Question
I have a citrus plant in my conservatory a small orange there is a sticky substance over all the leaves that also goes on the floor is there anything I can do and what causes it

Answer
Look closely at the stem of the plant.  See if you see small oval brown structures on the stem.  Or look on the undersides of the leaves for small green soft bodied insects.  Aphids and scale give off a sugary sticky substance called "honey-dew" when they feed.  You may also see some black mold growing on the leaves as well.  This is called sooty mold.  All of this is related to insect feeding.  You will have to treat the bugs, otherwise they will kill your plant and move to other plants.  You can do this with Safer Insecticidal Soap or Sevin.  You can also use heavy mineral oil and with a Q-tip coat each bug individually.  Last and best option is to use Bayer Advanced Tree and Shrub Insecticide that can be purchased from Home Depot.  You can use this insecticide only if the tree is not currently bearing fruit that you will want to eat. It takes about a week for the chemical to be taken up by the plant.  It is systemic and is poured on the soil. If all of this seems to not be the case, please respond back and we will look into another cause.  Good Luck.