Plant cells actively control what enters and leaves the cell, so yes they do practise homeostasis. 

Examples of how the plants as a multicellular organism practise homeostasis are less obvious than in animals. This is a consequence of how their bodies are arranged. Plant bodies are arranged as a series of components. A typical animal body has component parts, but they are more reliant on each than the component parts in a plant. We have one head, one heart and two lungs, they work very well together but rearranging them into a different arrangement would end in disaster. This is not the case with plants. 

A typical flowering plant has only four basic organ types, flowers, leaves, stems and roots. Plant organs are typically more self reliant than typical animal organs and there’s rarely a fixed number or ratio of them. They’re added wherever and whenever they’re needed by each part of the plant.  This anarchic arrangement in plants is a direct consequence of their lack of mobility. A typical animal will move around hunting for food and the entire body will experience the same changing set of conditions at the same time. Adjustments to the circulating blood allow all organs to experience the adjustment. This is not the case with plants. Plants can find themselves in a range of conditions at the same time. Some leaves will be in the sun while others are in the shade, some roots will be in moist nutrient rich soil, others will be in dry nutrient poor conditions. 

The plant can be thought of as a collection of connected units. If one part of the plant experiences good conditions it will thrive, a different part of the same plant in poor conditions might die - but its death will not harm the rest of the plant.

Animals are mobile, plants are stationary - plants do use homeostasis, but not in the same way or to the same extent as animals. To a large extent, each area of the plant will thrive or die without affecting the rest of the plant. There's no re-circulation within the plant body to cause or cure a problem.