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The four species must be of a reasonable size, not too small. If they are so dried out there is no moisture left and they have turned white, they are invalid. To keep hadasim and aravot fresh, they can be left in water or a sealed bag.
Ideally, a lulav is straight. If a lulav bends forward or sideways into a semicircle, or if it has completely dried out, it is invalid. The leaves of the lulav should tightly encase the spine. If the leaves have spread and hardened making it impossible to gather them together and pull them close to the spine, the lulav is invalid.
A hadas must live up to the Torah’s description: “boughs of leafy trees” (anaf etz avot). This is limited to a myrtle with threefold leaves that almost look braided and that cover the stem, making it look like a thick branch (anaf aveh).
If the top of an arava breaks off, the arava is invalid because it has lost its beauty. However, if only the top leaf falls off but the stem is undamaged, it is kosher.
Just as with all fruits, there are multiple varieties of etrog. Some are large and some are small, some are yellow and some are green, but all are kosher.
Every etrog starts out with a pitam (blossom-end), but usually it dries out and falls off when the etrog is very small. Such an etrog is absolutely kosher without a pitam, as this is how the fruit grows. However, those etrogim which retain their pitam must be treated gently, because if an etrog falls and the pitam breaks off entirely, the etrog is invalid.
An etrog with a very strange spot is invalid. In contrast, the commonly-found gray or brown spots (bletlakh in Yiddish) do not invalidate it, as they are normal. These spots are usually caused by the etrog’s contact with leaves and branches, which lightly scratch it. The scratch releases a liquid which solidifies on the outside of the etrog. Even after an etrog has been picked, this liquid may be released if it is damaged and form a brown spot, which makes the etrog less beautiful. (For this reason, people generally wrap an etrog in flax or place it in styrofoam mesh.) If an etrog falls or suffers any trauma, it should be rinsed off to remove the released liquid, thus preventing a spot from forming.
