How does Flower Bulb sizing work and what should I look for?

Created by Kinsey Harris, Modified on Mon, 05 Dec 2022 at 03:46 PM by Kinsey Harris

Since most bulbs come direct from growers and farms in Holland, bulb sizes within the industry are usually given in centimeters and are usually labeled as such by the "cm" notation to indicate the circumference of a bulb (note there are 2.54 centimeters in an inch.)

The size of the bulb is expressed as the girth of the bulb in centimeters. In other words a 10-12 tulip bulb is between 10 and 12 centimeters in girth at its broadest point. The bigger the bulb, the more blooms you will get and the larger they will be. Bulbs will also grow larger in the ground after blooming.

To measure a bulb, wrap a tape measure around the widest part of the bulb.

The following chart provides a guideline as to what are the minimum and maximum sizes of fall planting bulb varieties.

Variety	Top size		Minimum acceptable size		Notes
	In centimeters	In inches	In centimeters	In inches
Tulips	12/+ cm	4.72	10 cm	3.94
Narcissus and Daffodils	16/+ cm	6.3	12 cm	4.72
Hyacinths	19/+ cm	7.48	14 cm	5.51	Top size hyacinths are usually reserved for indoor forcing. In the garden look for hyacinths size 15/16 cm. Larger hyacinths have a tendency to fall over from the weight of the flower.
Large Flowering Crocus	9/+ cm	3.54	7 cm	2.76
Specie or Snow Crocus	5/+ cm	1.97	4 cm	1.57
Dutch Iris	9 cm	3.54	7 cm	2.76
Specie Iris	6 cm	2.36	4 cm	1.57
Large Allium	20/+ cm	7.87	19 cm	7.48	Includes following varieties: Giganteum, Lucy Ball, Stipitatum, Globe Master
Medium Allium	14/+ cm	5.51	12 cm	4.72	Include following varieties: Aflatuense, Christophii, Karataviense, Rosenbachianum, Schubertii, Ivory Queen
Small Allium	4 to 6 cm	1.57 - 2.36	4 cm	1.57	Includes following varieties: Moly, Ostrowskianum, Neapolitanum, Sphaerocephalon
Fritillaria Imperial	24/+ cm	9.45	22 cm	8.66
Amaryllis	34/+ cm	13.39	24 cm	9.45
Jumbo Amaryllis	42/+ cm	16.54	n/a	n/a	Only a few varieties of Amaryllis grow larger than 34 cm
Paperwhite Narcissus	17/+ cm	6.69	14 cm	5.51	Ask your local retailer for Jumbo paperwhites.
Oriental Lilies	18 cm	7.09	16	6.30
Asiatic Lilies	14/+ cm	5.51	12 cm	4.72