Fruits

Blueberry success is all in the soil

Maryland Grows4 Comments

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

Pawpaws: The tropical fruit from our forests

Maryland Grows7 Comments

Spring is almost here and now we can start thinking about trees to plant if we did not get to that in the fall. Thinking about trees for my garden, I came back to one I have been considering for a while now — one that gives delicious fruit, is native, makes me think of tropical lands, and is not liked by deer! Today’s post is going to be about a little-known tree that’s native to our region, and whose fruits were apparently one of George Washington’s favorites: pawpaws!

What are pawpaws?

Pawpaws are trees that belong to the same plant family as chirimoyas and custard apples (Annonaceae, the soursoup family; Figure 1). From a botanical perspective, pawpaws are really special because they are the only member of their family adapted to growing outside of the tropics and able to survive our temperate climate.

pawpaw and related fruits
Figure 1 – Pawpaws (left), chirimoyas (top right) and custard apples (bottom right) are all in the same plant family, but pawpaws are the only group adapted to growing in temperate climates.

All pawpaws grow in southeastern North America, but the most common and widespread species is the common pawpaw, Asimina triloba, which is very abundant in our region. The common pawpaw is adapted to growing in well-drained and fertile habitats, such as those found in our forests. I promise you that if you ever walked in a forest in the area, you have seen hundreds of pawpaws growing in groves (Figure 2).

Pawpaw grove
Figure 2 – Pawpaws grow in well-drained fertile soils, and are common in our forests where they often grow in groves. Photo: Katja Schulz.

Why are pawpaws such a “thing”?

Besides being great native trees that grow well in our region, pawpaws have the most delicious fruits. They are considered the largest edible fruits indigenous to the continental United States. The fruits look a bit like a green mango from the outside, but are white/yellow and fleshy in the inside (Figure 3).

pawpaw fruit
Figure 3 – Pawpaw fruits are green on the outside and white and fleshy on the inside. Note the very large seeds. Photo: Elizabeth.

Their flavor is such a delicious one that I always relate it to tropical fruits. People more technical than I am in terms of flavor description say that it is a custard flavor, close to that of bananas, pineapples, and mangos. In any case, believe me when I tell you that these fruits are absolutely delightful and can be eaten fresh, in yogurts, in cakes, as jams, or frozen in ice cream!

Why didn’t I know about this before?

That was my very question the first time I tried them! It turns out that producing pawpaws for selling is not super simple. In fact, the fruits are fragile and thus can’t be transported long distances, which reduces their marketability. This means that pawpaws are usually produced and consumed locally. If you do not happen to know somebody with some trees on their land, you probably never got to try them.

Also, the pawpaw fruit season is relatively short (end of the summer), which means that one has to be in the right place at the right time to eat them. In season, pawpaws can be purchased at local farmers’ markets or on farms. You can also try to find them in the forests of the area, where you will be able to smell the sweet aroma of the fruits while you hike or bike. However, be sure to check property rules; harvesting plant materials from park lands is typically prohibited.

Why are you talking about this now? It’s not pawpaw season yet!

That is correct. However, it is pawpaw planting season now, and soon will be pawpaw pollination season, both needed to actually get the delicious fruits in the summer. So, how to plant and pollinate them?

Pawpaws can be grown from seed, but the simplest way to get one for your land is from a nursery. Several nurseries in the area sell pawpaw trees, and your best choices are those which grow trees that are adapted to your local conditions.

Pawpaws are not hard to grow and can be actually cultivated in your own back or front yard! Further, some counties and cities provide financial support to plant these native trees (see for example, Chesapeake Bay Trust and the Maryland Department of Natural Resources).

Pawpaw trees start producing fruit a couple years after planting. However, fruit production is a bit different from that of other fruits you may be growing. In fact, fruits will form only if there is cross-pollination (see this other post), since a pawpaw is not able to properly self-pollinate. This means that pawpaws need pollinators to produce fruit.

pawpaw flower
Figure 4 – Pawpaw flowers have evolved to attract and trick flies and beetles by looking dark and smelling like ripe fruits, the insects’ preferred food and egg-laying site. With this trick, the plant cross-pollinates their flowers without offering any reward to the pollinators. Photo: Judy Gallagher

Pawpaws are pollinated by flies and sometimes beetles, which the flowers attract with their maroon flowers and their ‘yeasty’ aromas (Figure 4). These scents are known to ‘trick’ the pollinators into visiting the flowers, mimicking the odor of ripe fruits that these insects prefer to feed on or lay their eggs. Flowers then attract these pollen dispersers, who, while visiting the flowers, will cross-pollinate them without their will.

You can imagine by now that having more than one pawpaw on your land or in the surroundings of your house will increase fruit production. It will then be more likely that the fooled pollinators will have visited another plant and thus carry pollen when they visit your tree.

Alternatively, if you would like to be absolutely sure to get a good pawpaw crop, you can cross-pollinate them by hand. To do that, get a small brush, pick pollen from the anthers of one flower (check the drawing here to find them), and transfer it to the stigma of another. That way you will get to live your best pollinator life! 😊

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

Gardening resolutions 2020

Maryland GrowsLeave a comment

Happy New Year! At the beginning of January we typically think through what we plan to do better in the coming twelve months in all aspects of our lives, whether that’s reading more books or committing to a fitness program or eating healthy. Of course we don’t always follow through, but it’s still worth considering what might make our lives better–including our gardening lives! Here’s just a snippet of what I’m focusing on in 2020. Continue reading →

Winterizing figs and planting cover crops in a changing climate

Maryland Grows1 Comment

Planning, preparation, timing, and flexibility are becoming more important for food gardeners trying to adapt to climate change. For example, some gardeners are planting more late crops and reaping larger and longer harvests of leafy greens in the fall. But severe cold snaps can punctuate long periods of mild weather and injure plants, so being prepared to cover and protect those crops with a floating row cover is still essential.

Similarly, HGIC receives questions each year from gardeners about protecting figs from cold winter weather. If climate change is giving us milder winters do we still need to protect fig plants over the winter? The answer is yes, for most Maryland gardeners, because severe cold snaps will kill aboveground wood even if the average winter temperature is rising. Bending stems as close to horizontal as possible and covering the plant with a tarp or other insulating material is a time-honored technique:

Photo of cinder blocks weighing down fig stems
Two cinder blocks used to weigh down supple one and two year old fig stems. The stems could have been pruned to a more manageable length. Photo credit: Jon Traunfeld

 

Photo of Bags of leaves around Fig Plant
Fig plant is completely surrounded by bags of insulating leaves.
Photo credit: Jon Traunfeld

Planting cover crops in late summer/early fall is a great way to improve and protect soils. Some vegetable gardeners had tomato, pepper, cucumber and other crops going strong into October and asked us if they could plant cover crop seed past the recommended end date of October 1st. Mild conditions and sufficiently high soil and air temperatures allowed for successful late planting well into October. But if you don’t carefully monitor the 7-10 forecasts you can end up wasting time and money.

This cover crop was sown on November 3rd in Central MD and included winter rye, crimson clover, and hairy vetch. The temperature cooled considerably from the previous week, dropping to a record low of 25⁰ on Nov. 9th:

Photo of soil and seeds
A few hairy vetch sprouts are visible but may be killed by freezing temperatures. It’s unlikely that the crimson clover and annual rye seeds will germinate and survive.
Photo credit: Jon Traunfeld

 

The availability of tree leaves in fall gives gardeners some flexibility and another option for soil improvement. Leaves can be spread out over the soil to prevent erosion, improve soil health, and provide a nice mulch for next year’s garden plants. Climate change is forcing us to be better planners and to act quickly when dealing with extreme and unstable weather.

Photo of bags of leaves
Tree leaves are valuable for soil and plant health. Don’t let them leave the neighborhood!
Photo credit: Jon Traunfeld

More fig and cover crop information:

https://extension.umd.edu/resource/growing-figs-maryland
https://extension.umd.edu/hgic/topics/cover-crops-protect-and-improve-your-soil

By Jon Traunfeld, Extension Specialist

Like Figs? Thank a Wasp!

Maryland Grows7 Comments

Last month I wrote about wasps as generalist pollinators (The Buzz on Pollination is Not All About Bees: Wasps Are Pollinators Too!). Today, let’s look at a very specialized type of wasp and its role in pollinating fruit.

Do you love dried figs as much as I do? Well then, thanks to tiny wasps are in the order! In fact, through their evolutionary history, fig trees established a pollination system that is among the most fascinating that exist. Even though we eat only a very small number of them, there are hundreds of fig species, and each one is pollinated by one or a few species of tiny wasps from a family called Agaonids.

fresh and dried figs
Dried and fresh figs. Photo: Pixabay

These wasps are specialized in pollinating fig flowers, with a type of pollination interaction called ‘nursery pollination’. In this type of pollination, the wasps offer the service of pollination in exchange for a place to raise (‘nurse’) their offspring. But how does this work?

Let’s start by saying that a fig is like a sunflower that has been turned into itself, with all their tiny flowers facing to the inside of the fig. Some of these flowers are only female (those will make seeds), and some are only male (they offer pollen).

When visiting figs, the female wasps enter and find the female flowers. Using their long ovipositor (their organ for laying eggs), they lay one egg in it. After doing so, they take some of the pollen they previously collected on the male flowers of a different fig and they actively push pollen into the flower. While doing so, they make sure that the female flower is pollinated, and that the flower tissues grow and mature, which is what their offspring will eat while they develop inside the flower. When the offspring emerges from what was the flower, they reach to the male flowers and collect pollen, after which they leave the fig and start searching for a different one to start the cycle again.

fig fruit
Fig fruit. Photo: Pixabay

Now, you may be thinking that this system can’t work. If the offspring eats all the female flowers (where seeds are!), then the plant has none left for their reproduction! You are right!

Well, it turns out that the plants have found a way around. Among all the female flowers available to the wasps for their egg-laying, some are short and sterile, and some are long and fertile. While the short ones are the ones that wasps can develop in, the long ones will not lead to any larval development.

The female wasps can’t know which one is long or short, so they just try to lay eggs and pollinate all the female flowers. Only some of their offspring will survive. By doing this, the plant sacrifices some flower tissue in exchange for the pollination of all the fertile flowers.

If nobody cheats, both the plant and the wasps benefit from the interaction, with the wasps having a safe place for some of their larvae to develop, and the plants having a safe means for pollen transfer and seed production. Isn’t pollination fascinating?

fig wasps
Fig wasps entering the fig through the fig ‘entrance’ – the ostiole (left). Female fig-wasps laying eggs within the figs (center) and later emerging from the sterile female flowers (right).

And to end this blog today, let me tell you a story. It turns out that most fig species are tropical and subtropical, and thus there are not many fig species native to the continental US. However, we love figs, and thus farmers from California decided to try to produce figs there since the climate is very appropriate for fig tree growth. These fig trees that we eat are from varieties of the species Ficus carica, originally from the Mediterranean/Middle East.

At the end of the XVIIIth Century, farmers in California were trying to produce figs, but with little to no success. Eventually, researchers realized that those cultivated figs did not produce fruit if the flowers had not been pollinated. Wasp pollinators were needed to accomplish that. By the end of the XIXth century, the wasps associated with Ficus carica in their native Mediterranean range were imported and introduced into the USA. Figs containing larvae of the wasp species were then left in baskets close to the planted fig trees, letting the females emerge from the figs and pollinate the cultivated Californian trees. After doing this, the fig production picked up, and today a similar technique is still used in those varieties of figs that need pollination for fruit set (for example, the Smyrna and Calimyrna varieties). Today, California is the world’s third top fig producer. Talk about the economic value of pollinator wasps!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park

The Elusive Fig

Maryland Grows10 Comments

Figs
Container of fresh-picked figs. Eat at once as they only hold up for 12-24 hours on the kitchen counter. Do not refrigerate!

Fig questions have been pouring into the Home & Garden Information Center’s Ask an Expert service this fall. One reason for this, I think, is that most of Maryland’s fig trees were not “killed to the ground” during the relatively mild winter of 2016-2017, and were, therefore, able to produce good crops on the new shoots that grew from trunks and branches.

Fig Bush
Multi-stem fig bush 8-10 ft. in height

We were not so fortunate during the winters of 2014-2015 and 2015-2016. Prolonged freezing weather during those winters killed most of the above-ground plant parts. (Fig wood is damaged when temperatures drop below 20⁰ F.) Gardeners were left to cut and remove the dead trunks and branches.

The good news is that fig root systems almost always survive even the coldest winters. The bad news is that the new shoots growing from the roots the following spring rarely produce a crop. Frequently you’ll see many small green figs develop in summer that do not fully enlarge and ripen before the first frost.

Some common fig questions this year: Continue reading →

Blueberries and Micromesh

Maryland Grows1 Comment

Long-time readers may remember that last year, after about fifteen years of successful blueberry harvests (meaning that the birds got no more than about twenty percent of the berries), I harvested absolutely none. Those I consulted who are in the know said that catbird populations were way up, and certainly they are fond of blueberries.

With the thought that all those well-fed birds likely had lots of babies, and would be back, I decided to take on the challenge of protecting a row of blueberry bushes that are part of my front yard landscaping, surrounded by other plants. I drove some rebar into the ground at intervals of several feet, put pieces of PVC pipe on top of them, and capped those with some pipe caps we had sitting around from a previous fencing project. Then when the flowering was done and the berries forming, I covered the whole thing with a big piece of Micromesh. (Link is to Gardener’s Edge, which is one place you can find this product. I have also bought it from Territorial Seed, but they don’t currently seem to have the 16’x16′ size I needed. I don’t mean to promote any particular product or company over others, so if anyone knows other sources, or other similar products, please leave a link in the comments.)

Micromesh has advantages over bird netting and floating row cover. It doesn’t tangle like bird netting, and it is tougher than row cover, unlikely to tear with reasonable use. Also, plants under it don’t heat up as they can even under lightweight floating row cover. The only disadvantage is that it makes an awkward and kinda ugly intrusion in the landscape:

But who really cares as long as you get blueberries, right? I’ll be able to take it off when the fruit is done, and maybe next year I can make it look a bit better. Here’s a closeup:

I’ve fastened the Micromesh to the pipes with the snap clamps you can buy for the purpose. And I have indeed been harvesting plenty of blueberries:

Two birds (both cardinals, a male and a female) found their way under the covering, and I had to let them out, but as far as I know those are all the incursions.

By the way, I also lost all my black raspberries last year (again for the first time), and meant to get the newly-organized planting netted this year, but didn’t get around to it. So I tied up a bunch of that shiny red-and-silver tape that is supposed to keep birds away because they think something’s on fire. Ha, no way. Birds are smarter than that. A friend says she is having good luck with one of those fake owls, so I may try that next. And come October I will look for some of the motion-activated Halloween decorations to bring out again in June. Mwa-ha-ha-ha-ha-ha.

By Erica Smith
Montgomery County Master Gardener