For large altar sprays (standing or in a container) florists usually begin by greening the arrangement in with a large palm leaf of some kind.
For this tutorial, I've used Jade palm. Other varieties that work well are TeePee or Emerald. Some online flower wholesalers insist you buy at least greenery and flowers 10 bunches at a time. That is a lot of greenery. Averaging $14 or more per bunch is ridiculously high. Greenery is usually the cheapest part of a floral design! I sell Jade for about $7 - $8 per bunch . . . and I'm charging RETAIL!
I offer both fresh flowers and greenery in single bunches, allowing each of my customers to mix and match flower varieties and greenery. I may not offer "free shipping" . . . but trust me - they've certainly got that built into the price!
Use my Flower Calculator to find out exactly how many bunches of each flower you need. You may find you'll spend the same amount of money and get a mixture of flowers and greenery more suited to your desires.
Remember this is a fresh product. Not every leaf is going to be perfect. If the jade has brown tips, florists usually trim the edges of the leaves before inserting into the design.
Once the leaf has been trimmed with scissors, I insert the first palm into the side of the arrangement. Now you can see why the foam needs to be raised above the rim of the container.
Without that extra couple inches of foam, your greenery and flowers will look like every stem is sticking straight up. You want the final arrangement to be attractive from at least a 3/4 view including the sides.
The greenery is going to be the framework of your design, establishing how large the final arrangement will be. Typically the flower heads will extend just a bit beyond the longest greens.
Now in insert a trimmed palm directly out the back of the design, pointing slightly upward. Whether or not you completely finish the back with flowers depends on how the floral is viewed. I typically finish off the back with mixed greenery, but place all the flowers so the are seen from the sides and front of the arrangement.
I now insert a jade leaf inbetween the back palm and the right side palm. You'll notice that the leaves are angled towards the center.
The idea is to mimic the look of a real palm plant, where the leaves stems are inserted close to the center and work their way out and upward.
Now I place a matching palm on the left side. If necessary, you may have to strip off some of the bottom leaves to have a bare stem that inserts into the foam more easily.