A metal trellis is an excellent choice for climbing plants and vines that will be heavy when they reach maturity. Plants such as grapevines can weigh hundreds of pounds when mature and laden with fruit. Metal trellises can support considerably more weight, but consequently also require a firmer foundation when constructed. Metal trellises require a firm footing to prevent tipping over and damaging plants, and may need to be cemented in place to ensure stability.
Metal trellises are durable and will last a long time, if properly maintained. A steel trellis, unpainted and allowed to rust, can fall victim to the elements inside of a few seasons. If a metal trellis is maintained, cleaned and repainted yearly, however, it can be expected to last for many years.
One consideration gardeners frequently forget to consider is the weight of their trellis. A metal trellis may be a wonderful addition to a patio planter or placed on a cement footing, but its considerable weight will cause it to slowly sink into the ground when used in a yard or lawn. This situation can be mitigated by placing cement pavers beneath its feet to disperse its weight.
A metal trellis has many advantages over its wooden or plastic counterparts, but is also considerably more expensive. If you are planting a climbing plant that you expect to be a permanent fixture in your yard, such as a grape vine or heirloom rose, a metal trellis may be the way to go. If, however, you are looking for a material for a trellis that will serve its purpose only for a season or for a temporary garden bed, lower cost alternatives such as wood and plastic may be preferable.