Every plant, by section

The types of plants, and which types this index covers

Types of plants can be sorted in three ways that actually change what you do: how long the plant lives, what kind of stem it builds, and whether it keeps its leaves through winter. Everything else, including the seven sections this database is organized into, sits on top of those three. Read this once and the label on a plant tag stops being jargon.

Plant types by life cycle: annual vs perennial, and biennials

The first question about any plant is how many seasons it gets. The annual vs perennial distinction decides what you pay, when you plant, and whether the gap it leaves in October is permanent. Perennial plants come back from the same roots; annuals have to be bought again.

Two complications are worth knowing before you buy. Plenty of plants sold as annuals in cold states are tender perennials that simply cannot survive the winter there: geranium, lantana and tomato all live for years in a frost-free climate. And a perennial is only perennial in a zone where it survives, which is why every entry here states a hardiness range instead of repeating the word.

Plant types by form: herbaceous plants, shrubs, trees and climbers

The second question is what the plant builds. Woody plants keep a permanent structure and grow bigger on it every year; herbaceous plants build soft growth that dies back and starts again.

The line between a shrub and a small tree is a matter of training as much as botany. The same species is sold as a multi-stemmed shrub or as a standard on a single trunk, which is why hydrangea appears in this database twice, once as a shrub and once as a tree form.

Evergreen vs deciduous types

The third question is what the plant looks like in February. Evergreen plants hold their leaves or needles all year and carry the structure of a garden through winter. Deciduous plants drop their leaves in autumn, which sounds like a loss and is often the point: they let winter light through, then feed the soil with the leaves they drop.

• Most conifers are evergreen, but not all: larch and bald cypress are conifers that drop every needle each autumn.
• Broadleaf evergreens include azalea, holly and many rhododendrons, and they still lose water through their leaves in winter, which is why they need water in a dry autumn.
• Semi-evergreen plants keep their leaves in a mild winter and lose them in a hard one, so the same shrub behaves differently in zone 7 and in zone 5.

Deciduous plants are not failing when they drop their leaves. Dropping is a strategy: a broad thin leaf loses water fast, and in a season when the ground is frozen or bone dry the roots cannot replace it, so the plant seals the leaf off and lets it fall. Evergreen plants take the other route, with small, thick or waxy leaves and needles built to hold water through the same season, which is why they can keep them.

The practical rule for a garden is to keep roughly a quarter to a third of the woody planting evergreen. Less than that and the garden disappears from November to April. Much more and it never changes, which removes the thing deciduous plants are actually for.

Hardy, half-hardy and tender

This is the classification that decides whether a plant lives, and the one gardeners most often meet only after losing a plant. It is not the same question as the life cycle: a plant can be a true perennial in its native climate and still be sold and grown as an annual where winters are colder.

The label on a pot describes an average zone rather than yours, which is why every entry in this index carries a hardiness range instead of the word hardy. A salvia that is a dependable perennial in zone 8 is an expensive annual in zone 5, and neither the grower nor the label is wrong. They are describing a different garden.

Native, introduced and invasive

A fourth way of sorting the same plants has become part of how gardeners choose, and it is worth stating plainly because the terms get used loosely.

• Native plants evolved in your region and support the insects and birds that evolved alongside them. They are not automatically easier to grow, but they are usually well matched to local rainfall and soil.
• Introduced plants come from elsewhere and behave themselves. The great majority of garden plants sit in this group, and being non-native is not a mark against a plant.
• Invasive plants are introduced plants that spread on their own, out-compete what is already there, and cannot be recalled once they are loose. Invasiveness is regional: a plant that is well behaved in one state is listed as invasive in another.

Check a plant against your own state list rather than a national one before planting anything that spreads by runner, sucker or berry. That check costs a minute, and it is the only part of plant choice that affects land you do not own.

Flowering plants, ferns and the rest

Not every plant flowers, and the ones that do not are grouped by how they reproduce rather than by how they look.

• Flowering plants, the angiosperms, are the vast majority of garden plants, and they include orchids, which form one of the two largest flowering plant families.
• Conifers reproduce with cones rather than flowers, and include most of the evergreen trees and shrubs used as screens and hedges.
• Ferns reproduce by spores, never flower, and are grown for foliage in shade and as houseplants.
• Succulents and cacti are not a botanical group at all. Succulent describes a plant that stores water in its leaves, stems or roots, and that adaptation turns up across many unrelated plant families.

Bulbs, corms and tubers

A bulb is not a separate kind of plant so much as a storage organ, and the plants that build one are perennials that spend most of the year underground. Tulips, daffodils and hyacinths grow, flower, refill the bulb and then vanish until the following spring, which is why they share a bed happily with later perennials that cover the gap they leave.

• Spring bulbs are bought and planted in autumn, months before anything shows above ground.
• Summer bulbs, corms and tubers such as dahlia and gladiolus are planted after frost and lifted again in cold zones.
• Bulbs are commonly sold as dry stock rather than as growing plants, which is why the planting depth on the packet matters more than for anything else you buy.

Indoor plants and outdoor plants

The same plant types appear indoors, but one field disappears and two others take over. Houseplants have no hardiness zone, because the coldest night they will ever see is whatever the thermostat allows. What decides them instead is light, which indoors is a fraction of what the same plants would get outside, and watering, because nothing in a living room dries a container out except the plant and the air.

Most popular indoor plants are tropical perennials grown for foliage: they are permanent, they grow slowly, and they are read as easy or difficult almost entirely on how forgiving they are about water.

How botanists sort the same plants

The sorting above is horticultural: it answers what you do with the plant. Botanists sort the same species by structure and reproduction, and those categories explain why some plants behave so differently.

Two of those groups explain habits that otherwise look arbitrary. Spore plants such as ferns produce no flowers and no seeds at all, so nothing you feed them will make them bloom. Aquatic plants tolerate soil that stays saturated, a condition that kills almost every other type of plant on this page by drowning the roots.

How the seven sections map onto plant types

This index groups plants by how people look for them, not by botanical family, and the seven sections cut across the types above rather than replacing them.