This is a commonly asked question and I have had some immensely frustrating conversations over the years , because there is no specific answer when there is so many variables in play.
Palms, like all plants, require plenty of water to grow well. Yuccas too.
In winter during the dormant period its likely the palm wont need watering at all. A palm dies if it dries out completely. Thats unlikely in winter, but you still need to check that its got water, in cold dry northerly winds the air can be surprisingly dry so even in winter its possible palms need water occasionally in long periods without rain.
During the growing season a palm needs plentiful water. The best advice I can give is to provide excellent drainage so that surplus water drains away. Its almost impossible to overwater a palm in that situation.
The hotter and drier the weather , the more water the palm sucks out of the soil, and the more water it requires. The windier the weather the more water required. In ideal conditions the soil is able to dry out on the surface between waterings . If the palm is allowed to dry out too much the soil can become hygrophobic and repel water which is dangerous. Therefore frequent waterings are best , keeping the soil below ground moist , but allowing the surface to dry.
The more leaf surface your plants have the more water they will drink. I often get asked why leaves on Trachycarpus fortunei are turning brown, and its almost always lack of water. If a palm is lacking water, it will react by dropping the lower leaves to lower water usage. Therefore a palm with a lot of leaf surface area, especially newly planted , require a lot of water.
The simplest and safest plan, whether the plant is in a pot or in the ground is get the drainage right and dont be afraid to water well when its in growth.
Newly planted palms require much more watering , the water is coming from a small rootball , and even though the surrounding soil may be wet , the rootball will dry fast and soon become hygrophobic without water. After 2 or 3 months the roots will be penetrating the surrounding soil and the need for watering less critical but to grow well a palm still needs plentiful water. This is a common mistake for people planting palms in the ground.
Another mistake is thinking that rain will suffice , summer rain is rarely heavy enough and penetrating enough to soak the ground , light rain will do little and its not uncommon for palms to dry out during damp drizzly periods .
The bottom line is that if you want your palm to grow well, give it the water it needs.
Nigel Kembrey , Hardy Palms.