They are open from 1pm to 5pm.
Lilyvale is one, and taking the twists and turns along the narrow paths of this intimate plantsman’s garden is rewarding with a large collection of unusual hardy perennials, alpines and mature shrubs, said a spokesman for the scheme.
There is a woodland area with rhododendrons and azaleas, a young fruit orchard and a vegetable garden to explore.
Curling Pond House is the other, and its garden is dominated by a large stream-fed pond with resident moorhens.
Its banks are planted with colourful late spring flowers, and primula species abound.
The garden features the former Shieldhill Castle curling rink, a pergola walk, specimen trees and shrubs and a sweeping perennial border.
To get there, from the main Lanark to Biggar Road turn into Thankerton at the Tinto tearoom junction, where yellow signs will direct you to the gardens at either end of the village.
There will be teas served at Curling Pond House, and Lilyvale will host a plant sale.
A moth survey is being carried out too.
The two charities to benefit are Prostate Cancer UK and Dumfriesshire and Cumbria Greyhound Rescue, with the remainder going to the garden scheme’s beneficiaries.