I will try to explain why you late wife did not have a big weed problem. She probably took care of her plants by cultivating and working the soil periodically and/or used mulch. Probably during the past few years the beds were not properly cared for, seeds blew in, sprouted, grew, produced more seed and and in a few years you ended up with a weed patch. I was under the impression that your myrtle was a myrtle tree like a crepe myrtle, not a ground cover of vinca minor/periwinkle.
Home Depot or any of the big box stores do not usually carry much in the way of organic products. You have to go to genuine nurseries or go online. Using acid has nothing to do with weeds. Some plants require a lower Ph, especially some types of flowers. You must know if your soil is acidic or alkaline to start with in order to know what to add or change in order for your plants to thrive. There are numerous organic ways to raise or lower the soil Ph. One of the best organic methods to lower the Ph or acidify the soil is with the use of peat moss and peat moss tea or if you aren't in a hurry you can use sulfur. Depending on where you live will determine which brands of organic products are available. Just go to a reputable nursery, make friends and ask questions. They will be gad to help
The best liquid organic fertilizer that I am familiar with is made by Medina and is called HastaGro