How to keep plants at 100% health

Planting & Harvesting in your House in Runes of Magic
the basics:
Be careful to plant the type of seed in the correct type of pot. (ie herb seeds like rat tail rattan must be planted in the Mayan herb pot or higher level herb pots(even better)(Wood seeds in Flowery Pot, Ore seeds in Seawave pots). Keep a record of the exact time and day that you planted the seeds. From that time, you know when you can harvest, but also, calculating from that time, you can know how much your fertilizing level and irrigation level will diminish. At 1st lev equipment(pots & seeds), your fert and irrig levels drop by 4.90% per hour. This drop rate can be seen by mousing over the rainbow colored lines that represent the fert and irrig health. At higher levels of planting equipment, the drop rate decreases so that you don't have to fertilize or irrigate your plants as often. I like to keep the fert and irrig levels as near to the optimal line as possible, within 5% over or under. </p>
Do not exceed 5% over fertilization or irrigation when you have the time. It is better to be under than over the optimal feed level line. I suspect ROM used the rainbow color scheme in the planting window to show that the bright blue and green are happy feeding level zones for a happy plant. If you strive to keep your plants feeding in those zones for the duration, you can keep your plants at 100% health. At harvest time, that maximum health will translate into 24 bundles or more of herbs, wood, or Ore sand and nuggets, instead of only 12 units at harvest.(plus, you can get bonus production potions used in all crafting and green leaf dew drops you need to gain planter ability levels.
 
Obtaining Planting Materials:
The Planting Instructor and Seed Merchant are together(In Elven Island, Logar and Veranas etc., but they are not at Reifort or Heffner Camp). Get started with a 30 minute planting quest package from a planting instructor, that comes with one 30 minute, start to finish, planting seed to complete the quest. The quest materials include one Mayan pot(1st -7th level planting pot) and more fertizer and water than you need to complete the quest. You can actually buy 4 more pots at that time, to meet your 5 pot growing level maximum number of planted pots at a time, and 50 water/50 compost from the Planting Instructor and 2 more seeds from the seed merchant. But for timing sake, you may not want to start the 30 minute seed at the same time as the others. After you complete the Planting apprentice quest, you will receive 3 more seeds, and more fertilizer and water. For a good start, plant and irrigate & fertilize to the optimal line. This will be all you need for the quest. Then come back in 30 minutes to harvest the magic fruit. The other seeds will take 24 hours to fully mature(plus 10 minutes)and they need more feed overall. You'll notice that the different seed types and pots have different optimal line feed levels. Wood seeds, properly planted, are fed to 90% at the optimal line. Herb seeds planted in the correct pots are fed at 80% at the optimal line given. The Ore seeds are fed at 70% optimally. I know that I recommended that those levels are where you always start out, to get a good healthy start for your plants. But, I have found that you can start the plants at 90% feed level for the Wood and Herb seeds planted, 80% for the Ore seeds planted. The Health of the plants may take a slight dip down to 97% because of the over feeding, but the health will come back up to 100% after the feed level is in the Blue or Green happy zone for 4 hours as the water and fertilizer are absorbed by the plants. Remembering that each unit of water or fertilizer gives 10% feed level, the 10%-20% overfeeding is gone in 4 hours and your plants are again in a nice feeding level range. This allows you to leave the game with your plants fed at 90%, and not have to return to feed them for 8-10 hours, depending on how high level your character's planting level is. After 6 hours, the feeding levels will drop by (4.90% x 6 =) {39.4% }. You can then feed your plants again with 4 units of each , irrigation and fertilizer, to bring the feed levels back up by 40%. (You see how it works, 10% feed level increase for each unit of irrigation or water) This would result in your feed level being just barely over the optimal line, but as you'll notice, the level will still be in the bright blue or bright green zone for a happy plant. At higher level planting equipment and seeds, the drop rate may go down to 4.28% (near level 19) to allow you to go longer without having to feed the plants. At higher level planting skill, 20-30th level, your loss rate may be only 4.14-4.25% per hour. Planting and feeding at 90% feed level will allow you to plant an Herb or Wood plant and leave it for 10 hours, suffering only a feeding level loss of 42.5%, only 4 unit of water or fertilizer down from where you were. You would still be in the happy green and blue zone for the Herb plant and still be 100% plant health for the Herb plant and no less than 98% plant health for the Wood plant. This small of an amount of reduced health can be made up in 2 hours of near perfect feeding level. This would easily allow you to go out of your house somewhere for a while or sleep for 9 1/2 hours without significantly hurting the health of your plants. The Ore plants are the most difficult, but not that much so. CAREFUL: Seed in wrong pot type needs 20%+ more feed, and needs to be fed more often. You don't want to work yourself to death keeping your plants healthy by having to feed them every 3-4 hours, right? Seed in correct pot only needs feed of 11 fertilizer/11 irrigation or less in 24 hours, plus the starting amount, usually 7-9 units of each: water and fertilizer. 95/95 of each irrigate/fertilize is all that is needed for 5 pots of plants, like 2 herb, 2 Wood, and 1 Ore, ideally planted.
Bonus:
At 20th level, you turn in one of the green dew drops you earned from harvesting such healthy plants for the craftman upgrading quest that allows you to continue raising your planting skill level above 20th level. You may want to keep an eye on your planting skill level so that you only plant enough to just barely achieve 20th level with your most recent planting. This way you are not shorted any planting experience from harvesting a whole bunch of plants just to go from level 19.6 Planter to 20th level Planter. But, Hey, you get to keep the harvest anyway regardless, right! At 20th level, just like a gathering level 20,(Woodcutting, Herbalism, or Mining), you need to complete the skill quest of obtaining a green leaf dewdrop, to be allowed to level your planting skill beyond level 20. But you got a dewdrop already from having such healthy plants to harvest. Just complete the dewdrop quest and then you can plant up to 10 pots at a time(The Bonus).
:At 1-7 level equipment, pots and seeds, 5-6 hours is recommended for feeding intervals, to keep the plants in the happy zone. 
:7 hours is an okay feed interval at higher level(level 13+ equipment).(~34.3% down in feeding levels - 3 units each, water/fertilizer restores 30%). 
In 8 hours, with 1-7 level seeds, pots, plant food, plant feeding levels are down by ~39.2%. 4 units of plant food(irr/fert) brings up feeding by 40%, maybe to a little over the optimal line. So , like I mentioned above, before a long break from game /feeding the plants, of 8+ hours, maybe you want to give the plants an extra unit above the optimal line, of each, irrigation and fertilizer. Overfeeding is less damaging to the health of the herb plant than the wood plant, because you have more room above the optimal line.(more bright zone) While the plant feeding level is in the bright zones, the plants are getting healthier, their health level is going up slowly, and vice versa. The longer and farther the feeding levels are from the bright zones, the less healthy the plants will become, lowering your harvest. Feeding after the plant is ready for harvest seems to have no effect on the health of the plant. You do have some bonus time after the 24 hours 10 minutes of maximum growth in order to get your harvest. (Feed at least every Ten hours or less,(plants at death‘s door maybe 60-70% health.)if you didn't compensate with extra feeding before your break) At higher levels, you can buy better water and fertilizer which allows you to go even longer between feedings. You can also mix different types of water or use different types of water to feed your plants, resulting in a hybrid feeding level drop rate of your choosing. The same with the different types of fertilizer. Higher level pots, higher level fertilizer or water, result in less need to feed as often.
If you know you won't be able to feed in 6-7 hours, then feed at 1-2 units(10%-20% feeding level) over optimal line for feeding before long break of 8+ hours. Your plant health will drop significantly into the 90's% or lower, but the plants will live.
If you must go longer between feedings, just remember:
Each hour, the feed levels for both fert and irrig drop roughly 4-5%
 
(or more precisely, the drop rate for whatever combination or plant seed, water, fertilizer, and pot you use- it varies from 4% - 5.88%)
ie. So if you must leave the plants alone for 12 hours(not recommended), mouse over the rainbow lines to see the exact feed level drop rates. If you have to leave the plants unfed for 12 or more hours often, you can't expect to keep their health at 100%, but you can still harvest live plants and reap benefits and level your planting skill. You would just level slower with more plantings needed. 
Just say you find the drop rate is 4.90% for each of irrig and fert. You know that the plant will consume 24 x 4.90% during the course of its life, one day, 24 hours. All the plant will need is 122.6% feed level of water or fertilizer(compost), plus the starting amount that brings the feed levels up to the optimal line. Since you get 10% increase in feed level for each unit of fert or irrig, you then know that the plant will only need (122.6)/10 = 12.26 units of irrigation and 12.26 units or fertilizer in 24 hours. So the lonely plants will only need half of that in 12 hours or 6.13 units of irrigation and 6.13 units of fertilizer to keep the feeding level from dropping below the optimal line. BUT and this is a big but, You don't need to keep the feeding level at precisely the optimal line all the time. The bright green and bright blue zones give you varying leeway, different for herb versus wood versus ore seed plantings. The Ore seeds do not allow you to leave the Ore plants unattended for as long as the others. This forces you to OVERFEED LESS. So if you go 12 hours between feedings, you may have a safe zone of 30% below the optimal line where the feeding level still keeps the plants happy, in the bright zones of the rainbow line. So instead of overfeeding by 6.13 units(really just 6 units-you can't feed fraction of plant food or water), just overfeed by 4 units(or clicks above the optimal line for each, irrigation or fertilizing. Your plant health will not be 100%, your harvest will be less, but they will live and you will get a harvest.
Harvesting is easy:
Feed at optimal line within 3 hours before harvest time, because in 3 hours, the feeding levels will still be good(near or in the bright zones)if you don't feed them anymore after that, before harvest. Each click of feed( Irrig. or Compost) gives 10%(~2+ hour) of food in correct pot. You get an extra 10 minutes before the plants are even ready to harvest. So if you planted at 5:33pm, you don't have to harvest until at least 5:43pm, the next day. I don't know why ROM did that, but it takes a little pressure off of you to get the harvest. Plus, I have harvested even 45 minutes later than the ready time, with seemingly no bad effects, when I had the feeding levels current or at happy levels for the harvest time. Just make sure you have room in your bag inventory to accept the harvest.
Go forth and harvest abundantly!Expect to get 12-24 bundles from each pot. You might get 48 bundles or Ingots, and a production speed potion, a green leaf dewdrop(save this) or luck potion.