Common Mistakes When Planting Spring Bulbs in Pots

Spring bulbs in pots look like the easiest job in the world in the catalogues: press them into compost, wait, and enjoy. Then spring arrives and you have a pot of floppy leaves and no flowers. Containers are a far tougher environment than open ground. Compost dries out fast, freezes solid in January, and holds only what you put in it. Most disappointments come down to depth, drainage, layering and watering. Get those four right and a modest pot will outperform a border.

Planting at the wrong depth

The old rule still holds: a bulb wants roughly two to three times its own height of compost beneath it. A 5cm crocus sits about 8–10cm down; a chunky 15cm daffodil needs 15–20cm below its base. Measure from the base of the bulb, not the tip, to the surface of the compost.

The usual version of this mistake is cramming bulbs into shallow compost because the pot looks generous from the outside. A pot 25cm wide but only 15cm deep will not take a proper layer of tulips. You end up with bulbs sitting 3cm under the surface, where they dry out, get pushed up by frost and send up weak shoots. Going too deep is rarer, but tall narrow pots that are mostly empty cause it; small bulbs under 20cm of heavy wet compost struggle to push through at all.

Whatever you plant, leave 3–5cm between bulbs and from the pot wall. Bulbs that touch are more likely to rot, and those pressed against the side get colder, wetter or drier than the rest.

Drainage problems that rot bulbs

Bulbs are storage organs, and they rot when they sit in water. In a container, water has nowhere to go unless you give it a route out.

• Choose pots with several drainage holes, not just one. A single central hole clogs easily with compost.
• Skip the thick layer of crocks. A handful of gravel or one broken piece over each hole is enough to stop compost washing out; a deep rubble layer simply raises the water table inside the pot.
• Stand pots on feet or bricks so they are not sitting in a puddle or a full saucer.
• Mix peat-free multipurpose compost with 20–30% horticultural grit or perlite. Never use garden soil in a pot.

If a pot has no hole, use it as a cachepot and stand a plastic pot inside. A drill and a masonry bit can solve the problem, but a hidden inner pot is quicker and safer.

Layering without a plan

Lasagne planting — stacking bulbs in layers in one pot for a long season of flowers — is one of the best tricks for containers. It also fails in predictable ways. Work from the biggest bulbs at the bottom to the smallest near the surface.

1. Large daffodils, tulips and alliums, 15–20cm deep
2. Hyacinths and smaller narcissi, around 10–12cm
3. Muscari and Iris reticulata, 7–8cm
4. Crocus, snowdrops and scilla, 5cm — just below the surface

The common errors are putting shallow bulbs deep and deep bulbs shallow, overfilling the pot, and mixing bulbs that flower months apart. A crocus layer that finishes in February is swamped by tulip foliage in April, and the roots of the larger bulbs disturb the smaller ones. Keep each layer to bulbs that flower within a few weeks of each other, and stop adding bulbs while you can still fit your hand in the pot to cover them with 3cm of compost.

Watering mistakes at every stage

Bulbs in containers need steady moisture from planting until the leaves die back, but how much changes dramatically through the season.

In autumn, water thoroughly at planting, then keep the compost just moist while roots form. Rain usually does this for pots left in the open; pots under a porch or against a wall may need a canful every week or two. Little and often is the classic error — a splash every few days wets only the top few centimetres while the bulbs below stay dust dry. Water properly, slowly, until it runs out of the drainage holes, then leave the pot alone. In winter, ease off and never let pots stand in a full saucer. Cold, wet compost is what rots bulbs.

Once shoots appear, demand rises steeply. Dry compost in March and April gives short stems, small flowers and dropped buds, which often gets blamed on bad bulbs. Water before the compost dries out completely, and keep going after the flowers fade. Those final weeks, while the leaves are still green, are when the bulb stores energy for next spring. Deadhead spent flowers so the plant does not waste effort on seed, but leave the foliage alone. Cutting it back early, or tying it in knots, costs you next year's display.

Compost, feeding and pot size

A pot is a small, sealed system. Everything the bulb needs must be in the compost or added later, and one season of bulbs uses up most of what a fresh mix offers. Feed with a balanced liquid feed as shoots emerge, then switch to a high-potash tomato-type feed once buds show, continuing until the leaves die down. High-nitrogen feeds give you fat leaves and few flowers.

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