I love giving advice on how to get things for cheap or even free.
There are a variety of ways to get free or cheap houseplants. I’ll take them in order of increasing complexity. I’ll also be using Latin names of plants, you can Google them for more information. It’s a really good idea to research the sorts of plants you’re interested in as it could save you from all sorts of problems (like getting squirted with Euphorbia latex when you’re trying to take a “Cactus” cutting) and show you things you may well never have thought of (like growing other gesneriads, not just Saintpaulias or growing Aeoniums and Echeverias indoors instead of Sempervivums).
The following things may get you into legal difficulties but it depends where you do it:
- Stealing anything including plants, bits of plants, fruit or seed.
- Moving plants or bits of plants (seed is normally OK) across international borders, in your luggage or by mail. You may be able to get a permit.
- Removing plants, bits of plants, fruits or seeds from its habitat. You may be able to get a permit.
- Possessing certain types of plant (normally those that contain mind-altering drugs).
Getting People to Give You Plants
Most of us have friends and relatives who give us presents a couple of times a year anyway. You can just ask them for some type of plant. A lot of people don’t know their plants, so it’s a good idea to be specific. This is one place where knowing Latin names comes in handy. Common names aren’t always consistent. What’s a mother-in-law’s tongue in England is a snake plant in Canada (a man I met in Canada recently insisted that a Gasteria was a mother-in-law’s tongue!) but it’s Sanseveria trifasciata everywhere! If you’re at all fussy about what you want, it’s probably a good idea to write it down with some explanation like: “Aloe vareigata—not the same as Aloe vera! This has three rows of leaves with blotchy pale lines.”
This method is OK if you want something like a Ficus elastica but unless you have friends or relatives who propagate exotic plants, this probably won’t get you a Welwitchia bainsii.
Buying Plants at Garage Sales Etc.
There are places where people sell off things they don’t want anymore and sometimes that includes houseplants. Plants in these situations are likely to be cheap and easily grown common types. You may get lucky and find something rare.
Many cities have a Freecycle, an online group where you can get things people are giving away. Again, this will probably only get you fairly common, easily grown houseplants, but you may get lucky.
Buying Small Plants
You can often get small plants cheaply. Some plants never grow very big, in which case this isn’t really a bargain. Sometimes plants are only available in large sizes, so this doesn’t help. It’s good to look for plants that are outgrowing their pots, which should be good value for money.
Buying Annuals and Bedding Plants
Technically these are not the same thing but some plants are both. An annual is a plant that naturally grows from seed, flowers, produces seeds and dies in less than a year. A bedding plant is a plant that's planted in the garden in the spring and expected to die in the fall. The latter may well be non-hardy perennials that could be used as house plants. Certainly in Canada, garden centers often have signs up saying "Annuals" when what they really mean is "Bedding Plants".
These tend to be fairly cheap and some make good houseplants: Begonia, Impatiens, Pelagonium, Plectranthus etc. You really have to do some research with this one as real annuals won't do.
Growing From Cuttings
Basically you cut a bit off a plant and plant it. This can be used to propagate many plants and produces a clone of the original. The details of this vary with the type of plant and can get complicated. Most plants will grow from stem cuttings, some will grow from leaves, bits of leaves, tubercles (projections from the stem—mostly a cactus thing) inflorescence or roots. If something falls off easily and is still alive, it will probably grow. Some plants have special means of asexual reproduction, like the plantlets on Kalanchoes of the sub-genus Bryophyllum or in the inflorescences of Chlorophyllum. After Achinemes die down in the winter, you can get the rhizomes out of the pot and replant them, there should be more than were planted the previous spring. Succulents should be left for the cut to heal for a week or so before planting (although it’s a good idea to at least dip Euphorbias in cold water to stop the latex). Other plants can be stuck in water. Be careful with Euphorbias (extremely variable genus which includes the Pointsetta and a lot of cactus-like plants) as they can squirt caustic latex when cut. Pachypodium succulentum will grow from root cuttings but not stem cuttings but the very similar P. bispinosum is the other way round!
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Leaves from variegated plants (including Sedum ‘Rubrotinctum Aurea’) will often grow but produce normal plants.
Some vegetables can be used as cuttings, try ginger root, yam, sweet potato or pineapple (OK it’s a fruit!) tops. I’ve even seen an Asian store (in England) selling Caralluma edulis (a carrion flower) as a vegetable!
You can often persuade friends to give you cuttings of their plants.
Unfortunately, there are some plants (e.g. Aeonium nobile, most Astrophytums) that won’t grow from cuttings, at least not without messing up the original plant, usually by damaging its growing tip.
Layering is a variation on cuttings where you get a bit of stem to grow roots (usually by damaging it and putting potting compost round it—many sprawling plants will easily grow roots wherever their stems touch the compost) before cutting them off.
Most plants can be grown from seed (the exceptions are mostly abnormal forms and hybrids but ferns have spores instead of seeds—of course you can grow ferns from spores). You can usually get them to grow by placing them on damp potting compost and keeping them warm but the details vary (this is where research comes in). Seeds normally have reshuffled genetic material and often combine genes from two different plants. This may or may not be an advantage—it will allow you to produce new hybrids but you won’t normally be able to propagate a hybrid from seed (sometimes you can repeat the original cross and produce large numbers of similar plants—these are called F1 hybrids, but this doesn’t work for hybrids where one or both parents were themselves hybrids).
Sometimes you can get seed from your own plants (some will set lots of seeds with just a single plant, others will require two genetically different plants or a male and a female). If you cross-pollinate two different but related types of plant you will probably get hybrid seeds (sometimes this breaks down the anti self pollination mechanism and causes the seed parent to self pollinate). What will hybridize with what is a complicated matter (e.g. the tall desert cactus Pillosocereus will cross with the epiphytic cactus Heliocereus but you can’t (?) cross Astrophytum myriostigma with the very similar A. coahulence). It helps to know about flower and fruit structures if you want to pollinate flowers and collect the seeds—particularly with weird things like Euphorbias, orchids and Ascelpiads. You may also be able to get seeds from friends’ plants. You can get seeds out of most fruit (obviously has to be raw fruit and not seedless types). Exotic fruit (dates, kiwi fruit, dragon fruit etc.) will give you more exotic plants than apples or tomatoes. It might be a good idea to research what sort of plant the fruit comes from. A lot of fruit comes from trees, which may seem too large but most trees can be turned into bonsais (takes a fair bit of fiddling and a long time to get good ones).
You can also buy seeds from companies. Specialist companies tend to be cheaper and offer a larger variety. Non-specialist mixed cactus seed normally contains a small variety of mostly large, slow growing species. A specialist company may offer “globular cacti mixed” (small cacti that flower easily), “Mammillaria mixed” etc. and a huge choice of packets containing a single species, varieties or even from a particular location. This will often work out cheaper than buying plants and you will be able to obtain rare kinds (Welwitchia, Pseudolithos etc.).
You can buy plants on EBay but this can get complicated. You really have to know what you’re doing to recognize a bargain and there are laws about importing and exporting plants.
Join a Club
There are a number of organization for people who grow different types of plants. In my city, there are two African violet societies! This often allows members to sell, buy and swap seeds and plants. This is another good way to get rarer plants.
So now you can fill your home and greenhouse with all sorts of exotic plants without going bankrupt!