If you've dug up a garlic plant and found one solid clove instead of a split bulb, the plant didn't fail — it just never got the signal to divide. Garlic needs an extended cold spell to turn a single planted clove into a multi-clove bulb. In most of temperate New Zealand that winter cold is reliable, so when bulbs don't form here the cause is usually something you control: a planting that went in too late, or soil too poor to size a bulb. That single clove is called a "round," and it's completely usable — but here's why it happened and how to get a proper bulb next time.

The most common reasons — ranked

1. Planted too late. This is the number-one cause. Garlic wants to go in during early-to-mid autumn — April into May — so it can establish roots and bank the winter cold before spring warmth and lengthening days push it into bulbing. A clove that goes in during June or July misses that runway and often stays a round.

2. Starved or crowded plants. Garlic is a hungry crop. Poor, unfed soil or cloves packed too tightly produce small, single-layer bulbs even when the timing is right. It wants rich, free-draining soil and 10–15cm of space between cloves.

3. Harvested too early. Garlic needs roughly seven to eight months in the ground. If you lift before the lower third to half of the leaves have yellowed off, the bulb simply hasn't finished dividing and sizing.

4. Wrong seed or wrong variety. Supermarket garlic is often treated with a sprouting inhibitor and can carry disease, and a variety bred for a much colder or warmer region will underperform. Plant certified seed garlic of a type proven in NZ conditions.

5. Not enough winter cold. This one sits last here, not first — temperate winters usually deliver plenty of chilling. It matters far more in warm northern gardens. If you're in the mildest, most coastal end of the zone and you've ruled out everything above, an unusually warm winter could be the reason, but it's rarely the first thing to suspect here.

Check your timing against the planting window

The planting window for garlic runs April through May, with harvest landing in November–December. If your cloves went in later than that, timing alone is the most likely explanation — nothing else needs to be wrong. Get next year's crop in by early May and you remove the single biggest cause in one move. You can see the full month-by-month picture on the NZ Temperate planting calendar.

What to do now

Don't panic-lift the rest of the bed. Wait until the lower leaves have properly yellowed, then dig one plant to check before harvesting the lot. A round is still good garlic in the kitchen — and it's excellent seed. Replant your best rounds next autumn and they'll often grow into large bulbs, because they go into the ground already carrying a full season's stored energy.

What to change next season

  • Plant by early May so the crop banks the winter cold and has the full season to size up.
  • Enrich the bed with compost and well-rotted manure before planting — garlic can't be rescued with a late feed once bulbing starts.
  • Space cloves 10–15cm apart and mulch to keep weeds from competing.
  • Start with certified seed garlic of a proven variety rather than a supermarket bulb.

Get those four right and you'll get full, split bulbs reliably — this is one of the more forgiving zones for garlic once the timing is sorted.

Planting garlic this season? See When to Plant Garlic in Canterbury NZ for the cooler-zone timing, or explore the full NZ Temperate Planting Calendar →.