Tying Up

There are many reasons to trellis plants, and many different ways to do it.
One reason to trellis a plant is for looks, a pile of morning glories strewn across the ground isn't nearly as attractive as a teepee of trellised morning glories, or a chain link fence blooming with sweet peas.  But looks are not the primary reason to lift your plants up to a higher level.  Trellising, staking, or tying up plants lifts them off the ground; it allows them to receive better light, keeps them from taking up more garden space, keeps them away from the wet ground and out of reach of some pests.  Supporting plants also helps to keep taller plants from blowing over in the wind when they are young and keeps them growing straight and tall.
By lifting peas up onto a trellis you provide a support that keeps the leaves out of contact with moist spring soil that can lead to fungus and mold problems, you ensure that the peas will get adequate sunlight despite other low-growing plants nearby, and you keep the sweet tasty pods out of reach of slugs and other non-flying pests.  You also save a lot of space.  Peas are one crop that is well-known to need a support of some kind, and while one square foot of soil can support 8 peas plants, those same pea plants if not supported would spread out in a mass three feet by three feet.  What a waste!
So yes, providing a support of some type is essential for many plants.  Among the plants that require support are peas, pole or runner beans, indeterminate tomatoes, morning glories, grapes, sweet peas, clematis, and all vines.  While these plants really need to be supported there are many others that benefit from support as well.  Winter squashes (including pumpkins), cucumbers, melons, sunflowers (sometimes they need a little help to keep winds from blowing them down), roses, luffas, etc.  Basically anything that grows more than two feet high/long could probably use some support. 

Whiskey barrel and tomato cage with eggplant, Thai chili, lemon cucumber and Tigger melon. 7/2011

In my experience there are a few types of plant supports you should have in your garden; trellises, both strong permanent ones and lightweight temporary ones; stakes; and cages.  A trellis is some type of net stretched across an area, it can have large openings in the netting (such as the 7" squares in my pumpkin trellis) or small openings.  It generally needs to be attached to some sort of sturdy frame, like a fence, or electrical conduit, or a wood frame, or even PVC pipe.  A chain link fence makes an excellent trellis for all but the largest of fruits; it has a strong frame to it and medium-sized openings to allow the plants to twine in and around while still offering enough room for fruits to grow without being squeezed in the chain.  Peas, beans, cucumbers, and many vines and flowers are all good options to grow along a chain link fence.  Sadly, I have a solid wood fence in my garden.  I add my own trellis to this fence (plastic bird netting stapled to the wood in the corners) for peas and beans.  Pumpkin trellising required a little more strength, so after a quick trip to the hardware store I built the pumpkin trellis out of 2- 6' long electrical conduit pipes, 1- 4' long conduit pipe, 2- 2' long pieces of rebar, 2- 90 degree conduit connections, and a large holed nylon (much stronger than plastic netting) net.  I drove the rebar about halfway into the ground on either side of my planting bed, connected my electrical conduits with the 90 degree connectors in an upside down U shape, and slipped the conduit ends over the rebar tops.  Then I just tied the netting tightly around the conduit pieces and slowly trained the growing pumpkin plants up over the trellis.  It is a very strong and stable trellis, yet can easily be removed and relocated by lifting the frame up off the rebar and pulling out the rebar; it can also be broken down by turning a few screws to store in a small space over the winter.  If you plan to make a trellis like this one you can find detailed directions for it in the All New Square Foot Gardening book by Mel Bartholomew.
One of the reasons I chose to use the lightweight plastic netting for my peas and beans is that they tend to become a large tangled mass by the end of the summer and pulling that mass loose from a strong netting is a royal pain.  Instead I can just cut the plastic or tear down the whole thing.  Though I think this year I will replace that net with a biodegradable version so that I can simply toss it all into the compost pile at the end of the season.  Some people dangle lines of string down to beans; I love the idea, but my beans haven't been very cooperative about climbing them without a lot of assistance, so I prefer a net.

Stakes: Stakes come in different materials, lengths, and diameters; for most plants that need staking you will want a stake no smaller in diameter than your index finger.  You can buy bamboo, wood or plastic stakes; I tried all of them and was surprised that I preferred the plastic ones. Bamboo was too flexible and the plant weight bent them, wood rotted too fast. You can also create your own stakes from things you have around the house, sticks, dowels, PVC pipe, rebar, anything you can tie a plant to.  You should select stakes about 4 to 6 feet long. Stakes are very useful supports for taller plants on which the stems are a little weak at first, or that produce large fruits that may weigh them down.  I stake young tomatoes, peppers, sunflowers and a few other things.  In my area we do get high winds late into the spring at times and staking these new transplants keeps them from being blown over.  Once tomato fruiting begins I tie all of the side branches to the stake as well as the center stalk so that large fruits won't break the branches, and to keep branches from drooping down to the ground or over nearby plants.

Cages, generally called tomato cages, are perfect for trellising cucumbers and other curcubits.  They are generally made of metal or sometimes plastic, while the metal ones will rust over time I prefer them to the plastic ones; I also prefer the square cages that can break down for storage over the round cone-like ones.  Cages will work for tomatoes, but when plants get large it often becomes difficult to find and pick fruits that are deep inside the cage.  Cucumbers tend to vine and will happily grow around the outside of a cage, leaving all of the fruits out where they are easy to reach.  This is a great way to grow cucumbers or melons in a small space like a pot.  My whiskey barrels were nearly invisible under their cuke covered cages last year.  Each barrel had a cage stuck in the center of it, and a cucumber, Tigger melon, pepper, and eggplant planted around the outside of the cage.  I tied the eggplant and pepper to the bottom rung to act as a stake, then wove the cucumber and melon vines around the cage.  Those were the healthiest, best fruiting, largest cucumber plants I've ever grown. I will definitely do the same again this year.  One of the biggest issues for cukes in my region is powdery mildew, the fleshy leaves are very susceptible and once it starts it is difficult to stop the spread of the disease.  By wrapping a cucumber around a cage or over a trellis, you keep the leaves and fruits up away from the ground and the moisture left behind by watering, protecting it from powdery mildew.  In addition, I saw a much better pollination rate in my caged cucumbers; the flowers were held up high in plain sight for pollinators and for the wind to spread the pollen as well.

Cucumber in whiskey barrel 7/2011

In conclusion... tie your plants up!!  If tying up a plant is an option, it's probably a good one.  If I had my way I'd develop a vining lettuce that I could trellis up out of the slugs' reach, but for now I'll just keep crying over chewed lettuces.