A lot of us know to wet the reed before playing but do we know why we need to.
It's basically to lessen the stiffness and increase the mass of the reed for playability and to lower the vibrating frequency of the reed to lessen high frequency squeaking.
The reed soaking doesn't really need to be overdone, just a minute or so in a cup of water or whatever and unless the weather conditions are unusual that should usually be enough for a playing session.
For those who like Science
http://koppreeds.com/virtues.html
A young bassoonist typically learns in the first lesson that the reed is not expected to vibrate until it has been thoroughly soaked. But why is this so? Scientists have explained that this soaking (or hydration, as they prefer to call it) has important effects on the vibrational characteristics of even a simple rectangular section (a clarinet reed blank, for example) of Arundo donax, tending to lessen the stiffness and lower the vibrating frequency. When a piece of cane is made into a finished bassoon reed, additional effects of hydration come into play.
Casadonte carried out an experiment to measure a vibrational difference between unsoaked and soaked Arundo donax. He first clamped a dry, rectangular sample of Arundo donax and plucked it, obtaining a frequency of 269 Hz. When he soaked the cane sample and repeated the experiment, the frequency dropped to 220Hz. A physicist would say that the modulus of elasticity drops exponentially (that is, the cane becomes more flexible) as the reed is saturated.28 It also gains in mass, as explained below.
Double reeds are subject to additional physical forces. In the special case of a bassoon reed, the swelling of soaked tissues causes the reed's tip to pucker and the aperture to open to a functional dimension.
When a bassoon reed is hydrated, "free" water is stored within the cellular cavities and vascular tissue capillaries. According to Casadonte, the degree of swelling in a clarinet reed, taken new from its box and then fully hydrated to a level suitable for performance, is greatest in the radial (inside-to-outside) dimension: 16.8%. The reed also swells 7.5 % in the tangential (left-to-right) dimension, and 4.5% in the longitudinal (tip-to-butt) dimension. The weight or mass added by free water is 3.75 %.29 We can assume that the degree of swelling is somewhat less in a bassoon reed, which is gouged thinner; it thus contains a higher proportion of sclerified cells, and absorbs less water.
When the bassoon reed is allowed to dry, the tip aperture will often become partly or fully closed. But hydrating (fully soaking) the reed causes the blades to swell in thickness, increasing the tension and restoring the tip aperture to the correct degree of openness, a critical requirement for correct vibration of the reed. This additional effect occurs because the tip of the reed is thereby placed under additional tension.
Some tension is present in the bassoon reed even before it is soaked. What might be called "dry" tension arises from (1) the deformation of the cane's natural arc into a flatter arc at the reed's tip, and (2) the deformation of the natural arc into a much tighter arc at the back of the blade.30 Hydration brings about two new effects that might be called "wet" tension: (3) the hydrated blades increase in thickness; given that movement of each blade is constrained by its contact with the other blade, the swollen blades can only expand by assuming a higher arch. In a secondary effect, (4) the hydrated tube of the reed swells against the brass adjustment wires, and the resulting pressures further influence the tip aperture.
Sources of Tension in Bassoon Reed Blades
"Dry" tension is always present, the result of:
Flattening of cane's natural arc at the reed tip
Rounding of cane's natural arc at the reed tube
"Wet" tension occurs when the reed is soaked, so that:
Blades swollen with water expand into a higher arc
Tube swollen with water exerts pressure against wires, affecting tip aperture
To understand more about the hydration process of the bassoon reed, we need to know a few details of the chemistry of Arundo donax. According to Casadonte, different researchers analyzed five different stems of Arundo donax, with the following results: 42-50% cellulose, 20-24% hemicelluloses, and about 10-20% lignin, ash 4%, silica 1-2%.
Aside from the "free water" stored in a hydrated reed (as described above), a separate quantity of water is bound to the cellulose-hemicellulose-lignin matrix "more or less permanently." This "bound water," as Casadonte termed it, comprises 5.98% of the weight of the clarinet reed.
The amount of bound water varies slightly with changes in atmospheric pressure. As pressure increases, hydration is increased, and vice versa. Casadonte found that swelling due to bound water could reach .75% in the radial dimension, .63% in the tangential dimension, and .4% in the longitudinal dimension.31 (Over its useful life, the reed gradually loses hemicellulose; this loss decreases the amount of bound water that can be stored. This phenomenon is discussed below.)
Types of Water Retention in Bassoon Reed Cane
"Free" water is added each time the reed is soaked, increasing tension in the blades
"Bound" water is always present; the amount decreases as the reed ages