Caffeine: A Powerful Organic Insecticide


The coffee plant (Coffea arabica), a common houseplant, produces its own insecticide: caffeine. Source:

Did you know that caffeine is an insecticide? Moreover, that the coffee plant (Coffea arabica and others) produces it in order to protect itself from predatory insects? When under attack by unwanted invertebrates, moreover, the coffee plant increases the dose of caffeine, often producing enough to kill the intruder.

Caffeine extracts applied to various insects (milkweed bugs, caterpillars, mosquito larvae, etc.) cause agitation, reduce appetite, inhibit reproduction, and can even lead to death. Caffeine-treated mosquito larvae, for example, become so poorly coordinated that they can no longer swim and end up drowning.

Several companies are working on deriving an organic pesticide from caffeine and other similar substances.

Note that theine, produced by the tea plant (Camellia sinensis) and present in tea, is actually just caffeine: the two are chemically indistinguishable. And the caffeine/theine in tea plants serves the same purpose: to repel or kill insects that attack the plant. Theobromine, present in the cacao tree (Theobroma cacao), plays a similar role. Both caffeine and theobromine are xanthine alkaloids.

Are Caffeine and Theobromine Toxic to Humans?


Café in reasonable quantities is harmless and even beneficial to most adults. Source:

It’s said that it’s the dose that makes the poison and so is it with caffeine and theobromine: the amount present in a cup of coffee, tea or hot chocolate (or a glass of Coca Cola or Pepsi) is insufficient to kill a human. Moreover, some adults drink three or four cups a day without suffering any major sequel. As a result, most people think of caffeine and theobromine as being rather innocuous. Our body simply digests these alkaloids as with so many other products we ingest.

In addition, several studies indicate that coffee, tea and yes, even chocolate can be beneficial for your health, at least in case of adults. Drinking one or two coffees a day seems to help protect against Parkinson’s disease, diabetes and various liver diseases including cancer, improves cognitive function and reduces the risk of depression. Note that we don’t know why coffee seems good for our health and that these benefits don’t necessarily come from caffeine: coffee contains about 1,500 chemicals and only very few have been studied.

However, caffeine isn’t always as innocuous as we like to think. The amount of caffeine found in energy drinks and diet pills is much greater than in a typical cup of coffee or tea (there are about 100 ml of caffeine in the average cup of coffee, but 300 ml in a typical energy drink) and either product can lead to an overdose and even death, especially in adolescents, if abused.

There is also the risk of developing a physical dependence on caffeine. As little as one cup of coffee or two of tea a day (about 100 ml of caffeine) can lead to physical dependence and, if you stop drinking them, sometimes serious withdrawal symptoms. It’s estimated that nearly one quarter of adults worldwide are “hooked” on caffeine.

Very Toxic to Animals

20171129C .jpg

You should never give coffee or tea to pets. Source:

Caffeine is much more harmful to pets than to humans. Don’t ever let them drink coffee, tea or hot chocolate or eat coffee grains or chocolate bars. Even chewing a leaf or two on from a coffee plant, found in many homes as a houseplant, can send a cat to the vet’s.

What About Coffee Grounds?

The Internet is full of websites extolling the merits of coffee grounds as a handy-dandy insect repellant for the garden, claiming that if you apply them to the base of plants, it will keep undesirable insects away. Unfortunately, no serious study has ever found any truth to that, and for good reason. Because there is no longer enough caffeine left in coffee grounds to repel insects: you have already drunk the insecticidal part!20171129A

Edible Houseplants

Coffee fruit - Coffea arabica

A coffee plant (Coffea arabica) will produce it’s colorful “cherries” indoors.

Question: Are there any houseplants that are both edible and attractive?

Clecio Turgeon

Answer: There are many tropical plants that are both easy to grow indoors and give us something to nibble on or to add to our recipes… but you won’t find many among the most common houseplants we grow. Most “everyday houseplants” are either not considered edible or are even poisonous. The latter group includes such popular plants as philodendrons, dieffenbachias, oleanders and most euphorbias. You don’t want to eat those!

What follows is a description of some the more interesting edible houseplants.

A Growing microgreens on plastic white cup

Micro-greens aren’t really houseplants.

Plants Dropped From the List

I eliminated from the get-go certain plants that I just don’t consider to be houseplants. For example, I didn’t include most of the herbs brought indoors in the fall to grow over the winter, as in my opinion they are not really houseplants and in fact really struggle to survive indoors. You really couldn’t grow them indoors all year.

Nor did I include herbs and vegetables that are sown indoors with a view towards a quick harvest of fresh foliage: sprouts, micro-greens and baby vegetables, for example. Again, in my book, they may be indoor edibles, but they’re not really houseplants. Likewise rooted carrot tops, sprouted sweet potatoes or celery bases sitting in water. They just aren’t houseplants to me.

There are also a few poisonous plants that are edible only after they’re given some kind of special treatment, like cooking, soaking, pounding or being reduced into powder, such as taro (Calocasia esculenta) and variegated manioc (Manihot esculenta ‘Variegata’). I didn’t think it was a good idea to include potentially dangerous plants in a list of edible houseplants, as some readers might skip the “fine print”.

Everyday Houseplants That Are Edible

Here are the few common houseplants, ones readily found in almost any garden center, that just happen to be edible.


Calamondin orange (X Citrofortunella microcarpa)

Calamondin Orange (X Citrofortunella microcarpa, syn. X C. mitis)
This is the only citrus commonly offered as a houseplant. It is inevitably already in fruit when you buy it and you just need to give it good conditions (especially, strong light) for it to continue it bloom and produce abundantly. The fruits are very bitter, but they can be used in cooking, especially in the preparation of marmalades. For suggestions of other less widely available indoor citruses, see Indoor Fruits below.

Chinese Hibiscus (Hibiscus rosa-sinensis)
The flowers are edible and often used in herbal tea. Here’s an article about this plant: The Secrets to Growing a Hibiscus Indoors.

Coffee (Coffea arabica)
Young coffee plants, usually scarcely more than seedlings, can easily be found on the market, but may be 2 or 3 years from blooming… and 5 to 6 years before producing enough beans to make a cup of coffee. Occasionally you find more mature plants already producing their highly perfumed white flowers.

You can actually eat the sweet flesh of the coffee “cherries” that follow or simply clean, roast and grind up the “beans” (seeds) to make a delicious drink.


False shamrock (Oxalis triangularis)

False Shamrock (Oxalis triangularis, syn. O. regnellii)
The leaves of this popular houseplant can be purple or green, with or without a silvery or pink marking… and they are quite edible, with a sweet/sour taste. This comes from the oxalic acid they contain. However, oxalic acid becomes toxic if eaten raw in large quantities, so moderate your use. Or cook the leaves before use. Just to reassure you, remember that spinach, which we routinely eat, also contains oxalic acid and is also toxic if eaten raw in excessive quantities. As they say, the poison is in the dose: eating a few leaves will not harm you.

Ornamental Pepper (Capiscum annuum and others)
All peppers are edible, even the ones sold as ornamental plants. Be forewarned though that ornamental peppers are hot peppers, indeed, very hot peppers, generally stronger then jalapeños.

You may sometimes see them bearing the label “unfit for human consumption”, though. Why is that? It’s not because the fruit itself is poisonous, but because it was treated with an insecticide that is potentially harmful to humans. Organic gardeners will consider the fruits spoiled for life; others can wait a few weeks, then rinse the fruits before eating them. Both can harvest the seeds and grow them to produce fruits totally safe to eat in the second generation.


Ornamental pineapple (Ananas comosus cv)

Pineapple (Ananas comosus)
There are several varieties of ornamental pineapple, for example with reddish foliage, variegated leaves, colored fruit, etc. And all produce fruits which, although they’re often smaller than commercially grown pineapples, are still edible.

Besides ornamental varieties of pineapple, you can also buy a fresh pineapple and root its crown. And yes, it will eventually produce an edible fruit.


Lemony rose scented geranium (Pelargonium graveolens ‘Lady Plymouth’)

Scented Geranium (Pelargonium graveolens and others)
There are a multitude of varieties of scented geranium with an incredible array of scents: lemon, rose, coconut, apple. peach, strawberry, cloves, etc. In addition to rubbing the foliage to release their scent, you can use their leaves in cooking to impart a delicious aroma to your meal. Richters (Canada) offers an especially wide choice: more than 70 varieties of these highly perfumed plants!


Swiss cheese plant (Monstera deliciosa)

Swiss Cheese Plant or Monstera (Monstera deliciosa)
Often mistaken for a philodendron (which is a close relative), the monstera, with its huge, deeply-cut leaves, certainly makes an impressive houseplant. When it reaches maturity, which can take many years, it will flower indoors, producing a white inflorescence recalling a calla lily. And the flower is followed by a sweet-tasting fruit, which is the reason for the botanical epithet deliciosa. The fruit can take 11 to 12 months to mature, and doesn’t change color too visibly at maturity. So how do you know it’s ripe? When the green scales that cover it begin to drop off, it’s ready to eat.

Note that the entire plant, from its roots to its leaves to its immature fruits, is toxic. Only the mature fruit is edible.

Tea Plant (Camellia sinensis)
Yes, tea plants. although not yet as common as the other everyday houseplants presented here, are found more and more often in garden centers. Here is an article about how to grow one: Homegrown Tea in Your Teapot.

Indoor Fruits

There are hundreds of different tropical fruit trees, all of which could theoretically be grown indoors, but most won’t produce for decades, will become too large to make good houseplants or require really extreme growing conditions. Since they are unlikely to ever produce fruit in your home, I excluded them from my list.

In this group of “forbidden fruits”, you’ll find most of the tropical fruits that can be grown from seeds or pits harvested from the fruits you buy, such as avocados (Persea americana), mangos (Mangifera indica), and papayas (Papaya carica). Of course, if you look hard enough, you may be able to find dwarf varieties of these plants that will produce fruits indoors, but otherwise its best to consider most tropical fruits you grow from seed simply as foliage plants!

What follows are a few fruiting plants that are more suitable for growing in our homes and that really do make good edible houseplants.


Barbados cherry (Malphigia glabra)

Barbados Cherry (Malpighia glabra)
Pretty pink flowers, bright red cherrylike fruits on a small shrub that fits neatly into most home decors. What’s not to like?

Cacao Tree (Theobroma cacao)

A challenge to grow and not readily found on the market, a cacao tree can still produce cacao beans at home… if you turn your home into a hot and humid jungle year round.


Key lime (Citrusaurantiifolia) makes an easy-to-grow indoor citrus.

Citrus (Citrus spp., Microcitrus australasica and Fortunella spp.)
As mentioned in the article A Lemon or Orange Tree From Seed?, real lemon trees, orange trees, grapefruit trees, etc. are simply too large and too slow to produce to make good indoor fruit trees, unless you can find grafted dwarf varieties.

Other lesser-known citrus fruits, faster in growth and of a naturally smaller size, make much better indoor plants. This is particularly the case for the Meyer lemon (Citrus x meyeri) which, despite its name, is not a real lemon, the Key lime (C. x aurantiifolia) and the Australian finger lime (Microcitrus australasica). You can sow any one of these and have fruit 2 years later!

Kumquats (Fortunella spp.) too make excellent indoor fruit trees.

Common Fig (Ficus carica)
It prefers to pass its summer outdoors… and has the bad habit of losing most of its leaves during the winter, leading to a rather stark appearance, but the fig tree still quite readily produces figs indoors. Moreover, its foliage is edible too.


Dwarf banana

Dwarf Banana (Musa spp.)
Even a dwarf banana tree takes up a lot of space indoors (among the smallest cultivars are ‘Super Dwarf Cavendish’ and ‘Truly Tiny’) and also require a lot of heat, humidity and sun to produce fruit. Plus they may take years to produce bananas, but still, most will eventually do so if your conditions are right.

The pink banana (Musa velutina), with pink flowers and fruits, is another small-size edible banana you might like to try, but you’ll have to eat around its large seeds.


Dwarf pomegranate (Punica granatum ‘Nana’)

Dwarf Pomegranate (Punica granatum ‘Nana’)
This is a miniature version of the rather large pomegranate tree whose fruits are found in the supermarket. It forms a small to medium-sized shrub with orange flowers that will readily produce small but nevertheless edible fruits indoors. Even if you grow it from seed (it comes true to type), it will bear blooms and fruits in only a few years.

Natal Plum (Carissa macrocarpa)

This small thorny shrub with shiny leaves makes a good houseplant and readily produces white flowers and edible red fruits. It is sometimes used as bonsai. Both the stem and leaves, and even the sap, are poisonous. Only the ripe fruit is edible.


Passionfruit (Passiflora edulis)

Passionfruit (Passiflora edulis)
This vigorous climber will need a good trellis, but can produce its white flowers with a purple halo and its purple or yellow fruits (the color depends on the cultivar chosen) in a sunny spot indoors. There are plenty of other species of passionfruit that do well indoors, but only a few produce edible fruit.

Pitahaya or Dragon Fruit (Hylocereus undatus, H. polyrhizus, H. megalanthus and others)
These climbing cacti take up a lot of space, but bloom fairly easily when they reach maturity (after 5 or 6 years), producing enormous white fragrant nocturnal flowers followed by large red or yellow fruits with white flesh that is dotted with tiny black seeds. This is a good example of a plant you can grow to fruiting size from seeds harvested from fruit purchased in the supermarket. You just have to be patient!


Fishbone cactus (Epiphyllum anguliger)

I grow a smaller and closely related cactus, the fishbone cactus (Epiphyllum anguliger), with hanging flattened zigzag stems whose very fragrant nocturnal white flowers often give small edible green fruits… but it’s difficult to judge when they are ripe. It too takes years to begin to bloom, but once it starts, it will faithfully continue to do so.

Pixie Grape (Vitis x Pixie® Pinot Meunier)

A dwarf mutation of the Pinot Meunier grape vine which produces fruit all year on a small plant… and its leaves are edible too. It can be grown as a houseplant, but is also hardy outdoors.


Roselle (Hibiscus sabdariffa)

Roselle (Hibiscus sabadariffa)
This shrub with small yellow hibiscus flowers grows quickly from seed. In fact, you can treat is an annual if you wish. It produces red fruits often used in drinks and jellies.

Indoor Herbs and Spices

Herbs and spices flavor our meals and often have medicinal uses as well. I limited the choice here to varieties that really make decent houseplants.

Bayleaf (Laurus nobilis)
In my opinion, this is the only “classic” herb that grows well enough indoors to make a good houseplant. It will grow indoors for years, eventually forming a tall shrub if you don’t prune it. The leaves can simply be plucked and used fresh as needed.

Black Pepper (Piper nigrum)
This climbing plant produces smooth shiny leaves and long spikes of green berries that turn red at maturity and is not difficult to grow indoors if you can offer good humidity. The berries give black, white or red pepper, depending on the treatment you give them.


Ginger (Zingiber officinale)

Ginger (Zingiber officinale)
You can readily grow ginger from rhizomes purchased locally. Beware though that the rhizomes offered in many supermarkets were treated chemically or irradiated in order prevent them from sprouting. There is no use planting those! You need live rhizomes, with buds indicating they are ready to sprout. An Asian supermarket should have some.

Just push a section of rhizome into a pot of growing mix and water: a green rather bamboolike plant will soon start to sprout. Over time, the rhizome will spread and you can then harvest and eat any surplus. Don’t expect this plant to flower indoors, though: it almost never does.

Other spices in the ginger family also produce edible rhizomes and likewise make excellent houseplants: galanga (Alpinia galanga), turmeric (Cucurma longa) and cardamom (Elettaria cardamomum) are only a few examples.


Society garlic (Tulbaghia violacea)

Society Garlic (Tulbaghia violacea)
This is a bulbous plant with grasslike leaves and small pink trumpet flowers. The whole plant smells like garlic. If you use the edible leaves and flowers in your cooking, they’ll give the meal a garlicky scent, but without the bad breath that follows eating real garlic. The name society garlic come from the idea that you could safely eat it before attending polite society functions.


The variegated forme of Spanish thyme (Plectranthus amboinicus ‘Variegatus’) is probably more popular than the species.

Spanish Thyme or Cuban oregano (Plectranthus amboinicus)
This plant is neither a thyme (Thymus spp.) nor an oregano (Origanum spp.), but rather a tropical plant closely related to the coleus (Coleus scutellaroides, syn. Plectranthus scutellarioides). It’s a very popular herb in tropical countries where its thick leaves lend taste of oregano to cooked dishes. It’s very easy to grow.

Stevia or Sweetleaf (Stevia rebaudiana)
Increasingly popular for its sweet leaves that give dishes a sugary flavor without adding calories… and it makes a decent houseplant.

Indoor Vegetables

There aren’t many plants you could call vegetables that also make good houseplants. I could only think of the following two:


Malabar spinach (Basel alba ‘Rubra’)

Malabar Spinach (Basella alba)
An ornamental climber with mucilaginous leaves used to replace spinach, Malabar spinach is often grown in hot climates where real spinach doesn’t grow well. The species itself produces green stems and white flowers, but B. alba ‘Rubra’, perhaps even more commonly grown, has reddish stems and pink flowers. Both are very easy to grow.


Spineless nopal (Opuntia ficus-indica ‘Burbank Spineless’)

Nopal or Barbary Fig (Opuntia ficus-indica and others)
Many different opuntias are used as nopals, but Barbary fig is the most common one. This cactus with flattened pads does produce edible fruits called Barbary figs when grown outdoors in a hot, dry climate, but indoors it rarely blooms, let alone produces fruit. It made it onto my “edible houseplant list” by virtue of its edible pads.

Nopal is the name commonly used in Mexico for the pads treated as a vegetable. You’ll probably need several plants if you want to start harvest nopals, as the plant is very slow growing. You have to singe off the spines before you eat the pads… or use spineless (or nearly spineless) cultivars like ‘Burbank Spineless’.

This plant will need full sun to do well indoors. And yes, you can root a pad from the grocery store to start a new plant.

Where to Find Edible Houseplants?

Many of the plants above are not found in just any garden center, so here are few places where you might want to look for them on the Web.

For herbs and species, try Richters, a Canadian company that ships to the US and probably offers more choices of herbs than any other.

For unusual fruits and vegetables, try Flora Exotica, also a Canadian company that ships to the US, while Top Tropicals is an American company that ships to Canada and many other countries worldwide. Logee’s, in the US, is a good source for American readers, but no longer ships to Canada.

For European readers, try AlsaPlants. If you know of any other good mail-order sources of indoor edibles in Europe, let me know and I’ll add them to this text.

Bon appétit!

Homegrown Tea in Your Teapot?


Grow Your Own Tea Indoors!

20151117AThe tea plant (Camellia sinensis) is a tree native to subtropical Asia. Tea is grown commercially in many countries, including China, India, Kenya, Sri Lanka and Turkey and that’s not surprising: tea is the second most widely consumed beverage in the world. Only water beats it! But you don’t need to undertake a long voyage to see a living tea plant, because you can easily grow one on your windowsill.

Not the Same as the “Tea Tree”

Note that the plant we’re discussing here is commonly called tree plant, Camellia sinensis, and is from the tea family or Theaceae. It’s the one that gives us tea leaves and produces your favorite tea. The tea tree is one of various plants in the myrtle family from New Zealand and Australia, including Leptospermum scoparium and Melaleuca alternifolia, some used medicinally as “tea oil”. But they are very different plants.



Commerical tea plantation.

The tea plant can reach up to 55 feet (17 m) tall in the wild, but is extensively pruned to facilitate harvesting, which usually gives a shrub some 4 to 6 feet (1 or 2 m) in height. It produces small but pretty white flowers with yellow stamens, somewhat like small magnolias. It is a very close relative of the camellia (C. japonica), whose pink, red, or white flowers, often double, are much larger and more attractive. Still, if your tea plant ever blooms, you’ll certainly appreciate the show.

The tea we consume is derived from its leaves: according to the treatment given, the same leaves can give green tea, white tea, black tea, oolong tea, etc.

For gardeners in temperate climates, the tea plant can only be grown as a houseplant. Of course, you can put it outdoors for summer, but you’ll have to bring it back indoors before winter. There are a few select “hardy” strains that will survive in protected spots in the USDA hardiness zone 7 (AgCan zone 8), but in general, you’d have to live in a subtropical climate (zone 9) to be able to grow tea outdoors year round.


Tea plant in bloom

The tea plant can make a pretty foliage plant with its shiny dark green leaves with finely toothed margins… and if yours blooms, you’ll certainly appreciate the small white flowers, but it normally takes several years before a tea plant reaches blooming size, at least under typical home conditions. And if you harvest too diligently, regularly removing new growth, it may never bloom at all.


In the winter, give your tea plant a bright sunny spot and, if possible, cooler conditions, about 40 to 60˚F (5 to 15˚C), although it will grow fairly well enough at average indoor temperatures. During the summer, it will prefer a bit of protection from intense sun, perhaps a spot where it gets shade in the afternoon. You can grow it in full sun too, as long as you don’t let it bake in the brutal heat near a south window.

Pot up your tea plant into typical houseplant soil and water thoroughly when the soil is dry to the touch. Good air humidity is important during the winter, so a room humidifier can be a major asset. It prefers diluted but regular feedings, at about one quarter of the recommended rate, using the fertilizer of your choice (it’s not a picky feeder), from spring to fall. Avoid fertilizing in winter when the plant is essentially resting.

The tea plant prefers acidic soil (pH 6 to 6.5)… which is normally the pH of commercial potting mixes. On the other hand, tap and well water in many areas is very hard (alkaline), so over time the soil may tend to become too alkaline. A summer stay outdoors can therefore be helpful, as rainwater is soft and will help dissolve and flush out the lime that causes the problem. If not, repotting annually in late winter into fresh soil will help keep the pH in the right range.

You can multiply your tea plant by cuttings or seeds. Several seed companies offer tea seeds in their catalogs, notably Richters and Chiltern Seeds and sometimes tea plants are offered in local garden centers. If not, try visiting a herb specialist. And plants are relatively easy to find on the Internet, notably at Logees and Territorial Seed Company in the US and Flora Exotica in Canada.

Harvest Time!

To prepare green tea, simply pluck fresh leaves and infuse them in hot water. The plant will react to your pruning by growing new leaves. Just don’t harvest all the leaves at once or you’ll weaken your plant; instead, pick a cluster of leaves here and there. The harvest season will normally range from March to October. Removing leaves during the winter months is not a good idea.


Imagine making your own tea from fresh leaves!

Making green tea from your tea plant is simple enough: just harvest leaves and buds, chop them up, and let them steep in hot water. Black tea requires bruising the leaves so they turn brown, then letting them dry. Experiment to find how you best like to serve your homegrown tea!

Now for the bad news: you won’t be able to wow your neighbors by inviting them over for tea made from your tea plant, at least not all at the same time. A young plant will provide at most 1 or 2 cups a year, although once it is mature, you may be able to get a few cups every 2 months. It will take many plants − and good-sized ones at that! − to be able to drink fresh tea on a more daily basis!