Start With the Leaves, Not the Flowers

It is easy to be seduced by a plant in full bloom. A flowering kalanchoe or a supermarket orchid will stop you in your tracks, and rightly so. But flowers are the shortest-lived part of any houseplant, and a stunning display can mask a plant that is quietly struggling. Before you fall for the petals, spend a minute or two with the foliage. It will tell you almost everything you need to know about how the plant has been treated since it left the nursery.

Healthy foliage is consistent. Whatever the natural colour of the leaves, it should be even across the whole plant, with no pale patches, no mottling and no crispy brown edges. New growth is usually a shade lighter or slightly softer than mature leaves, which is perfectly normal. What you are looking for is a plant that looks like it has been growing steadily rather than one that has been pushed fast and then left to sit in a warm, dim shop for a fortnight.

What Healthy Leaves Look Like

Pick up the pot and turn the plant slowly, inspecting both the top and the underside of the leaves. The undersides are where problems hide, because that is where pests gather and where early signs of trouble show first.

• Firm, glossy leaves with a slight natural sheen. Dull, dusty leaves are usually just neglected, but leaves that look greyish or washed out may be struggling.
• An even colour across the leaf, with no yellow halos or brown tips. Yellowing between the veins often points to a nutrient problem, while brown tips usually mean inconsistent watering or low humidity.
• Leaves that hold their shape. A drooping, limp plant may simply be thirsty, but if it does not perk up after a drink it could have root damage.
• Clean surfaces. Sticky residue, fine webbing, tiny white specks or a sooty black film are all red flags for pests such as spider mite, whitefly or scale.

Fiddle leaf figs, monsteras and rubber plants are particularly worth checking carefully, as they sulk for months after a bad start. If a plant has lost most of its lower leaves and the remaining ones are pale, walk away. It will take far longer to bring back than it would to grow a healthy one from scratch.

Check the Stems for Firmness and Colour

Stems are the scaffolding of the plant and they betray problems that leaves sometimes hide. Gently squeeze the main stem between finger and thumb. It should feel firm and slightly springy, like a fresh green bean. If it feels soft, squishy or hollow, that is rot, and it will not recover.

Look at the colour too. On most houseplants, healthy stems are green, or brown and woody on older growth in a natural, even way. Black or dark brown patches, especially near the base where the stem meets the compost, are a sign of overwatering and fungal trouble. You may also spot fine white threads or a fuzzy grey mould in the crevices, which means the plant has been kept too wet and too still.

Finally, look for clear signs of active growth. A new leaf unfurling, a fresh shoot pushing up from the base or a small aerial root forming on a climber all tell you the plant is settled and growing. A plant with no new growth at all in the middle of the season is one to leave behind.

Inspect the Compost and the Roots

The compost is the part most shoppers ignore, and it is often the most revealing. Tilt the pot and look at the surface, then gently tease the plant free if you can do so without damaging it.

• Moist but not sodden. The compost should feel like a wrung-out sponge. If water runs out when you tilt the pot, or if the surface is green with algae, the plant has been sitting wet for too long.
• No sour smell. A whiff of rotten eggs or damp cellar means anaerobic conditions and rotting roots.
• Roots that are pale and firm. Healthy roots are usually white or cream and hold their shape. Brown, mushy roots that come away in your hand are dead.
• Signs of life at the drainage holes. A few roots peeking out is fine, but a dense mat of roots circling the pot means it is pot-bound and will need repotting almost immediately.

While you are there, check the underside of the pot and the rim for tiny insects or their eggs. Fungus gnats, in particular, thrive in constantly wet compost, and a cloud of them rising from the pot is a clear warning.

Look for Pests Before You Pay

Pests spread quickly through a collection, so a few minutes of checking at the till can save months of trouble at home. Turn leaves over carefully and look at the joints where stems meet leaves, which is where many pests like to feed.

• Spider mite shows as fine, dusty webbing and pale speckling on the upper surface.
• Mealybug looks like small white cottony blobs tucked into leaf joints and along the stems.
• Aphids cluster on new growth and leave a sticky honeydew behind.
• Scale appears as small brown or black bumps that do not move when touched.

If you spot any of these, leave the plant where it is. It is not worth the risk to the rest of your collection.

Choose a Plant Suited to Your Home

Finally, remember that the healthiest plant in the shop can still fail in the wrong spot at home. A plant sold as low light will still sulk in a dark hallway, and a sun-lover will scorch on a south-facing windowsill. Check the label, think about the light and warmth your room actually offers, and pick accordingly.

Buy the plant that suits your space, not the one that happens to be on offer. Inspect it properly, take it home the same day and give it a few quiet weeks to settle. Do that and you will be rewarded with foliage that stays glossy and full for years, not just until the flowers fade.