Green and Red Shiso: How the Types Differ and Which to Grow

Green and red taste genuinely different

The most common mistake is to assume the two colors are interchangeable and to pick whichever looks better on the seed packet. They are not. Green shiso is the aromatic one: bright, sharply scented, with notes people describe variously as mint, basil and anise, and it is the type to grow if you want to eat the leaves fresh in quantity.

Red shiso is milder in scent and noticeably more astringent, with a slight bitterness in the leaf. Its distinguishing property is pigment. Steep red leaves in anything acidic and they release a clear crimson that dyes vinegar, brine or syrup a deep, even color. Green shiso does none of this. If you are growing for color, red is the only option; if you are growing for scent, green wins by a wide margin.

Leaf shape: flat and ruffled forms

Independent of color, shiso comes in flat-leaved and crinkled or ruffled-leaved forms, and the difference is practical rather than decorative. Flat leaves are easy to wash, easy to stack and wrap, and easy to use whole. Ruffled leaves have a much larger surface area for their size, which looks striking but traps water in the folds, holds grit, and gives aphids and mites somewhere to sit out a water spray.

In a wet climate a ruffled form is measurably more prone to leaf spot, because the crinkles hold moisture long after a flat leaf has dried. If you have had fungal trouble, choosing a flat-leaved form is a cheap improvement.

Bicoloured forms, green on top and red beneath, sit between the two in both scent and pigment. They are pleasant plants but they are not a substitute if you specifically need one property or the other.

Ornamental forms are bred for looks, not for eating

The same species is also sold as a bedding plant, grown for deep purple-black foliage and used as a filler in borders and containers. These forms are not toxic, but they have been selected purely for leaf color and habit, and the scent has generally been bred out or was never there. A leaf can look magnificent and taste of almost nothing.

If you buy a plant from an ornamental bedding display rather than a herb bench, crush a leaf between your fingers before you commit to it. A culinary shiso announces itself immediately; an ornamental one smells faintly green and nothing more.

1. Crush a leaf and smell it This is the only test that matters and it takes two seconds. Strong distinctive scent means a culinary type, regardless of what the label says.
2. Check where it is being sold Plants on a bedding or foliage display are usually ornamental selections. Plants on a herb bench are usually culinary. It is not a guarantee, but it is a good prior.
3. Do not save seed from ornamentals Seed from an ornamental form will produce more ornamentals, and if it crosses with your culinary plants you will dilute those too.
4. Keep them physically apart If you want both, grow the ornamental in a container well away from any plants you intend to collect seed from.

Growing green and red together means they will cross

Shiso is insect-pollinated and crosses freely between colors and between culinary and ornamental forms. This does not affect the leaves you are picking this year at all, so grow them side by side without worrying. It affects the seed. Seed saved from a garden with both colors produces a muddled mixture the following year: dull purple-green leaves with neither the scent of the green type nor the pigment of the red.

This matters far more with shiso than with most herbs, because the plant self-seeds so freely that you end up growing next year's crop from that crossed seed whether you intended to or not. Within three or four generations of unmanaged self-seeding, a garden's shiso reverts to a nondescript intermediate.

The simplest workable approach for most gardens is to buy fresh seed of the type you want each year and cut every flower spike before it sets. It removes both the crossing problem and the self-seeding problem in one job.

Choosing for the space you actually have

Type also interacts with where you are growing. A vigorous green form given a bed and pinched three times becomes a bush two feet across and produces far more than most households use. In a container the same plant is limited by root volume and needs daily water in summer, so a smaller, more restrained form is easier to keep alive.

Red forms tend to be slightly shorter and slower, which makes them the easier choice for pots and window boxes, and their color earns them a place in an ornamental container in a way a green herb does not.

1. Open ground, want maximum leaves Green, flat-leaved, one or two plants at sixteen to twenty inches (40 to 50 cm) spacing, pinched three times. This will out-produce four crowded plants.
2. Container on a sunny balcony One plant per ten inch pot. A red or a compact form copes better with the restricted root run and the inevitable missed watering.
3. Growing specifically for preserving color Red, and enough of it: coloring a batch of vinegar or brine takes a surprising volume of leaf. Plan on three or four plants, not one.
4. Cut-and-come-again for small leaves Either color, sown thickly at six inch (15 cm) spacing and cut young. You get tender leaves quickly and clear the ground before flowering becomes an issue.

Note down which type you grew, where it stood, and what you thought of the scent at the end of the season. Shiso varies more from garden to garden than the packets suggest, and your own two-line verdict is worth more than any description.