How to read a seed packet

01The packet is a set of conditions

A seed packet is written for a broad climate, not for your garden. The sowing window may span two months, the spacing may assume a market row, and the height may refer to a good year in a warm region. Treat the packet as a set of conditions to interpret, not a promise that the plant will behave the same way on your patch.

The most useful fields are also the least glamorous: botanical name, cultivar, lot code, sowing depth, final spacing and the date the seed was packed. Read those before the picture. A photograph sells the variety; the small print tells you whether it will germinate in your conditions.

02The fields that actually matter

Two more lines deserve attention. “F1 hybrid” means the seed was produced by crossing two parent lines; its offspring will not come true. “Open-pollinated” means the variety can be maintained from seed, provided it is isolated from other varieties that could cross. Neither is better in every garden, but the distinction decides whether saving seed is worthwhile.

03Sow window and succession

“Sow March to May” is not an instruction to sow once in March. It is a window. In a cool spring, the early end may fail; in a warm one, the late end may expose young plants to heat. Use the window with a local signal: soil temperature, last frost, or the emergence of a known weed or tree leaf.

For herbs harvested repeatedly — basil, coriander, dill, chervil — a small sowing every two to three weeks is more useful than one large sowing. Succession spreads the harvest and reduces the risk that everything bolts in the same hot week. For roots and long-season plants, one well-timed sowing is usually enough.

The packet’s “days to maturity” is a scheduling aid, not a guarantee. A dill that matures in 60 days in a warm season may take 85 in a cool one. Add a buffer at the end of the season rather than squeezing a late sowing into a window that is already closing.

04Depth, spacing and light

Sowing depth is a compromise. Too deep and the seedling runs out of energy before it reaches light; too shallow and the seed dries out or is washed away. The packet’s figure is the starting point. As a rough check, cover small seeds barely, and larger seeds to about two or three times their own diameter, unless the packet says otherwise.

Spacing is about the final plant, not the seed. Sow more thickly than the final spacing, then thin in stages: first to remove the weakest seedlings, later to leave the recommended distance. Thinning is not waste; it is the price of choosing the strongest plants. Eat the thinnings where they are edible, and compost the rest.

Some herbs need light to germinate. Chamomile, for example, is often surface-sown. If the packet says “light required”, do not bury the seed to be tidy. Press it onto moist compost and keep the surface damp until germination. A clear cover helps, but remove it as soon as the first seedlings appear.

05Two different clocks

Days to germination and days to maturity measure different things. Germination is the wait from sowing to visible seedlings; maturity is the wait to the part you intend to harvest. A slow germinator is not necessarily a slow crop, and a fast germinator can still take months to flower.

This matters when planning a bed. A parsley that germinates unevenly may still be harvestable for months. A coriander that germinates in a week can bolt in another three. Read both numbers, then add what the packet cannot know: your light, your water, your slug pressure and the fact that a windowsill is not a field.

If germination is patchy, do not immediately sow again. Check temperature, moisture and depth first. Old seed, cold compost and a dry surface are more common causes than bad luck. A second sowing on top of the first usually produces a crowded, uneven row.

06The date, the lot and the seed count

Seed is a living product. Germination declines with age, heat and humidity, and the decline is not the same for every species. A “packed for” or “use by” date is not a guarantee, but it is a useful warning. If the seed is old, sow more thickly and expect a lower percentage to emerge.

The lot code is the producer’s traceability number. It matters if a packet fails badly or if you want to compare two batches. Write it in your garden notes alongside the sowing date. When a variety performs well, the lot code is how you find the same batch again.

Seed count is often a better value measure than packet weight. A gram of tiny seeds can be thousands of plants; a gram of beans is a handful. Compare the number of seeds, the germination expectation and the space you actually have, not the size of the envelope.

07What the packet cannot tell you

The packet does not know your last frost date, your soil temperature, your water pressure or how much shade the neighbour’s fence casts in June. It cannot tell you whether your compost is too rich for lavender or whether the slugs will find the basil before you do. Those are local observations, and they outrank the envelope.

It also cannot tell you whether the plant is worth growing. A variety that matures in a heatwave may be a poor choice for a cool, wet garden, even if the packet says it is easy. Grow a small trial before committing a bed. Keep a note of sowing date, germination, first harvest and the weather that shaped the season.

The packet is a starting contract. Your records are the renegotiation. After two or three seasons, you will know which dates, depths and varieties actually work on your site — and the packet becomes a reference rather than a rule.