Growing in pots: what survives, what needs the ground

A courtyard, a balcony or a paved side return gives you no open ground, so everything lives in a container. Pots disappoint in a familiar pattern: right for a season, holding through a second, going backwards in the third. A pot is a small, hot, leaky root zone with a hard wall around it, and nearly everything else follows from that.

Pot size sets the ceiling

Undersized pots fail two ways at once. Roots run out of room and circle the wall, and the mix is too small a volume to hold water for a hot day. Such a plant is thirsty every day no matter how carefully you water, because you are refilling a cup rather than a tank.

As a working guide, succulents and small ferns are content in 200mm to 300mm containers, a shrub you want to keep for years wants 400mm across and roughly as deep, and a small tree or a clumping palm needs 500mm or a half wine barrel. Depth matters as much as width, so avoid shallow bowls for anything woody. Do not jump from a 200mm nursery pot into a 600mm feature pot either: mix that no root reaches stays wet and sours. Step up one or two sizes.

Potting mix, never garden soil

Garden soil works in the garden because worms, roots and soil life keep it open. None of that happens in a container. Within a few waterings it slumps into a dense block, the air spaces close, and roots drown in a pot that still looks well drained on top.

Use a bagged mix carrying the Australian Standard mark, and take the higher grade where one is offered. Match it to the plant: gritty, with coarse sand or perlite, for succulents and agaves; a standard mix for palms and ferns; a camellia and azalea mix, which sits on the acid side, for camellias and Japanese maples. Skip the gravel in the base, since a coarse layer under a fine mix raises the level at which water sits rather than lowering it.

Drainage, and why saucers kill plants

A full saucer turns the base of the pot into a reservoir. The bottom band of mix stays saturated, the roots in it die, the plant reads as thirsty above ground, and the usual response is more water. Indoors, empty the saucer half an hour after watering. Outdoors, use pot feet and never stand a container flat on paving, where the holes seal against the surface. Check the holes are open, since roots and shipping discs block them.

Watering through an Australian summer

Through January a 300mm pot in the open can want water daily, and a 500mm one every second or third day. Wind dries containers faster than heat does, so an exposed balcony is harder work than a sheltered hot courtyard. A dark pot in full sun on paving also cooks the roots against the wall, so choose a pale or thick-walled one. Push a finger 40mm into the mix rather than trusting a timer or the surface.

Water until it runs freely from the base, then stop, because a splash wets the top 20mm and nothing else. Old mix turns hydrophobic, and water then races down the gap between root ball and pot wall, leaving the centre dry. If the pot feels light straight after watering, soak it in a tub for twenty minutes and use a wetting agent each spring.

Feeding, because containers leach

Every time water runs out the bottom it takes dissolved nutrients with it. A plant in the ground draws on a reserve that is constantly resupplied; a potted plant has only what you put in, and fresh mix runs out within months. Apply a controlled-release fertiliser as growth starts in spring, top it up in midsummer, and liquid feed every two to three weeks through the season.

Use the container rate, not the garden rate, since in a confined volume an overdose burns roots. Then read the leaves: pale yellow-green overall is nitrogen, yellowing between the veins of older leaves is magnesium, yellow new leaves with green veins is iron.

Repot or root prune before the plant stalls

Most people repot after the decline, which costs a season. Work to a cycle instead, every two to three years for woody plants. The warning signs, roots out the drainage holes, water pooling on the surface and a pot that dries in half a day, mean you are already late.

Repot in late winter for deciduous plants and early spring for evergreens, before the flush. Slide the plant out, cut circling roots, shave 20mm to 30mm off the sides and base of the root ball, and set it back at the same depth in fresh mix. Hold off feeding until new growth appears. To keep a plant in the same container, root prune and return it with fresh mix. That is how a box ball or a maple lives in one pot for decades. Palms are the exception, since most resent root disturbance, so move them up a size without cutting.

Plants that genuinely last in containers

Shaded courtyards and covered balconies

Clumping palms are among the few plants content to sit pot-bound for years. The Kentia Palm and Lady Palm are slow, fine-rooted and tolerant of low light, and Bamboo Palm suits a narrow shaded return. None are toxic, which matters in a family courtyard. More sit in the palm range. The Bird's Nest Fern grows on tree trunks in the wild, so a modest root volume suits it, as it does most of the fern range, tree ferns aside.

Hot, exposed positions

Succulents are built for shallow, sharply drained root zones, which is exactly what a pot is. Foxtail Agave carries no terminal spine, so it is safer around children than most agaves, although the sap can irritate skin and eyes. Jade plants and most other crassulas are toxic to cats and dogs, so keep those pots out of reach. Browse the succulent range and the low maintenance range for hot paved sites.

Structure and flowers

Clipped Japanese Box topiary balls are a genuine long-term container subject, with dense fibrous roots that take clipping and confinement. Box leaves are toxic if eaten, so think twice at nose height where a toddler or a chewing dog is about. And box scorches in a hot dry courtyard, so give it half a day of sun. The buxus range and topiary and standards cover the shapes.

Sasanqua camellias have shallow fibrous roots that suit containers, and they flower through autumn and winter. Setsugekka takes clipping and a half-sun position. Camellias are not toxic, but they resent drying out while setting buds, so summer neglect costs the following flowering. See the camellia range.

A Japanese maple is the classic courtyard container plant, and weeping dissectum forms such as Inaba Shidare stay compact enough to suit one. It wants morning sun with afternoon shade, shelter from hot dry wind, which scorches leaves more than sun alone does, and root pruning every second or third winter. Our guide to Japanese maples in Australian gardens goes further.

What is only ever temporary in a pot

Anything that sets out to build a trunk and become a tree is passing through. Single-trunk palms such as Alexandra, Bangalow, Foxtail and Canary Island date, along with the tree aloes, look right for two or three years and then need open ground. Tree ferns will sit in a pot but want constant moisture, and on hot paving they brown off.

What not to do

Do not fill a pot with garden soil, add gravel to the base, or leave water standing in a saucer. Do not stand pots flat on paving, or shift a small plant into a very large container. Do not stand a standard on a clear trunk in a light pot, because wind tips it and the rocking damages roots. Do not feed a plant that is dry or stressed; water it first. Do not answer a wilting plant with more water before checking the mix, because waterlogged roots wilt exactly like dry ones. And do not put succulents or agaves in a self-watering pot, which is built to do the one thing they cannot tolerate.

Some plants are better skipped. Hill's weeping fig standards hold in a container but need root pruning on a short cycle, and should never go into a small courtyard bed near paving or drains. Citrus is worth a pot but runs on its own rules, covered in growing citrus in pots and gardens.

Getting it right from the start

Buy the pot before you buy the plant. Get the pot, the mix and the watering right and the plant list becomes the easy part. Every order ships farm-direct with flat $99 delivery in QLD, NSW, VIC, SA, ACT and WA, a $399 minimum order, and the 30-Day Healthy Plant Guarantee.