Found out this one just this morning. . .

Before trying this fill your inventory with lots of pots ethers and potions also blood of revival

Some guides says that in newgame+ you can unlock Lyphia and Evelyn in Chapter 3 but, i advice to do it later

I unlocked started to unlock them at chapter 8 where my chars are powered up and may mains have ful's mil and tears

In the event of the "Sealed Darkness" in Yusof River Bed there are clones around the source of the distortion these Hell Envoys drop out growth stones like diana stones and stuff my favorite is the mars stone found at the lower left dropped by the red hell envoy.

Kill every other hell envoy in the map and take out all the other monster.

the only way to kill these hell envoys is by dealing the final blow with Lyphia and Evelyn's Combination attacks
If you kill them by other means they resurrect so that means repeated drops of mars stones. so kill all other hell envoys aside from the bottom left.

I set up my 4 main chars with one hit combo skill set and level high enough to deal serious damage and postion them in the around the lower left area near the spawn point of the "RED" hell envoy
Skill sets
Wilfred: Adventurer, double action, Flash Step, Battle Order wp: Fairy Hammer acc: Ful's mil
Yuela: Double Action, Soul Shield III, Prevail III, Flurry III wp: Crescent Moon acc: Ful's tears
Emelita: Double Action, Prevail III, Magic Resist III, Sonic Scream wp: Mifuscale Staff acc: Ful's mil
Servalwi: Double Action, Prevail III, Undress III, Enhanced Barrage wp: Herse Parfaite acc: Ful's mil

Level is 70+ ea but due to the grinding in that area leveled them past 80 lolz

I lowered yuela, emelita's and servalwi's life low enough to deal 400 damage+ each turn for them but due to double action i get to use them 2 times per turn every round i get 18 mars stones haha!!! this mission have an alocated 60 turn limit after i stopped grinding til the 55th turn i got 837 mars stones due to some missed attacks but where can you find 800+ mars stones in one map???

try this and rak up on damage

Servalwi: Prevail III + Undress III + 30hp left = 390 Crit how about i spam all 837mars stones on her???

nope my wilfred currently have 125str and my yuela got 111 haven't used the mars stones yet with weapons on but i'll see if i removed the weapons and spam the mars stones

removed my weapons and it go past 100 str

there's a limit to how many mars stones you can use but i can still make use of the others by powering up my other chars

Limit on hp is as far as I know 500 (didn't check whether you can get more with eq), limit on SP/FS is 100 and you can't go past it with eq bonus. Limit on other stats (other than hit and evade, which limit I don't get how really works) is 100, though you can get past it with exp.
Sealed Darkness is indeed nice farming place for Diana/Phoebus/Mars/Vulcan Stones, but let me inform you that later in game you will get Yard Furnitures that produce every growth stone.

ok but for now maximizing sealed darkness is really awesome if you want hard hitting tough chars hope there's a monster who drops minerva, neptune, venus and mercury specially mercury

Well, in my opinion Foutain of Youth is better, because every growth stone furniture takes 2x2 place, so you can have only two of them installed at one time (that means only two types of stones will be produced at one time). What's more, stone production is rather long: HP - 12 days, SP/FP - 8, Str - 12 days, Con/Res - 18 days, Int - 10 days, Spd/Luk - 25 days (there may be some mistakes).

One more question.

If you level a stat to max (100), will the growth items have an effect afterwards?

also other way around, if you use growth items to max stat, will leveling have an effect afterwards?

Nope, you can't get past max base stat. The only mean by which you can get past 100 is equipment.
So it's not good idea to use growth stones before 99 lvl, at least not to max stat.
And if you're afraid that you will pointlessly loose stones by using them on stat-maxed char, then fear not, there is a game massage that you can't rise stat anymore, and stone can't be used (it doesn't disappear).
Another thing is, if by changing classes your stat would exceed 100, then bonus is lowered to amount which suffice for maxing that stat. For example: normaly gets +5 to each stat on last class change, but as you can see on screenshot the amount is reduced.

What I meant is quite simple. Why would you max stat with stones if you have like 20 lvls to go ? You could very well get that 20 stats through leveling.

hmmm ok gonna save up my stones for my max lvl up but it's really awesome if you want your chars to have high damage at an early stage. . . .

I changed my mind i need to use the stones on aht and other chars i set aside to level them up on highlevel maps