Start With the Numbers, Not the Picture

The front of a seed packet is a sales pitch: a glossy courgette, a flawless tomato, a marigold the colour of a sunset. Turn it over and you find something far more useful — the grower's manual. Sowing depth, spacing, hardiness and days to maturity are all printed there, usually in six-point type that nobody reads until something goes wrong.

Those four figures tell you nearly everything you need to know about how a plant wants to be treated. Get them right and you will lose fewer seedlings to rot, thin your rows once instead of twice, and stop wondering why your parsnips came up bent and stunted. Read them properly and a seed packet becomes a planning tool for the whole plot.

Sowing Depth: Roughly Three Times the Seed's Width

The old rule of thumb holds up well: bury a seed about two to three times its own diameter, and no deeper. Too deep is the most common mistake on a smallholding, because a seed has only so much stored energy. If it has to push through five centimetres of cold, wet soil to reach the light, it will usually rot before it gets there.

In practice, that means:

• Large seeds — broad beans, sweetcorn, courgettes, sunflowers — go 3–5cm down.
• Medium seeds — beetroot, chard, spinach, peas — about 2cm.
• Small seeds — brassicas, tomatoes, peppers, most herbs — barely 1cm.
• Tiny seeds — lettuce, celery, poppies, foxgloves — pressed into damp compost and left uncovered, because several of them need light to germinate at all.

Two practical tweaks. If you are direct-sowing something fine, mix the seed with a little dry sand so it trickles out evenly instead of landing in one clump. And if the spring soil is dry, sow a fraction deeper than the packet says, water the base of the drill first, then cover and firm gently.

Spacing: Measuring Now Saves Thinning Later

The spacing figure on a packet is the final spacing — the room a mature plant needs — not the distance at which to scatter seed. Use it to choose your module size when raising plants under cover, and to know how hard to thin a direct-sown row.

Typical final spacings for a UK plot look like this: carrots 5–8cm, beetroot 10cm, onions 10cm, lettuce 25–30cm, brassicas 45–60cm, courgettes around 90cm, and tomatoes 45–60cm in a greenhouse border or grow bag. Between rows, allow 30–40cm if you plan to hoe by hand, and wider where you need to walk and harvest.

Thin in the evening when the soil is damp, nipping the unwanted seedlings off at soil level with scissors rather than pulling them, which disturbs the roots of the plants you are keeping. Eat the thinnings — baby beet leaves and young carrot thinnings are a genuine crop in their own right. On a smallholder's plot, the spacing figure is also your cue for intercropping: quick radishes or salad leaves between slow parsnips, harvested long before the main crop needs the room.

Hardiness: What the Label Says About Frost

This is the section most often skimmed, and the one that decides whether a sowing lives or dies. Seed packets usually sort crops into three groups.

• Hardy — tolerant of frost. Broad beans, parsnips, carrots, onions, most brassicas, spinach and chard can be sown direct from early spring, and several will overwinter happily.
• Half-hardy — damaged or killed by frost. Tomatoes, courgettes, sweetcorn, French and runner beans, basil. Sow under cover, or direct-sow only once the last frost has passed.
• Tender — need real warmth, generally a minimum of 10–12°C. Aubergines, peppers, sweet potatoes and okra want a long season and a polytunnel or greenhouse in most of the UK.

Work out your own last-frost date rather than trusting a national average. A frost-pocket valley can run a fortnight behind a mild coastal strip only a few miles away. If you do not know yours, ask the gardener who has been on the neighbouring plot the longest. Then count back six to eight weeks for indoor sowings, and keep fleece, cloches or a cold frame ready for late surprises.

Days to Maturity: Planning Backwards From Dinner

Days to maturity is the most flexible figure on the packet, and the most useful for planning. First, check what it counts from: tomatoes and brassicas are usually measured from transplanting, while roots and salads are often measured from sowing. That difference can be a month.

Then work backwards. If you want Brussels sprouts for Christmas, look for a variety listed at 100–150 days from transplanting and sow to suit. For salads, radishes and spinach, ignore the calendar and sow a short row every two to three weeks for a continuous supply.

Treat the number as a guide for a decent season, not a promise. A cool, cloudy June can add a week or more; a hot, dry August can bring harvest forward but at the cost of quality. On a northern or upland plot, long-season crops such as outdoor peppers and melons may never quite finish — choose the shortest-dated varieties you can find, or give them protection.

The Fine Print Worth Reading

A few last details repay a moment's attention. The sow by date is a germination guide, not a use-by date; seed kept cool, dark and dry will often perform well past it. The germination percentage tells you how thickly to sow — 70 per cent means sow a little more generously. F1 hybrid seed is vigorous and uniform, but seed saved from it will not come true. Pelleted seed, coated in a clay jacket, makes small or irregular seed far easier to space accurately.

Finally, do what good growers have always done: write on the packet. Date sown, depth used, how many came up, how they cropped. After two or three seasons that scribbled envelope is more valuable than any table, because it describes your soil, your weather and your plot — which is the only thing that really matters.