Growing Melons in Sub Irrigated Planters (SIPs)

These melons grew on our roof a few years back and they were little rock stars. People couldn't believe how happy they were, hanging by their sturdy ropey threads. Melons are mostly water and they love sub irrigation, greedily drinking the reservoirs dry by the time they reach this size.

I seeded our melons this week, happily a day before Chicago became a high-wind inferno with temps around 97 yesterday and more of the same over the next two days. We have five selections this year, all thanks mostly to Debbie swapping me some nice varieties in our seed swap: 

Mexican sour gherkin

   Japanese icebox

   Korean ginka

   Tigger

 Golden midget

I promised myself this year that earlier in the season I'd switch out the SIPs that have been growing greens since March. Often I let them go to seed and we love to make seed, but the lazy (and late) gardener knows these SIPs can be quickly dispatched and replanted. 

Pull off the shower cap, pull out the greens and remove the fertilizer (sending all down to the compost bin)...

...and top up with potting mix and fresh fertilizer. Ready, boom, for five types of melon.

 

I even re-used the plastic shower caps with multiple holes. You can plant more greens than melons in a 5-gal SIP. We plant four melon seeds and hope for good germination, culling to leave the two strongest seedlings. For all planting in a 5-gal SIP, cut in half the amount you're instructed to plant in a standard-sized Earthbox (the link has a pdf showing how many of most veggies will grow well).

Here's a friend getting ready to enjoy one of the 2011 Golden Midgets. Come back, JT (and Alex too), when this year's melons ripen!

Testing and Amending Coir

I'm not giving up on coir yet......Our neighbor, Carol, has been growing greens successfully in 2 bucket SIPs using coir. That suggests to me that coir will wick water in the same way that peat does. One difference was that she bought her coir from a local source, Brew and Grow. The coir they sell is roughly double the cost of the stuff we bought from Rolanka.

I like beurmann's idea of sending out a sample to be tested for nutrient levels and excess salts. He left links to several local testing companies and generously offered to split the cost. The first test is on me, if this gets expensive I'd be happy to take him (you?) up on it.

One the same subject, thanks, too, to our friends at Homegrown Evolution for pointing me to a great, cheap testing lab for any kind of garden soil -- UMass Soil Lab. I tried calling them to ask if testing for excessive salts in coir was possible and was asked to leave a message in a full voicemail box.

I'm a little confused by what kind of test I need to have done. Take a look at one company's menu of testing options. Does coir even count as "garden soil"? A phone call to one of testing companies might clear things up.

:::

In any case, it looks like I'll need to amend my coir with garden gypsum and epsom salts to get a soilless mix that transfers nutrients to my plants. From "tapla" at the GardenWeb Container forum -

Sphagnum peat and coir have nearly identical water retention curves. They both retain about 90-95% of their volume in water at saturation and release it over approximately the same curve until they both lock water up so tightly it's unavailable for plant uptake at about 30-33% saturation. Coir actually has less loft than sphagnum peat, and therefore, less aeration. Because of this propensity, coir should be used in mixes at lower %s than peat. Because of the tendency to compact, in the greenhouse industry coir is primarily used in containers in sub-irrigation (bottom-watering) situations. Many sources produce coir that is very high in soluble salts, so this can also be an issue.
Using coir as the primary component of soils virtually eliminates the reasonable use of lime or dolomitic lime as a Ca source because of coir's high pH (6+). Gypsum should be used as a Ca source, which will also help eliminate problems associated with coir's low S content. All coir products are very high in K, very low in Ca, and have a potentially high Mn content, which can cause antagonistic deficiencies and interfere with the uptake of Fe.

He, "tapla", gives some specific directions on how to amend the coir later in the same thread -

OK - I like peat much better, but of course it's your soil. ;o) Add 1 level tbsp of gypsum per gallon of soil or a skinny 1/2 cup per cu ft. Because you should use gypsum as a Ca source in coir-based soils, you'll need to use MgSO4 (Epsom salts) as a source of Mg, and so the Ca:Mg ratio isn't so skewed that you create a Ca-induced (antagonistic) Mg deficiency. Use 1/8-1/4 tsp per gallon of fertilizer solution every time you fertilize, or every other week if you're attempting to insure nutrients via organic soil amendments.

More information that suggests that adding gypsum is the way to go -

Coconut coir, a by-product of the coconut industry, has been promoted as an alternative to peat moss in soil-less media. Sphagnum peat moss has long been a standard component of soil-less media, but some people have expressed concern that it is a non-renewable resource. Although it does not appear that world peat resources will be in short supply for a very long time [nevermind the habitat loss and release of sequestered carbon, ed.] , coconut coir may have characteristics that make it a useful component of soil-less media mixes. Coir has been considered to promote excellent plant growth but there are few rigorous studies that have compared it with peat moss control plants. However, ten years ago, Meerow (1994) found that growth of Ixora coccine was significantly reduced compared to growth in a sphagnum peat moss control. Vavrina (1996) found that there were no adverse effects of coir to tomato and pepper transplants, but a subsequent study in the same lab (Arenas et al., 2002) found that media with more than 50% coir had reduced growth compared to peat-grown control plants. They suggested that a high N immobilization by microorganisms and a high C:N ratio in the coir may have caused the reduced growth. Lopez-Galarza (2002) found that root development of strawberry plants grown in peat moss was better than in coir in some, but not all, studies. Handreck and Black (2002), in a comprehensive textbook on soil-less media, review the chemical and physical properties of coir dust that are being sold in Australia. They indicate that since all coir products have extremely high K contents and low Calcium contents, it is critical to add a source of Ca to improve plant calcium uptake. Since the pH is already close to 6, liming materials cannot be used because they would increase the pH above optimum. Handreck and Black says that “Therefore, all coir-based media must be amended with gypsum, which also overcomes their low sulfur status.” [emph. added] Ma and Nichols (2004) recently reported that the problems with coir extend beyond its high salinity. Their data indicate that high concentrations of phenolic compounds in fresh coir are at least partly responsible for the growth reductions observed in other studies. Several studies at the USU Crop Physiology Laboratory indicated that monocots grown in coconut coir were extremely chlorotic and stunted. The objective of this study was to see if there are differences among plant species and types of coconut coir compared to growth in sphagnum peat moss.

Sub-Irrigated Chicago Rooftop Garden: New Approaches for 2010

We're making a few changes this year, large and small, to speed multiple SIP planting and help preserve diminishing peat bogs.

Using a large rubber band to secure the 5-gal SIP shower cap
Sounds obvious, but in the past we've used string or the more expensive zip ties. We'll see if rubber bands hold up under all that UV, though the position of these under the bucket lip should mean the sun won't bake them to smithereens. You need nimble fingers to use them, though.

(And kudos to the marketing person who named these rubber bands.)




Potting Mix: peat+perlite vs. coir+perlite

We want to move away from peat moss, which develops over millenia and, when harvested, releases massive amounts of carbon dioxide into the atmosphere.

We're going to make this experiment as exacting as possible, planting two peppers, two tomatoes, and two sets of greens side-by-side, one each in coir/perlite and the other in our old peat/perlite mix (of undetermined exact specifications).

Bruce's recipe is: 70% (by reconstituted volume) coir and 30% perlite.

We found a relatively inexpensive (including shipping) source for large blocks of coir at Rolanka. We've been buying the 5:1 compressed blocks. Four come bundled together, costing $58 delivered to Chicago. Each of the blocks, reconstituted with 6 gallons of water and combined with 3 gallons of perlite (from Anton's Nursery in Evanston, $20 for a 4 cubic foot/30 gallon bag or at Home Depot for $2/gallon), makes enough potting mix to fill three 5-gallon bucket planters (3 cubic feet of mix).

All those numbers can be summed up in one sentence: The coir/perlite mix is $5.50/cubic foot, about the same price as the peat based potting mix we've been using.


Cutting out exact-sized plastic rounds for the "shower caps"
Sounds minor, but I formerly used an old form to score garbage bags and cut out shower cap circles. They were a little large and I always ended up trimming the extra skirt from the top of my SIPs. And yes the results looked raggedy.

I discovered the 16" diameter recycled Olive Garden salad bowl (garbage picking at that graduation party last year was a boon) creates a perfectly sized round for the 5-gal bucket SIP. You can cut a plastic circle out of anything waterproof--a soil bag, whatever. I like garbage bags because they're thin and flexible.





Water fill tubes
One of our local readers last year brought us a roll of polyethylene drip irrigation tubing, which we'll cut and use for fill tubes on the new SIP run this year. Generous person whose name we have misplaced: thank you!

We'll keep you updated on the results of our changes. If you're making any, let us know.