Of course any dahlia may be cut and displayed in a vase. However, to achieve the very best displays there are a number of principles to follow.
The National Dahlia Society Judging rules are an excellent starting point to understanding what to aim for. To produce the very best quality blooms one should grow from rooted cuttings each year as blooms from tubers do not have the quality of petal density, petal formation, nor colour clarity or intensity.
1. As a general principle anything that detracts from the perfection of a bloom, or an exhibit, is a "fault" and the seriousness or otherwise of the fault depends upon the degree of imperfection. Whereas a damaged, eaten, or malformed floret at the rear of the bloom does little to detract from its beauty and overall perfection, that same defect on the face of the bloom, one which mars its beauty, would be considered a very serious fault. In judging an exhibit the following faults must be evaluated accordingly.
2. It is a VERY SERIOUS fault if a bloom:
a. Is malformed
b. Faces downwards (less than 45 degrees).
c. Has been badly damaged, eaten, bruised or otherwise blemished on the face of the bloom.
d. Has limp drooping florets.
e. Has had an excessive number of florets removed.
f. Has an open (daisy-eyed) centre (double-flowered cultivars only).
g. Has a centre that is hard and green, large and undeveloped or badly distorted.
h. Has oval or isolated centres.
i. Has a gap created by a missing outer floret.
j. Seriously departs from the standard formation of the class of dahlia for which the class calls.
3. Faults of a LESSER DEGREE, in accordance with the amount by which the fault detracts from the perfection of a bloom, are as follows:
a. Irregular or oval outline of bloom.
b. Has sunken centres.
c. Uneven, irregular, or unbalanced formation.
d. Florets lacking freshness or which are bleached, discoloured, faded, eaten, bruised, malformed or otherwise blemished on the rear of the bloom.
e. Florets that have been removed.
f. Stems which are bent, weak, short jointed, thick and out of proportion.
g. Uneven or inconsistent colouring, but this does not apply to bi-coloured or variegated blooms.
h. Shallow blooms, i.e. those lacking depth or fullness.
i. Blooms which are either immature or past their best.