text height and text depth specify the vertical dimensions of the text you give explicitly. As a result TikZ thinks the node's text has exactly that height and draws its box like that.
You can use minimum height to set a minimum vertical size of the node, and minimum width for the width (while text width inserts line wrapping at the specified width minimum width does not). The result will be a box in which your text is centred, but the box must have at least those dimensions. Note that minimum height is both height and depth around your text (evenly). If you want line wrapping text which is horizontally centred you can use text width and text centered.
Compare the following:
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[node distance=2cm]
\node(1)[text centered,text width = 0.25\textwidth, minimum height = 3 cm, draw]
{title is very long and long};
\node(2)[minimum width = 0.25\textwidth, minimum height = 3 cm,
draw,below of=1,anchor=north]{title is very long and long};
\node(3)[text centered,text width = 0.25\textwidth, text height = 3 cm,
draw,below of=2,anchor=north]{title is very long and long};
\node(4)[text centered,text width = 0.25\textwidth, text depth = 3 cm,
draw,below of=3,anchor=north]{title is very long and long};
\node(5)[text centered,text width = 0.25\textwidth, text depth = 1.5 cm, text
height = 1.5cm, draw,below of=4,anchor=north]{title is very long and long};
\end{tikzpicture}
\end{document}
text heightspecifies the height of the text, so adds space above the text. You could usetext depthto specify a certain depth, which adds space below your text. But I guess you don't want that, either. You're most likely looking forminimum sizeinstead oftext height.text depth? See my updated question. – Viestursminimum sizeorminimum height, the latter if it's just about vertical dimensions (you already specified horizontal dimensions withtext width).