first year's bed).

This is bed #1. The wooden frame is finished, and the hardware cloth has been attached to the bottom.

The sides of bed #1 are two 2x4s stacked vertically. I used galvanized mending plates to connect the boards together. As you may notice, I used both chicken wire and hardware cloth under the first bed. This was overkill. I started with chicken wire, then realized the holes in it were too large. I was too lazy to un-nail the chicken wire, so I added a layer of hardware cloth under it. No digging animal will be able to penetrate this fortress of wire.

The bed is enclosed in a rectangular frame five feet high (about 1.7m). The frame is made of rigid electrical conduit, bent 90 degrees at the top and screwed together at the center over the bed. Bending conduit is fun (seriously; I like this stuff).  I attached wooden strips to the top of the conduit. The whole thing turned out surprisingly rigid, and has withstood strong winter wind.

This is bed #2. In the first bed, I used fence posts to hold up the roof. In the second bed, I used rigid electrical conduit. The conduit was bent over at the top and screwed together. I then attached strips of wood above the conduit, secured with pipe straps.

Here's another view of the wooden frame on top of the conduit in bed #2. Bed #1 is in the background. The shade cloth has sagged in the last year.

There's a roof of shade cloth over the bed, and the sides are enclosed with vinyl window screening (you can buy it in big rolls that are five feet wide). The shade cloth and screen are stapled to the wooden frame at the top.

Here's bed #1 almost finished. I'm stapling shade cloth to the top of it.

Bed #2 is complete. The wooden frame at the top has shade cloth stapled to it, and I've also stapled vinyl window screen along the top.

In the first year's bed, I stapled the bottom of the window screen to free-standing strips of wood (2" x 1"). The weight of the wood holds the screen in place, and when I want to open up the sides of the bed, I just lift up the wood. The problem with this arrangement is that the staples gradually tear through the screen.

In bed #2, I screwed the wooden strips to the lower frame, and hold the window screen in place with binder clips that fit over the wooden strips. I also clip the screen to the conduit. The binder clips are easy to buy in a stationery store. Unfortunately, I have to use a lot of clips (every three feet or so), or they pop off in heavy wind and the screen blows all over the place.

Seams between sections of window screen are hand-sewn together with nylon thread. This is easier than it sounds.

So far, the screen has been enough to keep rats and squirrels out of the beds. It helps that we have two feral cats.

The soil. I agonized over this. Rocky Mountain gardening guru Bob Nold argued persuasively for pure sand and gravel, but I was too cowardly. So I settled on equal parts sand, pea gravel, and planting mix, delivered by a local supply company. I got a total of three cubic yards of soil (about three cubic meters), enough to fill the bed with half a yard or so left over for other uses.

That's a lot of soil. If you make a bed like this yourself, I recommend renting a Bobcat or other front loader to move the soil. I failed to do that, and had a very nice workout with my wheelbarrow one weekend. All weekend long.

The soil is supplemented with a fairly generous supply of complete fertilizer (about one tablespoon [15 ml] of fertilizer per 2 gallons [7.5 liters] of soil).

I used redwood bender board to divide the bed into rows eight inches wide. That allows for about 300 8" x 7" planting spaces per bed. I did not put bender board between the bulbs in each row. That means they will eventually spread and mingle, but since I'm dealing mostly with hybrids I don't really mind. For species, I alternate genera in a row so I can tell them apart when dormant.

Here's the interior of bed #1, showing the bender board that separates rows of bulbs. Cut sections of vinyl window blind are used as plant tags.

Since the window screening seems to be keeping rodents out, I have not bothered putting  plastic chicken wire over the soil. But that was my original plan.

The results. So far, so good. The plants seem happy, with much less leaf dieback than I see in pots. Blooming was prolific in the first two beds in winter 2016-7. Here's a shot of bed #1:

I had hoped that the window screen would keep weed seeds out of the beds, and so far that's a partial success. The number of weeds inside the beds is a lot lower than outside, but there are more weeds than I hoped. Tiny airborne seeds (like those from dandelions) seem to slip through the screen easily, and I bet they are falling through the shade cloth on the top as well. Larger seeds, like the sharp "stickers" from wild oats, poke partway through the screen and gradually work their way in. The screening has helped, but I have to do a lot more weeding than I wanted to.

The window screening helps to reduce weeds, but some seeds do blow through. This is the typical weed density in bed #1 (the one that has been in place for 18 months). If you look closely, you'll see at least a dozen definite weeds in this photo, plus some thready leaves that might be weeds or might be second-year bulb seedlings.

The worst densities of weeds are along the edges of the bed. 

Here's the typical density of weeds outside the beds. So the screening helps, but it's not perfect.

I am very happy with the gravel in the soil mix. I had worried that it would pin down the little bulb sprouts, but since the bed is only 1/3 gravel, the leaves seem to be able to work their way up through it. The value of the gravel is that it resists erosion. Rain tends to drip down through the shade cloth in a stream that could easily wash away the soil underneath, but the gravel resists that. It seems to do a very good job of keeping everything in place.

The soil level is gradually declining in the older beds, presumably because the organic part of the mix is breaking down. So far this hasn't bothered the bulbs, but I hear it is a common problem in raised beds, and I worry that I should do something about it. I am open to suggestions. My goal is to keep the beds going without re-digging for as long as I can. Any advice?


  1. Mike I am so impressed with your growing setup. If I had precious surplus seeds I would want to send them to you because you clearly take great care with your bulb seeds. It looks like your investment of time and materials will pay off for years to come, not just for your own growing but for all those who learn from your blog post. Thank you.

    (PS: I did not harvest seed this past year but will in future.)

    1. Thanks, Gastil! I really appreciate the kind words.


  2. Talk about thorough! I hope the bulbs reward you for all of your hard work.
    I have a small bed that I have grown vegetables in but I have a hard time keeping it watered and I plan to convert it to a bulb bed over the next year. I am in Santa Barbara, California. Where is your place?
    Jim Foster

    1. Hi, Jim. I'm in San Jose, CA. It's a bit cooler in winter here than the marvelous climate in your area.


  3. It is not a secret, that the quality of the air in the house is often 2 to 5 times worse, and sometimes more than a hundred times worse, as compared to outdoor air, according to the U.S. Environmental Protection Agency. Actually a LEED home method was created to reduce exposure of pollutants and toxins in order to enhance fresh indoors air. Geoff Symons