Luffas are a challenge to grow in short-season areas, but if you’re interested in trying, read on. Photo: naturallivingideas.com
Par Larry Hodgson
Most people have seen luffa sponges, widely used as a scrubbing tool in kitchens and for exfoliating in the shower, but many seem to believe they grow under the sea. They’re confusing luffa sponges with the true sponge, which is a multicelled aquatic immobile animal, harvested and dried for retail sale.
The luffa sponge is instead the dried inside of a fruit that grows on a climbing plant in the gourd family (Cucurbitaceae). There are two species commonly grown for that purpose: the angled or ridged luffa (Luffa acutangula), which has a distinctly ridged fruit, and smooth luffa (L. aegypitiaca), with a smooth skin and in fact, looks much like a cucumber. They are also called vegetable gourds or dishrag gourds.
Another thing most of us don’t know about luffas is that, when harvested immature, as you would a cucumber, the gourds are edible and are popular vegetables in many Asiatic cuisines.
Growing Luffas Under Cool Conditions
A reader recently asked me how to succeed with luffas in her hardiness zone 4 climate. She’d already failed twice. I instead recommended that she grow something else … but then promised I’d write about growing luffas in a short-season climate in my blog. Honestly, I don’t recommend this, but it can be done. So, if you’re willing to put some effort into it, here’s how.
In a sense, luffas no more difficult to grow than cucumbers, which they resemble in so many ways, but they do need a very long growing season (about 200 days) and constantly warm temperatures to produce a mature gourd you could harvest for scrubbing. That makes them difficult to grow in colder climates, where the entire growing season can be less than 120 days and nights are likely to dip below 50˚F (10˚C) anytime between planting out and late fall. In hardiness zones 7 and above, growing them ought to be quite feasible, but in zones 6 and below … it’s going to be tough going.
The main secret is that you’ll likely have to grow the plants “under glass” (not that anyone much uses a true glassed-in structure anymore, but rather transparent plastic sheeting). Not necessarily a formal greenhouse, but something like a large teepee or head-high tunnel would do. The idea is to open the plastic greenhouse during the day to let out heat (except on the coolest days) and close it on any nights when temperatures will drop below 60˚F (15˚C) to keep in the heat. (The critical temperature is actually 50˚F (10˚C), but why take a chance?) Even one night below 50˚F (10˚C) can stop the plant cold and it can take a month to recuperate. At 40˚F (5˚C), it will likely die. So, keeping the plant under wraps, plus an earlier than usual harvest, should get you through.
I managed to grow luffas successfully only twice, decades back when I was a younger, much less laidback gardener, out for a challenge. I’ve since discovered that I no longer need to prove my garden mettle by forcing poorly adapted plants to bend to my needs. Hey, if I want a luffa sponge, I can go out and buy one!
So, here I’ll share what I know and if you want to take up the challenge, that’s up to you. But I do recommend trying something a bit easier if you live in a short-summer area, like such luffa relatives as cucumbers, cucamelons or squash.
Step by Step
Here’s what to do to succeed with luffas in a cold climate.
- Start with fresh seed, available from various online sources.
- Begin 8 weeks before the date you expect to be able to plant it outdoors (usually about 7 to 14 days after the last frost date). That would be mid-June for me, so I would sow the seeds in mid-April. If you sow too early, the plants become overgrown and won’t react well to transplanting.
- Soak the seeds overnight in a thermos of tepid water or nick the edge of the seed with a nail clipper to stimulate faster germination.
- Pre-moisten your sowing mix (any commercial seed-starter or houseplant mix will do) with tepid water until it is humid, but not soggy.
- Fill a large “peat pot” (these days, many are actually made with coir or cow pats) or newspaper pot with mix. That way you’ll be able to transplant the root ball intact come summer. You never want to disturb the root ball of a luffa, as that will set it back … and in a short season, you can’t afford any delays.
- Sow 2 or 3 seeds per pot at a depth of ¾ inch (2 cm).
- Cover with a clear plastic dome or bag to maintain high humidity and even temperatures.
- Place on a heating mat. I found this made a huge difference in germination. Seeds sprouted faster (within a week) and almost all came up.
- After germination, remove the plastic covering.
- Place under lights or in a sunny, warm window. Never put luffas anywhere nights are cool.
- If more than one seedling appears per pot, cut off the extra one.
- Water as needed to keep the growing mix a bit moist, adding fertilizer to the water every 10 days or so.
- The plants will try to climb, but you don’t want them to hook onto anything fixed, like a window screen, so either supply a short trellis you can move with them or bend them a bit so they grow sideways.
- Around the last frost date, prepare the soil in the planting area (it should be in full sun, ideally with no shade whatsoever) by mixing a few handfuls of compost. You can also grow luffas in a large tub if you prefer.
- It can be wise to put down black plastic mulch over the growing area to further warm up the soil.
- Cover with a clear plastic greenhouse structure of some sort.
- Install some sort of strong trellis or support inside: perhaps the structure of your greenhouse can be used or an extra solid tomato cage. (I grew mine up a chain-link fence). You could also allow the plant to grow along the ground, although that will likely give curved fruit if they touch the soil.
- When the air really is warm both day and night inside the greenhouse (you’ll likely want to keep a thermometer inside to check), plant out carefully without disturbing the roots at about 18 to 36 inches (45 to 90 cm) apart.
- As mentioned earlier in the article, keep the greenhouse closed on cool nights to trap heat, but open during the day unless temperatures are very cool.
- Water deeply and often. Never let the plant suffer from drought.
- You’ll probably have to control the fast-growing vines, redirecting them back towards your trellis. Otherwise, they’ll easily reach 10 feet (3 m) tall. In tropical climates, they grow to 3 times that!
- Much like cucumber flowers, there’ll be male flowers first (they grow in clusters), but when female flowers finally appear (easily recognized by the long gourd-shaped ovary at its base), it’s important the greenhouse be open during the day so pollinating insects can do their job.
- You can harvest the gourds when they’re 3 to 6 inches (7 to 15 cm) in length for use as vegetables if that is your choice. Any longer and they become fibrous and unpalatable.
- Keep up the “greenhouse conditions” as fall temperatures arrive. Remember, you’re trying to extend the season as long as possible.
- Theoretically, you should wait until the gourds start to turn brown, thus showing they’re full mature, before harvesting, but that’s unlikely in a cool climate. They probably won’t be nearly as large as ones grown under tropical conditions either. Instead, when they stop getting any bigger, feel a bit tougher when you squeeze them and nights outdoors are getting seriously cold and you’re no longer certain the sun’s heat will be enough to maintain warm temperatures, harvest them.
- Peel off the green outside layer, shake the seeds loose and voilà: a perfectly usable luffa gourd.
So, you can grow luffa in a cold or short-season climate … but are you really willing to put all that much effort into it?