Q&A: Fruit tree considerations for the home garden

a grove of peach trees
Peach trees. Photo M. Talabac

Q: I’d like to eventually grow some of my own fruit. What’s a good starting point and what do I need to consider?

A: It’s fun to try growing your own food, though fruit trees require the greatest amount of commitment and patience to be rewarding. Ill-prepared first attempts can easily end in failure. We suggest inexperienced gardeners or anyone short on time try small-fruit (berry) cultivation first before diving into fruit trees – they’re much simpler to grow, need little to no spraying, and take up less space – but if you do enough research to know what to expect, you can certainly start small so it’s not overwhelming.

Easier crops for a novice grower to start with include fig, persimmon, and some of the more esoteric fruits like jujube, serviceberry, and pawpaw. Ironically, the most popular fruits – apple, pear, peach, plum, cherry – are the hardest to grow well in our mid-Atlantic conditions. This is not due to temperature hardiness but rather disease and pest pressures.

Plan as much as possible first: where do you have enough space and the best conditions, how will they be cared for year-round, what problems should you anticipate, and how will you process the perishable harvest? Even when grown organically, there’s a lot of intervention and preventative treatments that will typically be needed to produce a useful harvest and to keep the tree healthy. After a problem arises, curative options are few, so knowing ahead of time what to look for and when is important in avoiding plant damage or a ruined crop for that year.

“Location, location, location” applies in gardening too. Fruit-bearing plants usually require full sun (6+ hours daily in summer) and well-drained soil to perform well. A site with good air circulation reduces disease, and proper pruning and training will make harvesting easier. Choose an area where you have enough space to avoid crowding and competition between plants. Different varieties mature at different sizes, and training style will also impact how much room trees use.

Most fruit trees are propagated by grafting. That means the variety you want is joined to a rootstock of a related variety for the purposes of improving hardiness, disease resistance, and/or dwarfing the plant’s stature for ease of maintenance and harvest. Terms like semi-dwarf, dwarf, and miniature refer to the overall growth habit compared to a full-size tree, not the fruit size itself.

Check which varieties need cross-pollination to fruit well, as some will not produce fruit if planted alone. Self-fruitful groups include figs, peaches, nectarines, and apricots, plus some varieties of apple, cherry, pear, persimmon, and plum. Keep like with like when you can, because cross-compatibility may not occur; for instance, don’t rely on pollination between an Asian and a European pear, or an early-blooming apple with a late-blooming apple. Web-based suppliers sometimes provide cross-pollination charts to illustrate compatible pairings. Avoid multi-graft plants (trees with several varieties grafted onto a shared trunk) unless you’re quite experienced because they run the risk of increased maintenance headaches or the loss of an entire variety’s crop.

ripening figs on a fig tree
Fig fruits.

Good inherent disease resistance goes a long way to reducing pesticide use and lowering the risk of bad outbreaks. No varieties are immune to problems, but those with noted resistance aid your efforts tremendously. It may surprise you to learn that some of the most popular varieties found at supermarkets are not the more disease-resistant options or even easy to grow overall. Ideally, narrow your options down by resistance traits first, desired flavor and other traits second.

Our website has a lot of information about growing fruit. You can search for a specific fruit type and find information on plant selection and good care practices.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Growing and using blackcurrants

Gardeners adding fruit to their landscapes tend to think first of familiar treats such as raspberries, blueberries, and strawberries, which are all great to grow in our region, or fruit trees like apples and peaches, which present some challenges but are possible. But if you’re the typical suburban homeowner, you look at your proposed fruit orchard, and then you look at your yard, and the two don’t match up. Maybe that’s a matter of sheer space available. But often, it’s a matter of sun.

Most fruiting plants really prefer a full-sun location, which is something that those of us with mature trees lack. If your landscape trees are still small–well, someday you’ll get to the point where you have more shade than sun. Trees are wonderful and we should all plant more of them, but then we do end up without much space left for that meadow of sun-loving native perennials, never mind the vegetable garden and the orchard.

But what if I told you that you can plant fruit in the shade?

Continue reading

Introducing the king of fall fruits: persimmons!

It’s fall, the air is starting to get crisp, you are walking and you see these strange trees. You are sure that they are trees, yet they have these fruits that look like tomatoes… but they are on a tree. What are those fruits? They look so attractive with that wonderful orange… should you harvest them? Should you eat them? Are they any good? What IS this? In today’s post, I want to (re)introduce you to these plants and their fruits, and hopefully the next time you see them you will have answers to all those questions and will know what to do. 😉

persimmon tree in a yard
In the fall, persimmon trees are recognized for their many orange fruits that look like tomatoes! Photo: P. Tain.

What are these orange fruits?

These fruits are what here in the USA we call persimmons (from the Powhatan word “pichamin”). Persimmons are the fruits of a group of trees that belong to the same family as ebony, and that can be found on a number of continents, including North America. Among all the persimmon species that exist, a number of them are edible, producing fruits in late fall. In the USA, there are two persimmon species that produce edible fruits, and one of them is native to right here in Maryland: the American persimmon (Diospyros virginiana).

Although the wild American persimmon still grows in our forests and was well-known by native Americans, who used its hardwood, consumed the fruits, and introduced them to the European colonists (see some Native American legends involving persimmons here), the American persimmons we see cultivated in orchards come from selected lines. Indeed, varieties of American persimmons have been selected, and many cultivars of American persimmons can be purchased and grown in gardens and orchards to produce fruit. Besides the American persimmon, there are also other species available for purchase, in particular the Oriental persimmon (D. kaki), which is very well-known in Europe.

close-up of an orange persimmon fruit in a tree
The American persimmon tree harbors fruits that turn orange, soft, and tend to fall when they are ripe. Photo: W. Pollard.

Although American and Oriental persimmons are edible both raw and cooked (see here for some recipes), it is important to note that the fruits are very astringent prior to ripening, meaning that they have to be ripe for them to be palatable. The level of ripening is usually shown by the coloration of the fruit (ripe fruits are orange), its softness (ripe fruits become soft to the touch), and their voluntary falling from the tree while not rotten. It is often said that persimmons need to go through a frost in order to ripen. This is in fact not accurate: unripe persimmons will simply rot after a frost; ripe persimmons will not rot after a frost and will in fact start slowly drying out, which will make them become sweeter. This may have led people to assume that frosts actually lead to ripening, while the frost will not help in the ripening of any fruit that was not already ripe at the moment of the frost.

Is it true that I need to plant more than one persimmon tree to have fruits?

The short answer is mostly no. American persimmon trees are what we call dioecious plants. This means that each plant will either harbor female flowers (which will become fruits) or male flowers (which will provide pollen for pollination and will not produce fruits). The first consequence of this is that if one plants or encounters a male plant, it will be impossible to ever harvest fruits from it. The second consequence of this is that a female persimmon flower needs to receive pollen from a male plant in order to produce seeds (and reproduce). In most wild forms of American persimmons, pollination is also required for fruit production.

small yellow flowers on a persimmon tree
American persimmon trees display small and delicate white flowers, which are either female or male. Photo: M. Beziat.

That being said, female plants of most selected cultivars of American persimmons can actually produce fruit without pollination. If they do not receive any pollen, these female flowers will still develop into fruits, which will not harbor any seeds and which will be fully edible. If one were to plant these cultivars in their garden or orchard, fruit production would not be restricted by female flower pollination.

But does that mean persimmons do not need pollinators?

Not really. Wild persimmons still need pollinators to transfer pollen from the male to the female plants. So who are these pollinators? In fact, we know relatively little about wild persimmon pollination. In terms of flowering time, American persimmons flower between May and June, and their flowers are small and white (and cute!). Floral visitors have not been extensively studied, but there is at least one study describing a large variety of wild bees (e.g., sweat bees, bumblebees, leaf cutter bees) visiting their flowers. From this respect, persimmons play a role in sustaining this group of pollinators and will benefit from their pollination services.

immature and adult moths that use persimmon trees for food
Persimmons also support other insects including many lovely moths from our region, such as Luna moths – top – and Regal moths – bottom). Photo: Askalotl, C. McClarren and A. Reagol, M. Clock-Rust.

Although not pollinated by them, persimmons also support other types of insects (and sometimes pollinators): moths! In fact, persimmon leaves are the favorite food of caterpillars of many native moths. In particular, Luna moth and regal moth (besides many others) caterpillars prefer persimmon leaves. It appears then that persimmons do not just feed us with their delicious fruits, but also feed many of these beautiful native moths, allowing for them to maintain their populations in our area!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí. Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Pawpaw: America’s Fruit

Pawpaw (Asimina triloba) fruits ripening. Photo: Deana Karras

One of our most frequently asked questions in the developing orchard at the Baltimore County Master Gardeners’ Demonstration Garden may surprise you (it did us!) — “What do you know about pawpaws?” *

The pawpaw (Asimina triloba) is a small native fruiting tree found along stream banks and forest edges and often as an understory tree in moist areas. My first encounter with them was along the canal towpath in Potomac where I found 6” soft yellow fruits littered the ground. There was a short step from that discovery to growing my own.

Pawpaws produce the largest edible fruit native to the USA, with a range south to LA and GA, north to IL and PA, east to the coast, and west to Nebraska. An attractive tree with large drooping leaves, pawpaws have a pyramidal shape and generally reach 10-20’ in height (but can be controlled for size). Although in the wild they seek some shade they should be grown in full sun for best fruit production. Trees tend to sucker and form clonal colonies in shade but this can be easily controlled. Growing two or more varieties will produce a greater fruit yield. They are a temperate member of a tropical family that will grow and fruit in Zones 5-9. Ideally, pawpaw trees like a soil pH between 6 and 6.5 but will tolerate a much broader range. Consistent moisture is key as well as good drainage. Once established they are quite drought tolerant. Best of all, pawpaws require no herbicides or pesticides to thrive, having few pests or diseases.

In spring small maroon bell-shaped flowers emerge before leaves. These flowers have a mildly yeasty smell to better attract their pollinators: carrion flies, fungus gnats, beetles, and ants. The flowers have both male and female parts. The female pistils and male stamens mature at different times within the same flower, so a single flower is capable of self-pollinating. This, however, rarely allows for fruit set and two genetically different trees are necessary for solid fruit production.

Fruits form in small clusters rather like bananas and slowly mature through the summer. In Maryland, they will ripen by mid-September. When ripe, the fruit will drop to the ground (warning: many four-legged critters enjoy pawpaws once they hit the ground!). Resist the temptation to pick green fruit – if picked too early it will not ripen. The fruit is usually 2-6” in length often with a shape that resembles a small slightly irregular mango. In the wild they are usually 1/2 lb. or less but cultivated varieties can exceed 1 1/2 lbs.

Ripe pawpaw fruits. Photo: Getty Stock

Experiment a little with the fruit to see whether you prefer them just off the tree or allowed to ripen a few days (the skin will turn black) for added sweetness. The texture is creamy or like custard and the taste is often described as a cross between a banana and a mango with hints of pineapple. The skin is thin and easily removed. Try cutting one in half and scooping the pulp out with a spoon. Pawpaws have two rows of large, glossy, black seeds. Many cultivars have fewer seeds and a higher pulp to seed ratio. The fruits are highly perishable, a trait that contributes to the challenge of commercial value. 

In my yard trees seed freely. Seeds must be kept moist to germinate and do require stratification. They are tap-rooted so it is preferable to transplant them when very young. If purchasing plants, potted are preferable to bare-root as the root is fleshy and brittle and requires good care when handling. Pots should also be at least 7-9” deep to accommodate the long root. From seed to fruit is approximately 8 years.

Importantly, pawpaws are the only larval host for the beautiful zebra swallowtail (a large black and white striped butterfly). The caterpillars produce no significant damage but if you see holes in your leaves, it was most likely due to this caterpillar. Lucky you!

Pawpaws were a significant food source for Native Americans, high in potassium like bananas, with significant amounts of vitamins A and C, and high in unsaturated fats. They were collected from the wild by the early colonists. In the early 20th century cultivars began to be developed in earnest. After centuries of native crops, availability in the wild has greatly diminished and pawpaws are now more of a local specialty. Some of the best new cultivars are Peterson Pawpaws named after Eastern rivers such as Potomac, Allegheny, Rappahannock, and Shenandoah. For curated lists of cultivars see the references below. Young trees are readily available at many nurseries.

So what to do with your abundance of fruit? Anything you can make with a banana can be substituted with pawpaws. Pawpaw bread is delicious. So is pawpaw ice cream, recipe below (great with walnuts added).**
     2 cups pawpaw pulp or more
     1 cup sugar
     2 cups cream
     2 cups milk

Combine the pawpaw and sugar. Stir in the cream and milk. Pour the mixture into an ice cream maker and freeze according to the manufacturer’s directions.
(Recipe from Pawpaw: In Search of America’s Forgotten Fruit)

Resources:
PawPaw: In Search of America’s Forgotten Fruit, Andrew Moore, Chelsea Green Publishing, VT, 2015.
For the Love of Pawpaws: A Mini Manual for Growing and Caring for PawPaws – From Seed to Table, Michael Judd, author and publisher, 2019.
North American Pawpaw Growers Association, www.ohiopawpaw.com
Kentucky State University Pawpaw Program, www.pawpaw.kysu.edu

* We have two young pawpaws in the Baltimore County Demonstration Garden that blossomed just this year but did not produce fruit. Fingers crossed for next year!

** [Revised 8/3/21: Fully ripe pawpaws can be enjoyed in small amounts as a seasonal treat. Long-term consumption is not recommended.]

By Deana Karras, University of Maryland Extension Master Gardener, Baltimore County. To connect with Master Gardeners in your county, visit the Maryland Master Gardener Local Programs page.

Berries, birds, and cicadas in 2021

For me, at least, it’s been a bumper year for berries.

Black raspberries in my garden in mid-June

In some years, I harvest only sparsely from the various fruit plantings in my landscape. Black raspberries, in particular, get snatched by birds before I can get to them. Not this year. I had them all to myself until this week, and they’re now pretty much done anyway. My guess—and I haven’t seen any science to back this up, but it makes sense—is that the birds have been too busy scarfing down cicadas to bother with berries. Now that the cicadas are gone, they may turn their attention to my fruit-bearing bushes, but I’ve had a head start.

Periodical cicadas are not an unqualified blessing for fruit growers, of course. Female cicadas lay their eggs in branches of a certain diameter, which are abundant on a lot of fruiting plants. This can cause dieback at the ends of these branches. The affected branch tips will fall off naturally over time; you can prune them if they bother you, but remember that cicada eggs are inside slits in the branches, and won’t hatch until probably August. I’m just going to leave mine alone.

Below you can see dieback on blueberry and pawpaw plants caused by cicada laying.

I didn’t bother covering most of my fruit plants, but here in Germantown we didn’t have a huge number of cicadas, either, so the damage has been minimal and the plants will recover. Some growers used netting to keep the bugs out, which is of course really inconvenient if the plants fruit during the same period. I was startled a number of times while harvesting when I moved a branch and suddenly encountered staring red eyes. The cicadas found my blueberries early on, as you can see by this nymph exoskeleton still clinging to a berry that ripened underneath it.

But they are not competition for the fruit itself, and since the birds have been ignoring the berries for the most part, my freezer is full of blueberries, black raspberries, and blackcurrants. I’ve made blueberry chutney, blueberry syrup, and blueberry-lavender shrub (from this book). Shrubs are refreshing drinks made from fruit, sugar, and vinegar, ready in a week or less to be enjoyed mixed with sparkling water or in various alcoholic and nonalcoholic blends. I have plans for jam, cassis and other alcoholic infusions, baked goods, and more.

Fruit-bearing shrubs and trees fit into a home landscape very well. Raspberries and blueberries are great starter plants; I also recommend currants for a shadier spot, though you will not be eating them fresh off the plant, so add in some processing time in addition to harvesting time. (Also be sure that you buy varieties resistant to white pine blister rust, for which the currant family is a host.) Pawpaws are wonderful native trees that add dramatic flair to a landscape; you need at least two genetically-different trees for cross-pollination. They will take several years to start bearing, depending on the size of the trees you plant, and mature trees do sucker prolifically, so you will end up with a pawpaw grove that needs some maintenance to keep under control. But the fruit is not commonly available for sale commercially, and it has a great banana-mango flavor that’s unusual in our temperate climate. You can also try blackberries, gooseberries, and figs. All of these are easier to grow in our climate than tree fruits like apples, peaches, and pears, but if you like a challenge, those are possibilities as well. You can find advice on all sorts of fruit growing on the HGIC website.

I’m wondering how next year will go in my fruit-growing adventure. All these cicada-stuffed birds are laying more eggs and raising more youngsters this year, so the population will be higher in 2022, and there won’t be any periodical cicadas to fill their bellies. So I expect I’ll have to be more vigilant about protecting the plants I can protect in order to have much of a harvest. But I’ll probably still have some leftover blueberries in the freezer, and plenty of jars of jam and chutney. Every year is different in gardening, and 2021 will definitely stand out in my memory for noisy cicadas, happy birds, and plentiful berries.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Apples and strawberries, or how pollinators feed us

You may have heard that pollinators are suffering and that we need to support them so they can continue to stay around us. You may also have heard that as humans, we need pollinators because if we lose them, we also will lose our ability to feed ourselves. How is this so? In this blog post, I want to take some time to think about the importance of this, visiting two examples of foods very familiar to us: apples and strawberries. Hopefully, by the end of this article, you will be sending loving thoughts to pollinators every time you take a bite of these delicious fruits. 😊

Do apple trees need pollinators?

Like for all fruits, apples form after the fertilization of the ovules present in the apple flowers (check out this blog about how this works). If pollination and then fertilization happens, we end up with juicy and large fruits, which enclose the plant’s seeds, and which can be used by the plant to disperse their seeds. For this reason, the fruit we eat will only form if there has been fertilization. Unlike other plants which can use their own pollen to form fruits, apple flowers (but also cherries, apricots, and peaches) cannot do so, and they need to have an organism actively transfer the pollen from one flower to another: a pollinator!

Pollinators of apple trees can be of many types but they are mostly bees. These insects are sometimes managed, with a large series of honeybee or mason bee colonies brought to orchards or gardens to support pollination. Many times, however, it is not the showy presence of these large managed colonies, but the quiet “hidden” activity of a multitude of solitary and wild bees who perform the pollination of these flowers. (Read here to learn about wild bees.) These pollinators are often overlooked, but it is really these little ones that save the day in most gardens.

Apple flowers are pollinated mostly by bees, which can be managed (like honeybees), or wild (like metallic bees or native bumblebees). Photo: Hugo.

Sometimes we don’t realize the value of something until we don’t have it anymore. If you have apple trees in your garden or on your farm, you may have realized that if we have a year with a cold spell when apple trees are flowering, the tree will produce very few apples. This is most times directly related to the need for pollinators that these plants have. In fact, insect pollinators have trouble moving and flying at cold temperatures, which means that if it gets cold when the apple tree flowers, pollinators will not be able to visit the flowers because they cannot reach them. If the spell lasts throughout the whole flowering time, then most of the flowers will not receive any pollen and no fruits will be formed.

Weirdly-shaped strawberries? What’s going on?

The region where I grew up in Argentina is locally known for their delicious strawberries. Every early summer, we would get these small wooden boxes with small, sweet, and incredible strawberries. We would then wash and cut them, and eventually eat them like that or (my favorite) with whipped cream. I never thought at the time that I would today be thankful to all those pollinators for creating such fond memories I can keep forever. How so?

As most plants, strawberries can partially self-pollinate, but get better pollinated if pollinators are around. Like apples, strawberries flower early in the growing season, and a cold spell during their blooming time can make them lose their pollinators, and can lead to irregular strawberries or to no fruits at all. Why is this?

Strawberry flowers are formed by a multitude of mini female organs (shown with the black arrows, on the left), which eventually become a multitude of mini-fruits (shown with the white arrows on the right). Each of these mini-fruits carries one seed and is held by a “base tissue.” The group of all these mini-fruits and the base tissue is what we call a strawberry. Photo: A. Espíndola.

In the case of strawberries, what we consider a fruit is in fact a series of tiny fruits (each little seed we see on a strawberry is one of those fruits) all growing together and in parallel on a “base tissue.” It is this whole “mega-fruit” that we call a strawberry and that we eat. As for apples, strawberries are also particularly well-pollinated by bees, and it has been shown that it is really the wild bees that we need to thank for their services here! Also, like for apples, when pollinators are not around because they are just not able to survive in the area or because they can’t move due to low temperatures, only some of these tiny fruits will get to receive pollen and be fertilized, meaning that only those parts of the “mega-fruit” will get to develop. When this happens, we obtain strawberries that are odd-shaped and that look deformed. These strawberries can still be eaten; they are just not as full and sweet as they could have been if the pollinators had been around.

I want apples and strawberries. What can I do?

We have treated in previous blogs some specific actions you can take in your own green spaces, gardens, and orchards to help pollinators thrive and continue helping us get our own delicious food. And in fact, what better way to thank them for their help in feeding us than to provide food and nesting spaces for them!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Blueberry success is all in the soil

Farmers and gardeners learn much by daily tending soils and plants. But the winter “off-season” affords us time to dig deeper into topics of interest and learn from co-cultivators and experts in the field. I spent some time in a variety of grower meetings, conferences, and webinars in January and February where research findings were shared. Many gardeners are interested in growing blueberry so in this article I’ll share tips for success including some insights I picked up from presentations by Oregon blueberry researchers David Bryla, Ph.D. (USDA) and Bernadine Strik, Ph.D. (Oregon State U.)

Blueberry background

Highbush blueberry plants evolved to grow in low pH, high organic matter sandy soils with high water tables. These soils contain more ammonium nitrogen than nitrate nitrogen, hence blueberry’s preference for the ammonium form of plant-available nitrogen. The shallow, fibrous root system grows almost entirely in the top 12 inches of soil. Most of the roots are very fine, the width of a human hair, and can’t penetrate or thrive in clayey, compacted soils. The key to success is create garden conditions that mimic those in blueberry’s natural environment.

Blueberry thrives in well-drained, porous soils, high in organic matter (4% – 20%). The soil pH should be in the 4.5-5.5 range.

Soil preparation starts in fall

  • Begin by testing the soil in the late summer or fall prior to spring planting. For gardeners, soil testing labs provide the most accurate pH measurement of your soil, as well as baseline information on organic matter and nutrient levels. pH probes sold to gardeners are generally inaccurate and pH color kits using litmus paper are only accurate to ½ of a pH unit (5.5, 6.0, 6.5, 7.0, etc.

Add organic matter

  • The top 12 inches of soil should be one-third to one-half organic matter by volume. Peat moss (3.0-4.5 pH), plant-based compost (7.0-7.5 pH), and lightweight potting soil, a.k.a. soilless growing media (5.5-6.5 pH) are the materials most often mixed into the soil. Research has shown that adding compost (especially animal manure compost) can increase soil pH.
  • Some Oregon growers incorporate 2-3 inches of aged softwood sawdust into topsoil prior to planting. The benefit is that sawdust has a low pH, decomposes slowly, and increases organic matter levels. For Maryland gardeners, large amounts of sawdust are difficult to come by, but bark fines are readily available. You would need to apply 1.0 lb. of additional ammonium sulfate (21-0-0) per 100 sq. ft. nitrogen for the soil microbes that slowly decompose the bark fines.

Lower soil pH

  • Elemental sulfur is applied (based on soil test results) in the fall prior to spring planting, and incorporated to a 6-8 inch depth.
  • Pelletized and prilled forms of sulfur are easier to apply than powdered sulfur but take longer to lower soil pH.
  • An oxidation process, driven by special soil bacteria, converts the sulfur to sulfuric acid, releasing hydrogen ions that lower soil pH. The bacteria are most active in warm, moist soils. The process takes 6-12 months. Iron sulfate can also be used to lower soil pH but 6 times as much is required, increasing the cost.
  • Re-test soil pH to monitor pH levels and apply sulfur as needed to maintain the 4.5-5.5 range.
  • For container blueberry plants, mix 3 TBS. of sulfur into the top few inches of growing media, for a 15-gallon container, to reduce the pH by one unit (e.g. from 7.0 to 6.0).

Bag of sulfur
Elemental sulfur is available in powdered and pelleted forms

Fertilizing

  • Ammonium sulfate fertilizer is recommended because it supplies nitrogen in the ammonium form and helps acidify the soil.
  • Fertilize at full bloom and again three weeks later.
  • Urea is another good nitrogen source, recommended when soil pH is below 5.0 because it is only one-half as acidifying as ammonium sulfate. The nitrogen in urea is converted to ammonia and then to ammonium.
  • Oregon research studies show that feathermeal (12-1-0.5) and soluble fish fertilizers (4-1-5) work well in organic blueberry production. Organic growers prefer to inject fertilizers into irrigation water, known as “fertigation.” Another interesting finding was that there were no significant yield differences between the lowest (20 lbs./acre) and highest (240 lbs./acre) nitrogen fertilization rates.
  • Organic matter and organic fertilizers release ammonium ions with relatively little oxidized to the nitrate form as long as soil pH is in the 4.5-5.5 range. When soil pH is >6.0 most of the nitrogen from decomposing organic matter will be converted to the nitrate form with negative effects on plant growth.
  • Oregon research indicates that organic acids (humic and fulvic) applied in liquid form, increase blueberry root growth while lowering soil pH.

Developing blueberries
Blueberry fruits developing

Watering

  • Blueberry root systems need to be kept moist. Plants can tolerate hot weather but not drought. Water your blueberry bed thoroughly and consistently when rainfall is lacking. Soaker hoses and drip irrigation work well.
  • Blueberry grows and produces best when the pH of irrigation water is <7.0. Commercial growers often acidify irrigation water to maintain low soil pH. The pH of municipal water in our region is typically 7.5-7.8 and has a high salts and bicarbonate content. Just be aware that your irrigation water can drive up soil pH.

Blueberry plants in large fabric bags
Blueberry plants in large fabric bags

Mulching

  • Blueberry roots cannot compete very well with weeds for nutrients and water. Mulch is essential to keep soil cool, improve water infiltration, conserve soil moisture, reduce weeds, and increase organic matter.
  • Use aged wood chips (never fresh), shredded bark, pine needles, or sawdust as a mulch. These materials are low in pH (4.5-5.2) and salts, and decompose slowly.
  • Interestingly, a recommended growing system in Oregon uses strips of heavy-duty weed barrier to cover beds after they have been mulched to further reduce weed growth and moisture loss.

A well-planned and maintained blueberry bed can produce well for 20+ years. Start yours in 2021!

Resources:

Lowering Soil pH for Horticulture Crops. Purdue Extension

Organic Blueberry Research– eorganic.org

Author: Jon Traunfeld, Extension Specialist