Normally you'd simply create a view for that. At best a block. And then place that block in the region you wanna have the Flowers printed. With a view you are much more flexible later on.

But to do it without a view you first have to pass all Flower nodes to the template. So in your `MYTHEME.theme` put:

    /**
     * Implements template_preprocess_page().
     */
    function MYTHEME_preprocess_page(&$variables) {
      
      // Get all Flower node IDs.
      $nids = \Drupal::entityQuery('node')
        ->condition('type', 'flower')
        ->execute();
    
      // Load all Flower nodes.
      $nodes = \Drupal\node\Entity\Node::loadMultiple($nids);
    
      // Pass them to page.html.twig.
      $variables['flowers'] = $nodes;
    }

Then in your `page.html.twig` do:

    {% for flower in flowers %}
      {{ flower.title.value }}
      {{ flower.field_color.value }}
    {% endfor %}