Farming is a skill in which players plant seeds and harvest crops. The crops grown range from vegetables, herbs and hops, to wood-bearing trees, cacti, and mushrooms. The harvested items have a wide variety of uses, and are popular for training 
Herblore and 
Cooking.
Training Farming
During your Farming training, you will be progressing the skill by planting an herb seed, a fruit tree seed, and a regular tree seed and harvesting the contents for XP. Understand that tree seeds must be used on a plant pot to create a sapling of that tree. You are unable to directly plant tree seeds into tree patches.
Level 1 to 9
From levels 1-9 you will be planting Potato Seeds. Alternatively, you can just rake the patches since the early XP is minuscule anyways. Either way both methods will be incredibly fast.
Level 9 to 26
From levels 9 to 26 you will be planting Guam herbs. It should only take one or two farming runs to get these levels, just make sure you're utilising all 5 of the herb patches that are shown.
Level 26 to 32
From levels 26 to 32 you will be planting Harralanders. This portion of training will also only take one or two farming runs.
While you are planting your Harralanders, level 27 Farming unlocks the ability to plant the lowest level fruit tree, apple trees. From this point forward, while you are planting your herbs you will simultaneously be planting the highest level fruit tree you can.
Level 32 to 44
From levels 32 to 44 you will be planting Ranarr herbs.
At level 33 you unlock the second lowest fruit tree - the Banana tree.
At level 39 you unlock the third lowest fruit tree - the Orange tree.
At level 42 you unlock the next fruit tree - the Curry tree.
Method 1: Fastest XP
Level 44 to 50
From levels 44 to 50 you will be planting Irit Herbs.
You will also be planting Curry Trees in your Fruit Tree patches.
You are now able to plant Maple Trees. This adds a few more patches to your farming route as you are now able to plant Trees in Tree Patches. Simply search "tree" in the Teleport Nexus to be shown a list of Tree Patches.
Level 50 to 62
From level 50 to 62 the herb you will be planting are Avantoes.
Pineapple Fruit Trees can be planted at level 51.
Maple trees will be planted until level 60. From level 60 onwards you are now able to plant 
Yew Trees.
Level 62 to 85
From level 62 to 85 you will be planting the highest level Herb, Fruit Tree, and Regular Tree you can.
These will include the following Herbs:
Cadantines from levels 67 to 73.
Lantadymes from levels 73 to 79.
Dwarf Weeds from levels 79 to 85.
The following Fruit Trees:
Papaya Trees from levels 57 to 68.
Palm Trees from levels 68 to 99.
The following Trees:
Yew Trees from levels 60 to 75.
Magic Trees from levels 75 to 90.
Level 85 to 99
From levels 85 to 99 you will be planting Torstols as your Herb.
Method 2: Overload Supplies
Level 44 to 56
From levels 44 to 56 you will be planting Irit Herbs. This Herb is an ingredient in creating Super Attack Potions.
Level 56 to 67
From levels 56 to 67 you will be planting Kwuarms. This Herb is an ingredient in creating Super Strength Potions.
Level 67 to 73
From levels 67 to 73 you will be planting Cadantines. This Herb is an ingredient in creating Super Defence Potions.
Level 73 to 79
From levels 73 to 79 you will be planting Lantadymes. This Herb is an ingredient in creating Magic Potions.
Level 79 to 85
From levels 79 to 85 you will be planting Dwarf weeds. This Herb is an ingredient in creating Ranging Potions.
Level 85 to 99
From levels 85 to 99 you will be planting Torstols. This Herb is an ingredient in creating Overloads.