Why spring starts in autumn

The most colourful fortnight of the gardening year is decided long before it arrives. Every daffodil and tulip you admire in April was quietly planted the previous autumn, sitting in cold, dark soil through the worst of the winter. It is one of the most rewarding jobs on the plot: a couple of afternoons of work in September and October, and then months of flowers in return.

Borders are the perfect place for it. Unlike a lawn, you are not mowing around bulbs, and unlike pots, the soil stays cool and moist. Planted well, a border can carry colour from February snowdrops and crocus right through to late May tulips, just as the herbaceous plants are waking up. The trick is not complicated, but it does come down to three things: depth, grouping, and timing.

Plant at three times their depth

This is the rule that matters more than any other. Plant a bulb at roughly three times its own height, measured from the base of the bulb to the surface of the soil. A fat daffodil bulb about 5cm tall wants to sit around 15cm down. A small crocus corm, barely 2cm, only needs 5cm or so. Tulips, being tall and top heavy, are happiest 15 to 20cm deep.

It is worth resisting the urge to go shallower. Bulbs planted too near the surface tend to:

• Push themselves up out of the ground as roots develop
• Flop over once the flower heads fill with rain
• Get lifted and eaten by squirrels, mice and pheasants
• Dry out in a warm spell before they have rooted properly

Deeper planting keeps them cool and anchored, and it encourages strong, sturdy stems. It also hides the bulbs from curious wildlife. Narcissus and daffodil bulbs are distasteful to most animals, but tulips are a favourite, so a good deep hole is genuinely useful protection.

If you have heavy clay, dig the hole a little deeper still and drop a handful of horticultural grit or sharp sand in the bottom. Bulbs rot in waterlogged ground, and a free-draining pocket is cheap insurance. Set them the right way up, pointed end skywards, firm the soil back gently and water them in.

Group in odd numbers, not straight lines

Nothing gives away a planted border faster than a neat row of bulbs. Nature does not do arithmetic, and neither should you. The classic advice is to plant in odd numbers: groups of five, seven, nine or eleven. Odd numbers read as accidental to the eye. Even numbers, especially in pairs, tend to look deliberate and slightly stiff.

Aims for drifts rather than dots. Take a handful of bulbs, toss them gently onto the soil, and plant them exactly where they land, spacing them about two bulb-widths apart. Vary the spacing a little within each group. Some slightly closer, one or two further out. That slight irregularity is what makes a planting look as though it has been there for years.

If you have the space, go bigger than feels sensible. A drift of thirty daffodils running behind a shrub is far more striking than five bulbs dotted about. Odd numbers work at every scale, from a small group of five tulips between perennials to a long informal ribbon along the back of a border.

Choose for a long season

Daffodils and tulips are the backbone, but you can stretch the show considerably. Bulbs flower in sequence, so layering them gives you weeks rather than a fortnight.

• February to March: snowdrops, winter aconites, early crocus
• March to April: miniature and species daffodils, grape hyacinths, scillas
• April: tall daffodils, fritillaries
• May: tulips, alliums

Within the daffodils, look for a mix of early, mid and late varieties, and include a few of the small species types for pots and the front of the border. With tulips, the taller late-flowering sorts give you the biggest impact in May, just as perennials are pushing through and hiding the yellowing bulb foliage.

Plant daffodils from September to November, as early as you reasonably can. Leave tulips until November or even early December. A spell of cold in the ground before growth starts helps them flower well, and planting tulips late reduces the risk of disease in wet autumn soil.

Layering and aftercare

You can plant two or three layers in the same patch of border, a technique often called lasagne planting. Put the deepest, latest bulbs, usually tulips, at the bottom, then a layer of soil, then daffodils, another layer of soil, then small bulbs like crocus or muscari near the surface. The foliage comes up at different heights and times, so nothing gets smothered.

Mark where you have planted. A few short sticks or a scatter of grit saves you slicing through sleeping bulbs with a fork in February. Water the ground well after planting, and then largely leave it alone.

Once the flowers fade, deadhead them so the plant does not waste energy on seed, but leave the foliage for at least six weeks. That green growth is feeding next year's bulb. Hide it behind emerging perennials, or grow bulbs among plants that will cover the gap. A light feed with a high-potash fertiliser at this point helps them fatten up for the following spring.

Tulips are the exception to all this patience. Many are best treated as annuals in a British border, lifted and replaced each year, especially in heavy or wet soils. Daffodils, on the other hand, will naturalise happily and multiply, giving you more colour every spring for very little effort indeed.