Needs to be updated:

 

 

 

 

First, ALWAYS use supercompost. You will get much better harvests, and it decreases the chance for disease tremendously. Since you can't be everywhere at once, this is very important. Pineapples are easy to pick in the Karamja jungle just north of the dungeon to Iron Dragons. They can also be bought from Charter Ship crew members; two are conveniently located just south of Catherby Bank. Jangerberries are on the ogre island just a short walk east of Castle Wars. Stock up on these while you wait for your crops to mature.

 

 

 

 

With the new shop update, it is no longer possible to buy Pineapples from the Charter Ships.

 

 

 

You can, however, still buy them from the Grand Tree, which is your best bet if you want to buy them. (10 in stock, not infinite)

There are 2 places in grand tree (same floor) were they sell 10 pineapples.

 

The general store in front of Catherby bank also sells 40 pineapples per day if you talk to him instead of trade him.

Thanks, and done.