Japanese holly, hydrangea, and boxwood all tend to be fairly resilient plants, so something in the care after planting or site conditions might be causing them stress. Granted, each has its array of pests or diseases it can be vulnerable to, but that will be true of any plant grown. Usually, serious diseases or pests don't cause major damage until the plant is already under stress from some other cause, often something its growing conditions like soil moisture level (too wet or too dry).

Can you share a photo of the planting bed? More information about the site would also help us to make recommendations:

• Do deer visit the yard, where new plants should be as unpalatable to them as possible?
• Does the soil in that location drain well, or skew dry from a roof overhang (or competing tree roots), or skew wet from a nearby roof downspout outlet or leaky gutter?
• Do you want a mix of evergreen and deciduous options? Your prior attempt included both, but we wanted to ask.
• When the plants died in prior attempts, what symptoms did they have, and roughly when? (In other words, did all foliage turn yellow and brown fairly suddenly, or just individual branches discolor and die? Did leaves fall off while still green? Did foliage wilt and not recover? Was it spring when dieback became evident, or later in the growing season?)
• Aside from the 4-foot plant you request, what mature size (or limits on size) do you prefer, without relying on pruning to restrain growth?

Miri

Hi, 

Thanks for answering Miri's questions, it is really helpful! We can suggest some plants and arrangements, but it would also help to know the length of the porch. We are estimating about 24 feet  but it is hard to tell with the angle of the photo. 

The existing evergreens that were there, looking like a type of Dwarf Arborvitae, maybe Thuja occidentalis 'Teddy' or 'Bowling Ball' (Teddy is shorter usually). The Japanese holly could be one of the varieties that is slow growing. If there was a health issue it show dead branches or would have died by now. 

We would advise against a fruit tree for a few reasons. Fruit trees are generally more maintenance than people like to deal with so if you are seeking a lower maintenance planting, it may not be the ideal choice. Depending on the tree, most require pruning and certain chemical sprays, either organic or manufactured to maintain health and get a viable crop. There are a number of small tree options that could be used as an anchor point at the end of the porch though. 

For evergreens: We would recommend that you keep the Arborvitae that you have but it would look more refined to have a third perhaps near the front steps. It may be difficult to find one of similar size or have it catch up to the size of the existing plants. Maybe you could use a taller upright boxwood such as 'Dee Runk' or 'John Baldwin',  close to the stairs and add  2 'Grey Owl' Juniper in between each Arborvitae to add various texture to the beds. The Japanese Holly look like they are planted too close to the lattice along the bottom. You would want to leave about 18 inches of space before planting anything to help with air circulation and the overhang from the roof. So maybe you remove the holly and the Rose on the end. 

For a tree/shrub on the end: 

Hydrangea paniculalta species can handle more heat and dryer soils. There are dwarf varieties and larger sizes as well. A larger shrub on the end would be nice! You may have to guard it from deer to get it going until it is large enough to be able to withstand some browsing.

Hydrangea macrophylla species would probably prefer more morning sun and later afternoon shade in the heat of the summer. If you have an eastern facing location, they would probably do better there. 

Also a small flowering tree could be pretty there as well. 
Aronia arbutifolia Red chokeberry

Viburnum prunifolium Blackhaw viburnum

Amelanchier arboria Service berry

Perennials that have a fuzzy textured leaf, spikes, or strong scent are typically deer/rabbit resistant (albeit they may try some things): 

Nepeta Catmint species

Salvia nemerosa perennial salvia species 

Stachys Lambs ear species

Monarda Bee Balm species

Caryopteris Bluebeard species 

Lavender species

Rudbeckia Black-eyed susan species - sometimes - in heavy deer populations they can eat the flower heads off

Ornamental grass like Little Bluestem, Carex species that can handle sun, Prairie dropseed, Purple Lovegrass, dwarf species of switchgrass. 

Phlox subulata or Mossy phlox (you have some in a container it looks like)

Amsonia species

It would look nice to have the evergreens along the porch and put some perennials in front. Maybe extending the bed line out to the bottom of the steps and curving to the corner to encompass the tree. Be sure to look at the mature size of the plants and space them accordingly. 

If you have further questions about planting or bed preparation, feel free to reach out further.

Emily

Thanks, this is so helpful! One question on timing. Is it ok to plant in the next couple of weeks? Or have we missed the window for this year?

In general, you can plant any time of year the ground isn't frozen. 

You can plant now but keep in mind that if you are planning on traveling for an extended period of time this summer (a week or more) you may need to have someone come water for you. 

Depending on the size of the plants and what you decide to plant, you will probably need to check for water about once a week. You can't rely on rain to sufficiently irrigate new plants as they get established since it may not be enough to soak the entire root ball and develop deep root systems. Smaller root balls when planted may need to be watered more frequently in the heat of the summer if we haven't had enough rain, as opposed to larger shrubs. 

You can refer to these pages for guidance and care: 

Care of annuals and perennials

Watering Trees and Shrubs

Let us know if we can help further!

Emily