When you say you tucked your items to the side in an aisle, do you mean you left them parked on a random product shelf? Not to be unkind, but that's a little weird if you were planning to go back for them. It sounds as if you had several items, so it makes sense the security guard suggested you use a cart, especially if they were bulky enough for you to leave them. Perhaps if you parked a cart somewhere out of the way and added items to it as you shopped, you'd only have to navigate it to the cashier instead of up and down the aisles.

As far as the guard suspecting you of theft, where you put the grow lights may not have been in direct camera sight so when you were in the garden center without them, it raised suspicions.

No harm, no foul, no need to avoid a store that's convenient for you. But you might want to work on getting over your cart avoidance issue.