Companion Plant Seeds for Your Cannabis Grow

Here's the myth worth killing early: companion plants are not a pesticide in plant form. Nobody sows a row of calendula and gets a bug-free plot. What a companion planting does is change the odds. Flowers bring in the insects that eat the ones chewing your leaves, aromatic herbs muddle the scent trail pests follow, ground-huggers stop your soil baking dry, and tall stuff simply gets in the way of a nosy line of sight. Think of it as building a garden your cannabis happens to live in, rather than bolting a gadget onto a pot.

Four Jobs, and the Species That Do Them

The Buddy Mix Packs are named after the job, which makes this shelf easy to shop. SCARE leans on smell and taste to push insects off. DEFENDER is the border guard, sown round the edge of a bed so trouble meets it first. STEALTH is about height and bulk, the plants that turn a suspicious cluster of pots into a herb patch. NUTRIENT covers the soil crew, the ground cover and the legumes that put something back while your main plants take.

Underneath the mixes sit the single-species options. Buddy Packs come one plant per pack: Sunflower, Marigold (Calendula officinalis), Cerastium, Alfalfa, White Clover, Red Clover, Chervil, Peppermint, Lavender, Coriander, Dill, Lemon Balm, Sweet Basil, Borage, Chamomile and Yarrow. The loose seed packets add the kitchen end of things, with Sage, German Winter Thyme, Oregano, Parsley 'Curly Dark Green', Cumin, Lovage, White Mustard, Dandelion, Catmint and Rue. A mix pack is the better buy if you're starting from nothing and want cover fast. A single Buddy Pack is the better buy if you already know the gap you're filling, say a metre of empty edge that needs Marigold and nothing else. Everything sits in the wider plant seeds range if you want herbs for their own sake too.

SCARE and DEFENDER: Pushing Bugs Somewhere Else

Marigold is the classic front line. Calendula has been used as a showy border plant in prized gardens for exactly this reason, and it's known to deter beetles, leaf hoppers, Mexican bean beetle and bad nematodes. The Latin label on the French marigold side of the family is Tagetes and root-knot nematode suppression is the effect growers are really after, because it produces a chemical in its roots strong enough that the effect lingers for years after the plants have died back. Once the flowers have gone over, the foliage is good compost material.

Sunflower plays a different trick: it's the decoy. Aphids find that big soft stalk more interesting than your cannabis, and the plant is tough enough to shrug off a lot of insect attack thanks to thick stalks and leathery leaves. Better a sunflower gets chewed than your best plant. Catmint (Nepeta mussinii) earns its place twice over, pulling pollinators in while putting mosquitos and cockroaches off, and it'll take a moderate dry spell once it's established.

The aromatic crew fills in around them. Peppermint, Coriander, Dill, Chervil and Yarrow are traditionally sown as border and interplanting herbs, and the smell is half the point. Crush a peppermint leaf between your fingers and it leaves a cold, sharp smell on your skin for a good ten minutes, which tells you how much volatile oil is in there. Rue (Ruta graveolens) belongs in this camp too, but read the label before you buy: rue can irritate skin on contact, sunlight makes that reaction worse, and it shouldn't be eaten by anyone pregnant or dealing with liver problems. Gloves on whenever you weed near it. If you want a fragrant border with none of that hassle, Lavender does a similar job and you can actually pick it.

STEALTH: Making a Grow Look Like a Garden

Concealment is mostly geometry. A cannabis plant is recognisable because of its outline and because it's usually the only thing there. Break both and you've done most of the work. Sunflowers give you the height, standing head and shoulders above everything else in a single season, with that big yellow head nodding east once it matures. Lavender and Borage bulk out the middle layer. Cerastium (Cerastium biebersteinii) mats across the soil in silvery grey leaves with a shower of white flowers in late spring, so the ground reads as planted rather than dug.

Watch out for the obvious trade-off: tall companions cast shade and drink hard. Sunflowers are drought tolerant and root deep, which means they'll happily take water your cannabis wanted, and a row of them on the sunny side will shade your canopy at midday. Put the height where the sun isn't coming from. Same warning on Cerastium, it's a rapid perennial that can turn invasive, so don't be shy about hacking into it when it gets greedy for room.

Short on ground? The Geotextile Fabric Wall Planter (10L) hangs on a wall or fence and takes fragrant herbs, so a balcony grow can sit behind a screen of Sweet Basil and Peppermint. It's made from recycled PET, and excess water just runs through instead of drowning roots. For younger plants the smaller Geotextile Transplanter Pot makes more sense than a 10L wall unit. The Pot Marker packs in black and gold keep track of what went where, which matters more than you'd think once sixteen seedlings all look like green fuzz. Both live with the rest of the kit in the growshop.

NUTRIENT: Clover, Alfalfa and Soil That Stays Alive

This is the section growers skip and then regret. Bare soil bakes, crusts and loses water. A living mulch shades it. Cerastium is the specialist here, a dense mat that cuts moisture loss to evaporation and throws out a lot of foliage in a short life, all of which goes back into your compost heap.

White Clover, Red Clover and Alfalfa are legumes, which is why growers have sown them under and around crops for centuries. Nitrogen fixation is the shorthand for what's going on below the surface: they work with soil bacteria at the root, and the top growth can be cut and dropped as mulch whenever it gets long. Chamomile, Borage and Lemon Balm bring flowers that keep insects busy in the same beds. Dandelion (Taraxacum officinale) sends down a serious taproot that opens up compacted ground, and its relative Chicory is the root you dry and grind as a coffee stand-in.

The honest catch: in containers, these plants are competition. A pot has a fixed amount of root space and water, and alfalfa roots go deep looking for both. Save the soil crew for beds, borders and the ground your pots stand on. If you're strictly in fabric pots indoors, a clover undersowing does less for you than a decent mulch and a feeding schedule.

Sowing Windows, Bad Neighbours and What Ends Up in the Teapot

Most of this shelf keys off one date: your last frost. In much of the UK that's a May job, later if you're north or high up. Sunflowers go in once frosts have passed. Catmint can be sown straight outside in late spring. Sage, Lovage and Parsley are happier started in an indoor propagator or on a warm windowsill and moved out after the frosts, once they've got their first true leaves. White Mustard is the early one, sown in March and ready over the summer, which makes it handy as a quick soil cover before the main season. Cumin is the fussy one: start it about four weeks before the last frost, only move it out once temperatures sit above 15°C, and expect roughly 120 days to harvest, so it wants your hottest, driest corner.

What to keep away from your cannabis: anything that wants the opposite conditions. Sage, German Winter Thyme and Oregano all want full sun and sharply drained soil, while Parsley likes fertile ground and regular water, so those two groups don't share a container well. Peppermint and Lemon Balm run underground and will colonise a bed, so keep them in their own pot. Cerastium takes over at surface level. Rue is a poor neighbour for anything you'll be handling constantly, given the skin reaction. And because French marigold roots leave an insecticidal residue that hangs around for years, plant it where you're happy for that to stay put rather than in the pot you'll be reusing next season.

The other reason to grow these: the kitchen. Sage leaves crushed between your fingers give off that dusty, savoury smell and make a good tea. German Winter Thyme goes wherever oregano would. Lovage leaves and roots are fine cooked or raw in a salad. White mustard seed does pickles and sauces, young leaves do salads. Catmint brews up too, assuming the cat lets you keep any.

Our pick if you're outdoors this year: DEFENDER round the perimeter, White Clover under and between the pots, and a couple of Sunflower Buddy Packs on the shaded side for height. On a balcony, drop the sunflowers entirely and fill the Wall Planter with Sweet Basil, Peppermint and Lavender instead.