I think offering service packages are fine as long as you know what that package is going to cost you. $10 extra per week maybe to weed the beds of a smaller landscaped property may make you extra money as once you get them out they wont grow back as fierce and may only take you 2 minutes to do. Weed control and fert cost you money, how much does it cost you to do this service? Aeration, how much does it cost you to do that service? Tree and bush trimming, etc.... Some of the bigger players on this site offer different package levels for what some of their customers may need. But I know they are thoroughly thought out and the prices they list on their websites are the "starting" prices. I think most give a discount on a bundle when they sign up for auto pay on a credit card and pay either the 1st or 15th of the month rather than at the end of the month.
If it was me I'd figure out what each service would cost individually, add the costs up, then make a bundle with that cost as a flat monthly fee. And offer a discount for paying with a credit card on the 1st or 15th of that service month. For me I need something out of the deal if I'm giving one. This is probably where a good contract can come into play. Big jobs like first clean ups that include trimming, edging, mulch, etc.. would have to be priced separately but the maintenance on that could be a weekly/monthly charge. You wouldn't want to put a large job in a spread out payment because if someone walks you've eaten a big loss. I've thought about this kind of service too and still need to think more about it. I'm not a licensed applicator so those services are out (for now) but I like the idea of up-selling more services to take care of maintenance needs but a consistent monthly bill for them and myself. Small tasks that could bring in more money that they may never have thought of. Just gotta be a good salesmen to show the benefits of them parting with more money. Like showing them that priced individually it will cost you $XXX.XX but bundled and paid by the first of the month on your credit card will cost $XXX.XX saving you $XX.XX. Also you have to find the right customer for this.
I think the idea is right, you just need to really sit and think about how to price it and sell it. If you add too little you'll get disgruntled and it may show up in your service because you're upset. You may even find that pricing individually is better.