Blend Photoshop gradients by a number of means. You can create a basic design, lovely colors but you can stretch it further with combinations and mixing of colors in countless ways to create all kinds of inspirational artworks. Use the powerful presets and combine them using blending modes but you can also use brush strokes and the brushes / mix etc as well as patterns and more.
Select the gradient tool. Also go to the layer menu and create a new layer. I always find it easier to work with layers and combinations of colors and if you are unhappy with the result of any of the combinations / mixes then you can quickly delete them. Set the type to radial or one of the other types, I must admit "radial" is generally my goto style)
Select a preset and apply to the current layer. As you are using the layers to mix the designs, you can leave the tool with a blending mode of normal and then apply it. As it is a normal blending mode, and unless the preset includes transparency, you can apply it again and again or if not just use the undo and re-apply the artwork
Go to the layer menu and new layer and then re-apply the preset or perhaps a different preset. Again, set to radial or linear etc and apply the design until you are happy. I would suggest at this point that you go to the windows menu and layers and then set the blending mode to difference or darken etc and you can then see the result of your color mixing.
For a true color mix / blend of designs, you can add more than one additional layer though as you add more and more layers you will notice that result probably gets worse as the mixing becomes quite a mess. That is the reason for the layers as you can always re-apply the preset or you can simply delete the entire layer by going to the layers panel.
You can also make even more amazing mixes with the presets by going to the layers panel and selecting a layer and then layer menu and smart objects commands and convert. Once the layers are all smart objects, you can then add effects to them such as oil paint or glass effects and more to create even more amazing designs.
You can create even more amazing mixes by adding in adjustments layers to the mix. If you have converted them to smart objects, you can select the layer and then add an adjustment via the image menu and you can then manipulate the hue / saturation or color balance adjustment via the properties panel. Another option to change the entire mix of all the blends of the preset layers is to use the layer menu and new adjustment layer and you can place the adjustment layer above all the layers so all the colors are changed or you can add the adjustment in between layers and only layers below are then modified.
If you are not using a vast range of effects or adjustments, you may like to go to the image menu and then go to the mode and RGB and 32 bits per channel and then create the mix of colors and applies of the tool with that mode. 8 bits is fine but 32 bits, can be useful for creating all kinds of stunning mixes with difference, darken, lighten etc. You will notice that some of the modes are disabled when you change to 32bit but the color range is extended and repeat combinations of the tool don't often end in a mess. Also, when you go back to 8bit, the HDR panel appears and you can further tweak the colors of the design to create even more amazing artwork such as tweaking the toning curve as well as modifying the gamma, exposure, detail, edge glow etc, you can achieve totally stunning designs.
Once you are happy with your design, you can always go to the layer menu and flatten image.