Shiso

Shiso is a plant that rewards you in the first season and then tests your commitment to garden boundaries in every season after. One plant becomes thirty the next year if you let it go to seed — and you will let it go to seed, because by the time you notice the flower spikes, they've already set. The seedlings come up thick in spring, in the bed and in the paths and sometimes in the lawn, and the gardener who planted shiso two years ago spends the third year pulling volunteers.

There are two main types, and the distinction matters if you're cooking. Green shiso — ao-shiso — has a bright, anise-mint-basil flavor that works raw in salads, with sashimi, or fried as tempura. Red shiso — aka-shiso — is darker, more astringent, and used mostly for pickling and coloring umeboshi plums. The red is also the one that tends to show up as an ornamental in garden centers, labeled as something like 'Magilla' — which is fine for looking at, but not the one you want if you're making onigiri.

Germination can be slow or spotty unless you prepare the seeds. A cold stratification — three or four weeks in damp sand in the refrigerator — tends to improve the rate noticeably. Some gardeners skip that and instead soak the seeds overnight or lightly scarify them by rubbing between two sheets of fine sandpaper. Once the seedlings are up, they grow fast and tolerate partial shade better than most herbs, which makes them useful in spots where basil would sulk.

The plant tends to branch freely without much pinching, and you can harvest leaves continuously once the plant is eight or ten inches tall. Pinching out the flower spikes as they form extends the harvest window and keeps the leaves from turning bitter, but more importantly, it prevents the reseeding problem. If you want shiso next year, leave one plant to flower. If you want shiso everywhere next year, leave them all.

Shiso has few serious pests, though Japanese beetles will chew the leaves if they're around. The main thing that tends to go wrong is bolt-and-spread — the plant flowers earlier than expected in hot weather or long days, sets seed before you notice, and the next spring you have a hundred seedlings where you wanted ten. Deadheading flower spikes the moment they appear is the only real control.