For cavity-nesting bees, you could try drilling holes into an old fencepost or standing piece of timber. It is best to give a range of different sizes, between 2 to 10 mm, and have them facing different directions.
Any type of cavity is likely to prove attractive to solitary bees. You could try using an old baked bean can: melt some candle wax in the bottom then stuff it full of old, dry, hollow plant stems, bamboo canes and even drinking straws. Hang the can up somewhere sunny and sheltered and make sure the stems/straws are pointing slightly down, so that water doesn’t collect inside them.
Many solitary bees nest in the ground. They need loose, crumbly and exposed soil or sandy banks. So, try to leave patches of bare earth in places that catch the sunshine. If you have sandy banks these are great! Just leave them undisturbed, or even try starting a few inviting holes by poking a pencil into the bank.
Although artificial homes are a great help to nesting solitary bees, nothing beats good natural habitat. A home on its own is not enough to attract solitary bees - they also need plenty of nectar-rich flowers close by to feed on. The best gardens for bees will provide a good year-round source of nectar and pollen, from spring bulbs and pussy willow in March, to ivy and asters that flower later in the year.