Mr. Gardener's lovely garden

Hi, I am Lucas McDonald , also known as 'Mr.Gardener''. I am 30 years now, I am going to tell you what happened after my 12th birthday

 My grandfather had gifted me 3 sunflower plants as a gift. He was the one who got me the interest in gardening. I watered them every day at 12:30 in the afternoon. But after just 5 days unfortunately, my grand father died. He left a code message hinting about something he left me, it said;

IOGHIOVBERYUOPUIM,YUM,ASNMGHOPTYRTERERSDOPM,WEHJERRTERIONMTYHJERGHASRTDFERNM

I didn't understand it, nor did my parents. I decided I was gonna investigate. I started off by trying to flip the paper, of course it made no sense. I tried the letter before the letter, I -> H it didn't work, I decided to upload this image on google to see, I didn't get a result.

I noticed something after a few hours, I had to read the alternate letter starting from the first!

IOGHIOVBE  It said I give!

I coded the same for others and got the message " I GIVE YOU MY MANGO TREE,SOMEWHERE IN THE GARDEN."

I went to the garden, I didn't see anything indicating to a mango tree, I searched all around the garden and saw the sunflowers, I looked under one of them, there was a hole dug, with a big mango seed in it. 

I look out of the window and see my daughters and our cat relaxing under the tree, I thought I saw a white mist that looked like my grandfather, smiling.