Why bulb size is crucial 

When choosing flower bulbs, we often focus on the colour and shape of the flower on the packaging. But if you really want to succeed — in your garden or indoors — it pays to look beyond the surface. One of the most important yet frequently overlooked factors is bulb size. At The Bulb Farmers, our farmers select bulbs not just by variety, but specifically for their optimal size. In this article, we explain exactly what bulb sizes are, how they're measured, and why the biggest bulb isn't always the best choice. 

So what exactly is a bulb size? 

In the world of flower bulbs, size isn't determined by weight or height, but by the circumference of the bulb at its widest point. This circumference is expressed in centimetres. When you see the label 'Size 12/+' on a package or in an online shop, it means the bulbs have a circumference of at least 12 centimetres. This standardised sizing system ensures that farmers and consumers alike know exactly what to expect. 

Why does size matter so much? 

A flower bulb is essentially an underground storage room. Everything the plant needs to grow and bloom — the energy, the nutrients, and even the flower bud in its earliest form — is already packed inside the bulb. 

• Larger bulbs generally hold more reserves. This often results in sturdier stems, larger flower heads, or even multiple flowers per bulb (as seen in certain narcissi).
• Optimal bulbs strike the perfect balance between maturity and growing power. 

The myth of 'bigger is always better' 

It's a common misconception that the largest bulb size always delivers the best results. With some varieties, a bulb that's too big can actually work against you. 

• The 'over-the-hill' bulb
  Some flower bulbs reach a point where they've used up their maximum growing power. The bulb may be impressively large, but its vitality is on the decline. This can lead to less spectacular flowers or a greater susceptibility to disease.
• Top-heavy
  With varieties that produce very large blooms — think certain dahlias or lilies — an extremely large bulb can result in a flower so heavy that the stem snaps without extra support.
• Value for money
  The very largest sizes are often exponentially more expensive, while the visual difference in the garden is minimal compared to the 'highest standard size'.
  

That's why our farmers choose the most suitable size: the size that guarantees a stunning display, without the downsides of an 'exhausted' giant bulb. 

Common sizes per variety at a glance 

To give you a sense of what 'good' looks like, here are some guidelines for popular varieties. 

• Tulips: for an impressive show in the garden, size 12/+ is the gold standard. Smaller sizes (10/11) are often used for naturalising or planting in pots.
• Narcissi: these are often measured in 'round sizes' (e.g. 12/14 or 14/16). Larger sizes here often produce two or three flower stems per bulb.
• Dahlias: here we don't talk in centimetres of circumference, but in 'grades' (Grade I or II). Our farmers select only Grade I tubers for the most exuberant summer blooms.
• Alliums: sizes vary enormously here. A small Allium Sphaerocephalon is perfectly happy at size 5/+, while the magnificent Allium Globemaster needs bulbs of 20/+ centimetres. 

Straight from the farmer: your quality guarantee 

Because we work directly with the source, we cut out a very long chain. This has three major advantages when it comes to bulb size: 

• Freshness: the bulbs don't dry out in warm warehouses, so they retain their size and firmness.
• Quality control: the farmer personally ensures that only bulbs meeting the strictest standards are delivered.
• Honest advice: we won't sell you 'giant bulbs' if we know that a slightly smaller size produces a healthier plant.

In short: when it comes to choosing bulbs, you don't need to reach for a tape measure. Our farmers have already done that work for you — so all you need to do is plant and enjoy the results.