When and How Deep to Plant Tulip Bulbs in Autumn

Wait until the ground is cold, not just until autumn arrives

Tulips are the last bulb to go in. Daffodils want six to eight weeks of root growth before hard frost, so they go in early autumn, but tulips want the opposite: soil that has already dropped to around 55F (13C) and is still falling. In practice that is mid to late autumn, and in a mild garden it can be as late as the first hard frosts.

The reason is disease. Tulip fire, a botrytis that comes in on infected bulbs and overwinters in the soil, gets going in warm damp ground. A bulb planted into soil still holding summer heat sits there for weeks before it starts rooting, and that idle warm period is exactly when the fungus takes hold. Cold soil sends the bulb straight into root growth and gives the fungus nothing.

Late planting has almost no cost. A tulip bulb already contains next spring's flower, fully formed inside it. It does not need a long autumn to build one. Bulbs planted just before the ground freezes still root, still flower, and often flower a few days later than early-planted ones, which is useful if you want to stretch the display.

Plant three times the height of the bulb, and then a bit more

The standard rule is to cover a bulb with soil to three times its own height, which for a full-sized tulip means a hole six to eight inches (15 to 20 cm) deep. Most disappointing tulip beds are planted at four inches because that is as deep as a hand trowel comfortably goes.

Depth does three separate jobs. It anchors the stem, so a tall tulip in wind leans instead of snapping at ground level. It keeps the bulb at a steadier temperature, which stops it starting into growth during a warm spell in late winter. And it puts the bulb below the zone where the plant makes small offset bulblets, which is the main way a tulip planting turns into a patch of leaves with no flowers.

If your soil is heavy clay and you are nervous about rot, do not compensate by planting shallow. Plant at full depth and improve the drainage instead: dig the whole area a spade deeper and work in grit, or raise the bed. A tulip sitting in a deep hole full of standing water will rot, but so will one in a shallow puddle.

1. Dig an area, not individual holes Take out the whole planting area to eight inches (20 cm) and set the soil aside. You will place bulbs far faster and far more evenly than by punching one hole at a time, and you can see instantly if any part of the base is a wet hollow.
2. Set the bulbs pointed end up, four to six inches apart Four inches (10 cm) apart gives a dense block of color; six inches (15 cm) suits bulbs you intend to leave in the ground. Do not let bulbs touch each other, because a single rotting bulb will take its neighbors with it.
3. Backfill and firm gently Return the soil, break up any clods and firm with the flat of your hands. Air pockets around a bulb dry the new roots. Do not stamp it down, which compacts heavy soil into a pan that holds water.
4. Water once, then leave them One thorough watering settles the soil and triggers rooting. After that, autumn and winter rain is enough. Bulbs do not need to be kept moist through winter and will rot if you keep watering a bed that never dries.

Plant a few inches deeper than standard, around ten inches (25 cm), if you want the bulbs to persist for several years. Deep bulbs make fewer offsets and stay full sized for longer, at the cost of emerging a little later in spring.

Squirrels, mice and voles dig up what you just planted

Squirrels are not hunting tulips by smell so much as investigating freshly disturbed ground. The single most effective thing you can do is leave no sign that you were there: rake the surface flat, remove the papery brown bulb tunics that flake off during planting, and water the bed so it settles and looks like the rest of the garden.

Where the pressure is serious, a physical barrier is the only reliable answer. Lay a sheet of galvanised wire mesh with half-inch (1 cm) squares flat over the planted area, pinned down and covered with an inch of soil or mulch. Shoots come up through the mesh in spring; paws do not go down through it. Chicken wire with larger holes works against squirrels but lets mice through.

Voles are a different problem, because they eat bulbs from below during winter rather than digging them out in autumn. If bulbs vanish underground and leave nothing behind, line the planting hole with grit; the sharp edges deter tunneling. Daffodils and alliums are toxic to rodents and are left alone, which is why a bed of pure tulips takes more damage than a mixed one.

Where they will actually be happy

Full sun and sharp drainage. Tulips evolved on dry mountain slopes with cold wet winters, hot dry summers and gritty soil, and the closer your bed is to that, the longer they last. A hot, well-drained bank at the foot of a south-facing wall is close to ideal, and a shaded bed that stays damp all summer is the fastest way to lose them.

Avoid planting into ground that has been heavily manured or fed with high-nitrogen fertilizer. Rich, soft growth is more prone to fire and to flopping. If you want to feed, a scatter of bone meal or a balanced granular feed worked into the planting area is enough, and it matters far less than drainage does.

Do not replant tulips into a bed where tulips showed fire last spring. The fungus persists in the soil on the debris of infected bulbs. Move to fresh ground and leave that bed three years before growing tulips there again.

Record where they went

Tulips are invisible for six months of the year, and every gardener eventually puts a spade through a dormant clump. Note the planting date, the depth you actually used, how many bulbs went into each spot and roughly where the block sits relative to something permanent such as a path edge or a shrub.

The depth note is the one that pays. Next spring, when one block comes up strongly and another comes up thin, the difference is usually depth, drainage or planting date rather than the bulbs themselves. Without the record you are guessing; with it you know which corner of the garden to trust for the following autumn.