From Kew to Your Front Room

I have my own personal time machine, and it's made out of a takeaway container and some moss. It's not as spacious as a TARDIS or as cool as a DeLorean, but popping the lid on my plastic prop box swiftly transports me back to the glasshouses at Kew Gardens circa the 80s and 90s. The warm, earthy fug that emits from a clear box full of tropical plant cuttings is my equivalent of Proust's madeleines: a smell that can deposit me straight back into my youthful trips to see tropical plants. Many of the things I saw at Kew I'd only read about in my plant bible of the time, The Houseplant Expert by Dr David Hessayon. As a child houseplant nut (school nickname: Botany), I was in heaven.

Living at the end of the Metropolitan line, my home was in easy travelling distance of Kew Gardens in London, and I visited many times as a child and teenager. That's me in the image above in the Waterlily House, in my late teens or early 20s (wish I still had that leather rucksack: still have the necklace). I'm in side profile, but I think you can still tell that I am in awe of what's around me. Above the ridiculously large pads of the Amazonian giant waterlily that fill the central pond are palms, aroids, ferns - a houseplant grower's equivalent of a fully packed chocolate box, full of all my favourite delights.

I don't get to visit Kew as often these days, but I love to try to emulate the smells of the fecund vegetation there by maintaining a small selection of prop boxes on the go at all times. Beyond packing a Proustian punch, it also allows me to produce lots of new houseplants.

What's a prop box?

A prop box - short for propagation box - is the place where you raise new plants to add to your collection, as an insurance policy against losses and to engage in swaps with other houseplant growers.

If you're a denizen of planstagram - the houseplant community on Instagram - you may imagine that prop boxes are a newfangled thing invented by Gen Z. Not so. People have been putting cuttings in boxes since glass was invented and before. For instance Romans used lapis specularis (transparent sheets of crystallised gypsum) to create simple greenhouses for raising melons.

What is the difference between a terrarium and a prop box, then? Both contain plants within a clear covering that lets light in and holds moisture in the air, but the distinction is both aesthetic and practical. The terrarium takes centre stage in your plant room, displayed proudly on a table, and the plants inside tend to be established rather than rooting. The prop box is usually kept behind the scenes; the boiler room of the plant operation that is not a display unit but a practical feature containing young plants you want to raise. You can make an aesthetically pleasing prop box if you wish - scroll to the bottom of this page for some examples from planstagram.

How to start your first prop box

You can get started without buying a single thing or leaving the comfort of your home. First find your prop box. You can use any clear plastic container with a removeable lid, from the box your food arrives in from the local Chinese takeaway to a plastic food tray from the supermarket with a bit of cling film (plastic wrap if you're not British) stretched across the top (that's what you can see in the picture above). A clear plastic zipped bag also works really well, and the ambassador absolutely loves it when you use a Ferrero Rocher box, by the way.

Next, choose your substrate. You can utilise all kinds of things here, and the cheapest and most convenient is some kitchen roll or paper serviettes. Lay the paper on the bottom of your box and add water until it is damp but not sopping wet, then place your cuttings on top. The only downside is that the roots can get properly tangled in the damp paper, which makes potting on a bit fiddly. If you have horticultural grit, fine gravel, pon, expanded clay pebbles (aka leca), perlite or vermiculite, you can also use these, just make sure you rinse them thoroughly first (and wear a mask whenever dealing with perlite and vermiculite as the dust is bad for your lungs). The final option is sphagnum moss. I have mixed feelings about this substrate because sphagnum is often harvested from the under-threat ecosystems of peat bogs. At the very least make sure the sphagnum you use is collected under licence, and reuse it for as long as possible: you won't need much at all.

Here's the sciencey bit - how vegetative propagation works

Next, take your cuttings. But what do you cut, and where? If you want to make more houseplants, most people choose taking cuttings (vegetative reproduction) rather than sowing seed (sexual reproduction), because it's usually quicker, and you end up with exactly the number of plants you need that are exact replicas of their parent.

Growing plants from cuttings is effectively cloning the plant - the DNA of a cutting will be exactly the same as that of the parent plant. Not all cuttings will grow the same way, and that's not down to the whim of the gardener, but the way different plants choose to reproduce themselves. They key is the location of a particular type of plant tissue called meristematic tissue. These contain stem cells that can turn into roots, or stems (in botanist-speak, they are totipotent - that's a word to use over your next coffee with a fellow planty person).

Meristematic material can be spread across the whole plant, or focused in particular areas, such as nodes along the stems, and their location often tells you something about the plant's way of living. For instance, the jade plant (Crassula ovata) has a brilliant survival strategy: rather than possessing herbivore-repelling spines or hairs, it has the ability to reproduce from the smallest fragment of plant material - its meristematic material is spread throughout the plant. So when the jade is munched by herbivores such as tortoises or elephants, any dropped snacks can root into new plants.

The wax plant (Hoya carnosa), on the other hand, produces roots from its stem: this species anchors onto trees in parts of China, Japan and Taiwan, so it is able to root wherever a stem touches fertile ground in the form of a pocket of canopy soil. You don't necessarily need to know where a plant's meristematic material lies to propagate cuttings: you can experiment with different options and see what works and roots, but it certainly saves time to know if you need to take a leaf, a stem or even a different plant part (weird fact: venus fly traps (Dionaea muscipula) will propagate from a flower stem). You can read about jade plants, the wax plant and the venus fly trap in-depth in my book Legends of the Leaf.

What species can I put in a prop box, specifically?

The options are very wide. Most houseplant species are subtropical or tropical in origin, and therefore will love the environment of a prop box. This even applies to many succulent plants such as holiday cacti and other epiphytic South Americans such as Rhipsalis (mistletoe cacti): you may wish to add some ventilation holes to improve air circulation. Desert cacti generally won't enjoy are prop box, but there are exceptions so you can always give it a try. If you don't have any houseplants to take cuttings from, some houseplant sellers offer cuttings boxes which are good value, or ask for cuttings from houseplant-growing friends and family.

Caring for a prop box

Once you've taken your cuttings, place them inside your prop box, laying them gently on the substrate before closing the lid tight. Place the boxes somewhere light, but not in full sun where they'll fry. Putting them under LED growlights will help to speed up growth, especially in winter.

Make sure you check in with your boxes every few days. While you're at it, spray down the cuttings and substrate if they are starting to dry out, then check your plants. You may find some cuttings start to rot: this happens from time to time, so just carefully remove anything that's unhappy and resign to the compost, and check more regularly. The smaller the box, the more often it's advisable to open the lid and let some fresh air circulate. Tiny prop boxes like the ones pictured above may need to be attended to every few days, whereas really large tubs can go weeks or even months without being opened.

Once your cuttings have grown decent roots - what next? If your cuttings have roots that are a third to a half the length of their total length, it's time to move them into pots in your substrate of choice. (Read my piece on houseplant repotting for more help choosing what to grow in). These baby plants' root systems are still fragile, so it's wise to keep supporting the plants with extra protection and humidity. You can do that by placing each individual pot lock stock and barrel inside a clear plastic bag, or simply upgrade your prop box to a large clear plastic tub big enough to pop your pots in. After a few weeks and as they start to grow, gradually increase the time these new plants spend with the lid off the box, until they are ready to join the rest of your collection, or be passed on to a friend.

But I am an outdoor gardener!

I hear you - but prop boxes can work for you too. In a few weeks you may well be facing the dilemma of having loads of young tender veg plants - tomatoes and chillies, for instance - that need to be gradually exposed to the outside conditions. Placing pots in large prop boxes will allow you to move them in and out with ease: you can take the lid off to give them some fresh air and gradually increase their exposure as the weather warms.

Props to you

So now it's over to you - I'd love to know what you've tried raising in a prop box, and I'm happy to answer any questions about the prop box process, so fire away in the comments below!