My husband and I travel often I heard about your service from a friend. It sounds great, but we have no pets at the moment, we fo have plants that need regular watering. Would tgat qualify for your service? I could not find a way to select a category.
Yes you can create a listing for your requirements.
We did a lovely sit in France where our only responsibility was the watering of flowers and vegetables after the sun had set.
While lots of people sit because they want the company of pets, I think you could also find plenty of applicants who would like the lesser responsibility of plants. As a green thumb with a house full of plants, I might choose a sit like that if I really liked the location.
Do you have one of these…? Make it easy “Plants For Dummies” for your sitters. 
We are currently on a ten-week house and plants sit - It’s a great sit!
Although not common you aren’t the first person to have asked this question. I would think you’ll be inundated with applicants - well 5 anyway until you decline some. Make absolutely sure though that the sitters you pick are likely to water your plants. I’m not sure how you can guarantee that other than questioning and making a judgement as to whether they have an interest in plants. There have been sitters who have let plants die through lack of watering.
Lucky you!
I think a lot of sitters would love to have a little break from pets for a little while. We sit full time, and we love pets, but having the odd little break from dog walks etc occasionally would be a lovely experience to have, and I think a lot of sitters on here would love it too.
Hope the daily feeding schedule is not to much haha
There are not many house sits without pets, but in most instances people jump onto them. If it’s not to crazy I think you could fill it very quickly.
Good luck
Yes, I look for both cat sits or plant/garden sits.
Not easy during a heatwave though.
The UK gardeners will all need to adapt. These multiple heatwaves now happening will change gardening conditions. There will be plants that no longer cope with the extremes. Watering isn’t everything, certain species won’t be able to survive. On the upside plants that have needed different conditions will be a possibility. It’s a changing world.
It’s easier than ever, if anything dies, it’snot our fault 
@LoisL, we’ve completed several housesits that did not have pets.
Couple of them were repeat sits were pets had alas passed from prior sit, but hosts still wanted us to complete housesit.
But more have been homeowners traveling overseas and simply prefer that someone live in their property. This can avoid costs to complete regular property checks for home insurance policy compliance. Or can simply let a host enjoy their trip without worry about home. All good. For example, we completed a three-month (private, not THS) sit last year without pets. And will return to same hosts later this year.
We see plant care as similar situation.