On Shavuot, one may top up the water in the vase if necessary, but the ratio of the new water must be less than half of the total. One may certainly not replace the existing water.
A potted plant should not be moved due to two concerns – Muktzah and aiding plant growth. [In principle, these issues are subject to differing Halachic opinions and other variables.] If the potted plant accidentally overturns, or some soil spills out, it should be left alone. [If doing so will create a hindrance or inconvenience, a Rav should be consulted.]
For practical purposes, a potted plant should generally be treated as attached to the ground. Therefore, one may not water it at all or detach any of its leaves or branches. One may not lean on a potted tree or shrub, move it with his hands even ever so slightly, place anything in its branches, or remove anything caught in its branches.
Flowers, branches or leaves that were detached (regardless of the cause) on Shavuot are Muktzah. The same is true even if there is just a doubt whether it became detached on Shavuot. It goes without saying that they are Muktzah when still attached to the ground.
One may smell flowers and plants on Shavuot – even if still attached to the ground (and hence Muktzah). One should remember to make the appropriate Brachah. However, one may not smell attached fruits.
Candle-Lighting
Prior to candle-lighting, one should give Tzedakah on Erev Chag for Chag itself. Candle-lighting is at 7:09pm. The Brachot are Shel Yom Tov and Shehecheyanu. [If eating out, one should ensure that some practical benefit is derived from the candles after Chag begins.]
Since it is Chag, if one neglected to light at the proper time, one may – and should – light candles on Chag itself, from a pre-existing flame.
When a man is required to light candles, he does not recite Shehecheyanu, as he will be doing so in Kiddush. [Therefore, it is best that he lights candles right before Kiddush, so that his Shehecheyanu is linked to both.] Similarly, if a woman needs to recite her own Kiddush, she does not recite Shehecheyanu, as she already did so at candle-lighting.
