Citrus, olives, and bananas in Philadelphia?!

Sounds pretty wild, yet this is something the Philadelphia Orchard Project is experimenting with as part of a project to understand the possibilities for high tunnel fruit production in our city and region.  In 2023, POP constructed two high tunnels at our headquarters at The Woodlands in West Philadelphia.  A high tunnel is an unheated hoophouse/greenhouse structure, using only the sun’s energy to keep plants warmer.  One of our high tunnels is used for overwintering tender potted plants for our nursery, as well as for herb drying and educational space during the growing season.  

The purpose of the second high tunnel is to experiment with growing a zone 8 food forest and explore new fruits and other plants from a slightly warmer climate.  Philadelphia is currently listed as climate zone 7B (with an average lowest winter temperature of around 5 to 10 degrees F), thus we are trying plants from one zone further south (adapted to lows around 10 to 20 degrees F).  Part of this project is preparing for continuing climate change, helping to understand how to grow plants that we expect will soon be viable outdoors in Philadelphia.  The USDA recently updated our climate zone from 7A to 7B in 2023 and from 6B to 7A in 2012.  This new plant knowledge can then be shared with our community orchard partners across the city to expand the plant palette.  Even before the climate changes, many of our urban farm partners already have existing high tunnel structures that could be used for these perennial crops in addition to the annual crops they already grow.  These plants from different bioregions may also allow POP and our partners to connect to the cultures and cuisines of new communities, giving immigrants and others a taste of home with food grown in their own neighborhoods.  

This exciting project, connecting as it does to climate change, food, and culture, has received more media attention than anything POP had done in 18 years!  Check out some of the coverage by WHYY, the Inquirer, GRID, BBC, etc. 

So what are we growing and what have we learned so far? 

Zone 8 High Tunnel Plants: 

Banana!  This is the plant that gets the most attention, with bananas being such a staple food beloved in many cultures, and associated with tropical rather than temperate climates.  However, there are some hardier fruiting varieties that have been successfully grown in zone 8 and even zone 7 with winter protection.  We planted a ‘Dwarf Orinoco’, a variety from the uplands of Venezuela known for its hardiness and shorter height, in the high tunnel in 2024.  After our harsh winter, it died back to the ground, but the roots survived and it re-emerged in May and grew to an impressive size by the end of summer.  In order to actually produce fruit, we will need to get the aboveground stem to survive, which we aim to do with additional winter insulation and hopefully a milder winter.  

Hardy Citrus!  We have planted some of the hardiest known types of true citrus, including kumquats, yuzu, and citrumelo.  All three experienced some dieback last winter, but bounced back strong this year.  We harvested a few kumquats in 2024 and this year our first yuzu fruit.  Hopefully we’ll have a milder winter and more production next year.  

Olive!  We planted an Arbequina olive, a Spanish variety known for being self-pollinating, compact, and quick to produce.  Last year our tree died back to its base, but regrew over the course of the year.  It had a few fruit in 2024, but did not produce in 2025.  

Loquat!  We planted a self fertile Golden Nugget variety.  Loquat trees are hardy to zone 7 and below, but they have the unusual habit of flowering in the fall, fruiting over the winter, and ripening in the spring, which isn’t possible outdoors in our climate.  We are hoping the protection of the high tunnel will enable this.  Our loquat flowered in 2024 but did not bear fruit.  We aren’t sure if this was due to the cold or because of a lack of active pollinators, thus we might try hand-pollination when it blooms this year.  

Pineapple Guava!  This hardier guava relative, also known as Feijoia, came through the winter the best of any zone 8 plants, with no winter dieback at all.  We planted ‘Unique’, a variety known for its self-fertility and small but tasty fruit.  It flowered in spring 2025, but did not bear fruit; we’ll try hand-pollination next year.  Because it demonstrated so much cold-hardiness, we also decided to plant one outdoors in the orchard to see how it would fare.  

Korean Tea!  One of the hardiest strains of tea camellia, the plants from which black, green, and white tea are produced.  Our tea plant showed minor winter dieback, but overall hasn’t thrived or grown significantly in the high tunnel.  We also have one outdoors in the orchard that survived with row cover wrapping.  

Caper berries! Caper plants are low-growing groundcovers with the edible ‘berries’ actually being the flower buds. Planted in spring 2025, our plant was budding and flowering from summer through fall.

Chilean Guava?  Also known as Murta, this hardy guava relative has not performed well in the high tunnel.  After two plantings failed, we have now given up on this, as we suspect it may have to do with soil preferences rather than temperature.  One we planted outdoors in the orchard has now survived two winters with row fabric for protection, although it has experienced some dieback and hasn’t grown significantly in size or successfully flowered yet.  

Zone 8 herbaceous plants.  This year we also grew turmeric, 3 species of ginger, lemongrass, sea onion, and zaatar oregano.  We also planted significant amounts of rosemary, which can be iffy outdoors in Philadelphia’s climate.  All performed well and we plan to continue to diversify the understory plantings in the high tunnel. 

Other plants.  In addition to experimenting with zone 8 plants, we have planted some more temperate species to extend the season and see how they perform in high tunnel conditions.  Our ‘Violette de Bordeaux’ fig, chosen for its compact habit, experienced some winter dieback but rebounded to an impressive size and has now extended our fig season by ripening fruit into November.  Pomegranates have proven fully cold hardy outdoors in zone 7 in Philadelphia, but we wanted to see if they are more productive in the high tunnel. Our ‘Parfianka’ pomegranate produced its first fruit in 2025.  

Berries. Again exploring an expanded season of production, our high tunnel strawberries produced a good crop starting in April, a month before is possible with plants grown outdoors in Philadelphia.  We also planted dwarf blueberries and dwarf blackberries this year with expectations of an earlier crop next year.  

Annual crops.  We grew honeynut squash, with just a few plants covering much of the available understory space in one half of the high tunnel, where they were protected from groundhogs and other pests that have been an issue outdoors.  The squash vines thrived and produced a bumper crop of 161 pounds distributed to our emergency food service partners.  We also had some bonus production of daikon radishes, which reseeded themselves from a fall cover crop we had used to help break up the heavy clay subsoil. 

Honeynut squash covered much of the zone 8 high tunnel understory and produced 161 pounds of squash for distribution! (Photo: POP)

Soil Conditions

Now that soil was mentioned, we noticed when the drip irrigation system ran it would puddle up inside the high tunnel. The heavy clay soil, with other factors like the presence of mowing and construction equipment created a “hard pan”, which is a compacted layer of soil that water and roots find it challenging to penetrate. Our first step in trying to break up the hard pan was growing cover crops of daikon radish and fava beans.  

We noticed as well that water retention was low, so with the help of woodchips we mulched the surface. Woodchips don’t immediately address the whole problem so we’ve also been incorporating compost and organic matter from the PLOW orchard. Alongside biochar and compost, we also apply our brewed compost teas to increase the soil bioactivity.

Clearly the pattern and approach is to add organic matter, microorganisms, and maintain adequate levels of moisture. Overall this year was great with plants showing signs of progress, even during dry spells the plants were comfortable. Next season the POP team will experiment with making plant juice fertilizers from the wild plants around us and extracting microorganisms from the larger system of the Woodlands cemetery. It’s always helpful to remember that as we build a system above, we also build a system below.

We look forward to reporting on new successes and challenges of our zone 8 food forest in years to come!

This POP Blog was written by Phil Forsyth and Alkebu-Lan Marcus.

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