Botanical illustration has four principal media, and every serious program teaches them roughly in the order below. Most illustrators eventually specialize in one or two, but the choice for any particular plate is a practical one — what the plant needs, what the plate is for, how much time there is, and how it will be reproduced. Here is how the four compare.

Graphite

What it does best: form. Graphite renders the three-dimensional structure of a plant — the turn of a petal, the depth of a flower throat, the twist of a leaf — with more subtlety than any other medium, because tone can be graded almost infinitely and corrected almost indefinitely. It is also the medium of the construction drawing under every other medium, so it is never wasted learning.

Limits: no color, obviously, which means species distinguished mainly by color (many penstemons, the blue of a columbine) need notes or a second medium. Graphite reproduces slightly gray in print unless scanned carefully, and it smudges in handling.

Cost and speed: the cheapest medium by far, and fast to start; a finished plate takes as long as you give it. Learning curve: gentle to begin, long to master — continuous tone and edge control take years. See the graphite techniques guide.

Pen and Ink

What it does best: line, and reproduction. Ink drawings are pure black on white, which means they print perfectly at any size, photocopy cleanly, and remain the standard for taxonomic floras, scientific papers, and field guides. Ink forces decisions: every mark is either there or not, so an ink drawing is a set of clear statements about margin, venation, hair, and structure. Stipple (dots) builds tone for smooth surfaces; hatching builds it for directional ones; line weight alone can carry form.

Limits: unforgiving. Mistakes are scraped, painted over with white, or redrawn. Subtle tonal gradation is laborious in stipple and impossible in pure line. Ink does not describe color.

Cost and speed: inexpensive (technical pens or dip pens, waterproof ink, smooth paper), moderate speed — faster than watercolor for a habit, slower for tone. Learning curve: the hand control comes with practice; the design sense — knowing what to leave out — comes with knowledge of the plant.

Colored Pencil

What it does best: control. Colored pencil is applied dry, in layers, with no drying time, no water, and no unpredictable behavior — every mark stays where it is put. That makes it ideal for fine detail (the striations on a petal, the bloom on a plum), for very gradual color transitions, and for artists who want to work slowly and precisely. Modern wax- and oil-based pencils are lightfast and produce a surface with real depth. Burnishing with a colorless blender gives a smooth, saturated finish; solvent blending gives a painterly one.

Limits: slow — a full-color plate in pencil takes many hours of layering, often longer than the same plate in watercolor. Large areas of flat color are tedious. Very dark values are hard to reach without wax bloom (a hazy film on heavy applications). Pencil can also look "penciled" — a slight granularity — unless the paper and pressure are well managed.

Cost and speed: moderate to expensive (a good set is a significant purchase, though it lasts years); slow. Learning curve: the easiest color medium to get an acceptable result from, and a long road to a luminous one.

Watercolor

What it does best: luminosity. Transparent watercolor on white paper produces color with light behind it, and no other medium renders the translucency of a petal or the glow of a berry so convincingly. It is also the historical medium of botanical art from the great eighteenth- and nineteenth-century florilegia, and the medium most exhibition and society work is judged in. Dry-brush watercolor — the botanical technique of building tone with a nearly dry brush in many fine layers — gives control approaching colored pencil while keeping the transparency.

Limits: water is unpredictable, corrections are limited, and white must be planned (the paper) rather than added. Watercolor demands a confident construction drawing and a clear plan for the order of washes. It is the medium in which beginners most often produce a muddy plate.

Cost and speed: moderate (a limited palette of good paints, a few brushes, and cotton hot-press paper); faster than colored pencil for coverage, slower than ink for line. Learning curve: the steepest of the four, and the medium in which the most is possible once it is climbed.

Matching Medium to Subject

• Structure-dominant plants — grasses, sedges, conifers, dried seed heads, anything where form and pattern matter more than hue: graphite or ink.
• Color-diagnostic flowers — where hue identifies the species or is the point: watercolor or colored pencil.
• Waxy, glossy, or bloom-covered surfaces — plums, cactus pads like the prickly pear, many succulents: colored pencil's control over highlights and bloom is hard to beat, though watercolor can do it with careful reserving.
• Translucent petals — poppies, evening primrose, crocus: watercolor.
• Fine hairs and texture over a colored ground: colored pencil over a watercolor underpainting is a common and effective combination.
• Anything for reproduction in a scientific text: ink, or graphite if the printer can handle halftones well.

Mixed Media

The boundaries are porous. A watercolor underpainting with colored-pencil detail on top is one of the commonest working methods among contemporary botanical artists; ink line with watercolor wash is the classic field-guide look; graphite with a single accent of color on the flower is a favorite for exhibition. The general rule is that the wetter medium goes down first and the drier one on top, and that the paper must suit the wet medium. Combining media is a way to get the strengths of each — watercolor's luminosity in the washes, pencil's control in the last details — and it is worth experimenting with once each medium is comfortable on its own.

Vellum

Calfskin vellum — a prepared animal skin, not the paper called "vellum" — is the traditional support for the finest botanical painting, and watercolor on vellum has a depth and glow that paper cannot match. It is expensive, it must be prepared and handled carefully (it responds to humidity), and it takes only dry-brush technique; wet washes buckle it and lift the surface. Vellum is for a finished exhibition piece by an artist who already commands watercolor on paper, not for learning on.

How to Decide

Ask four questions. What is the plate for — print, wall, portfolio, study? What is diagnostic about this plant — form, color, texture, line? How much time is there? And which medium are you competent in today, rather than the one you wish you were? The honest answer to the last question overrides the others more often than beginners like. A well-rendered graphite plate of a blue flower is a better plate than a muddy watercolor of the same flower — and it can always be the study for the watercolor next year. Build the graphite foundation, add ink for print, and then decide whether your temperament is the patience of colored pencil or the risk of watercolor. Most illustrators find that one of the two feels like home, and the plates get better the moment they stop fighting it.