Tag: Plum Trees

In our guide to growing plums, we cover how to cultivate these fruit trees in your landscape.

And when it comes to fertilization, there’s a lot more to it than just tossing out some granules occasionally and calling it a day.

In this guide, we’re going to discuss when and how to feed your plum trees for maximum production and healthy plants.

Here’s what’s coming up:

Before you even think about buying a bag of fertilizer, I highly recommend that you test your soil.

Here’s why:

Test Your Soil

When I started out gardening, I was always told I should conduct a soil test every year but I skipped this step for a long time, assuming that if I simply applied fertilizer regularly my plants would have everything that they need.

Then, one year, I decided to take this excellent advice and test my soil.

And it was only when I saw the results that I realized that I had been wasting money by adding a bunch of nutrients to my soil that wasn’t needed.

You’ll receive the pH level of the soil as well as an in-depth analysis of all the major micro and macronutrients, along with fertilizer recommendations.

Or, send a sample of the soil to your local university’s extension office.

When you receive your results, follow the recommendations for which amendments to apply.

They’ll tell you if your soil is high in one nutrient and low in another so you can add what’s needed without adding what’s not needed.

Choosing a Fertilizer

For your plum trees you can use either organic or conventional fertilizer, and choose from slow release or instant.

Soil feeds rather than foliar sprays work best for plums, but you can use liquid or granules to fertilize the earth.

Slow release fertilizer is less likely to be leached out of the soil by rain and irrigation, and is less likely to burn the roots of your trees than fast-acting liquid fertilizer.

Organic fertilizers are made from naturally occurring plant or animal sources like blood, bone, or fish meal. Well-rotted compost or manure falls into this category, as well.

When you plant your plum, remove the soil from the hole and work in whatever nutrients your soil test indicates are needed. The exception is nitrogen – you want to top-dress the earth with nitrogen.

Work in any potassium or phosphorus you need into the soil you removed, and then use this soil when you backfill the hole at planting time.

Then, top dress with nitrogen if your soil indicates that’s what you need to add.

Don’t let any of the nitrogen fertilizer touch the trunk of the new plum. tree, as nitrogen burns plant matter, so do not put a nitrogen-containing fertilizer in the hole with the plant.

If your soil is depleted in general, then you can feed your young plum trees as you would established specimens.

It’s best to feed your established plum trees in early spring just as the leaves begin to bud out and when the soil isn’t frozen solid.

Apply a second round of fertilizer in midsummer.

For the first feed in the spring, find a 10-10-10 fertilizer, like the product recommended above, unless your soil test indicates that you should use something different.

You want to apply about a cup of fertilizer for each year of the age of the tree up to a maximum of 12 cups.

Of course, if the manufacturer of the product you have selected suggests otherwise, defer to their recommendations. Different formulations require you to apply different amounts.

Sprinkle or soak the fertilizer evenly around the plum tree, starting a few inches out from the trunk and out to the drip line of the tree.

If you picture the canopy of the tree as a big umbrella, the area where the water would run off the outer part of the umbrella is what we call the drip line.

Then, in the summer a few weeks before the fruits start to ripen, feed the plums again with a fruit-specific food following the same steps.

All plum trees are susceptible to the following nine pests, but stressed trees are even more likely to suffer ill effects.

So it’s important to do your best to keep your plum trees happy. If you need a primer about how to care for plum trees, read our guide.

You might also want to go over our guide to how and when to spray plums for pests.

Then, come back here, and we’ll talk about the creepy crawlies that are out there eyeing your trees.

Here is the “most unwanted” list that we’ll be going over:

Our first plum pest is itty-bitty, but don’t let that fool you. They can cause big problems.

1. Drosophila

The spotted wing drosophila (Drosophila suzukii) feeds on the fruits of grapes, stone fruits, including plums, and brambles.

The adults are little fruit flies, but unlike those that devour overripe fruits on your countertop, these pests attack fruit that is just ripe and still on the plant.

The adults lay their eggs inside the fruit, so not only will there be feeding marks on the skin of the plums, but you might take a bite and get a mouthful of larvae. I don’t know what more motivation you need to try and avoid them.

These pests appear in the summer to feed and breed on plums, and then overwinter as adults to start the cycle over again.

They won’t lay their eggs in healthy plums, but they’ll look for the tiniest hole made by thrips, aphids, or mechanical damage, and that’s when they strike. The female lays her eggs, at the same time injecting a bacteria in the Acetobacter genus that causes the fruit to rot.

Even if this doesn’t cause the plum to rot, it’s likely her larvae are feeding and thriving in there.

If you notice any damaged plums, remove them immediately to deny the pests a place to lay their eggs. You can also put netting, tunnels, or cloths over your tree or shrub if it’s small enough.

You can also use a pesticide, but make sure to apply it when the pollinators aren’t out and about – an evening on a calm day is the ideal time to minimize impact on beneficial insects.

Keep in mind that pesticide applications will only tackle the adults, not any larvae already present in the fruit.

Spinosad and pyrethrins both work to kill the adults. For effective control, I recommend alternating between two products and applying every two weeks until the end of August. These pests reproduce quickly, so you need to stay on top of them.

The larval form has a flat and swollen thorax and a flattened head.

Both the larvae and the adults live and overwinter on the plum tree, though they do move in and out of the soil surrounding the planting area.

They typically target stressed trees, and the adults eat through the bark and into the sapwood, where they disturb the phloem, or the straw-like structures that move water in the tree.

A heavy infestation can completely girdle branches or trunks. These pests tend to hang out on the sunniest side of trees, so look for colored depressions and girdled branches on those areas first.

The symptoms can look similar to damage from other borer species, with frass-filled holes, discolored depressions, and weeping sap. You will also see dead branches and loose bark.

Woodpeckers love these pests and carpenter ants eat the larvae. But if you are facing a large infestation, relying on natural predators isn’t enough.

The first step is to do what you can to keep your plum tree healthy. Remember, these pests are attracted to weak or stressed specimens because they can’t feed on trees that have healthy, growing tissue full of sap.

If your plum tree is heavily infested and has multiple dead or dying branches, there isn’t much you can do.

You can try removing the most infested branches, but it’s probably better to just remove the specimen entirely.

3. Peach Twig Borer

Peach twig borers (Anarsia lineatella) aren’t super common, and they can be a pain in the butt some years and no big deal in others.

The adults are moths with mottled gray and brown wings, but they aren’t the ones that do the damage.

The white larvae emerge in the spring from their nests on the plum trees to tunnel into the young, growing shoot tips. As they age, they turn dark brown with white bands and are half an inch long.

The twigs they tunnel into eventually die, and ooze sap out of the tips.

Then, the larvae pupate, adults emerge, and the cycle continues with a second generation. This time, the larvae tunnel into the developing fruit, entering near the stem.

Since the larvae become active based on environmental temperature changes, you’ll need to talk to your local extension office to figure out when to treat your plants.

You can learn more about peach twig borers in our guide.

4. Peach Moth

The peach moth (Grapholita molesta), which also goes by the outdated epithet oriental fruit moth, has become an increasingly significant problem in North America in recent years.

They can produce up to six generations per year, which means a pretty steady infestation of the damaging larvae.

The adults are gray night-flying moths about half an inch long, but once again it’s the larvae that cause all the problems. They are white with a black heads and eventually mature to about half an inch long with pink bodies and brown heads.

The larvae bore into the shoots of the plum tree and will also feed on the fruit, entering at the stem end or in protected areas such as where two fruits touch – you did remember to thin your plums, right?

If you’ve ever dealt with codling moths on apples, the damage looks the same in your plums.

Beyond the damage they do to the fruit, infested twigs will also have wilted leaves along with a gummy sap oozing out.

The plum tree responds by sending out lateral shoots below where the larvae stopped tunneling, which means a long-term infestation can result in some strangely bushy trees.

Your local extension office will calculate the number of degree hours between 45 and 90°F, which is when the larvae develop. You can reach out to them to find out when this is and when to start treating your plum tree.

Commercial orchards rely on sprayable pheromones to disrupt the breeding phase and have great success, but it only works on the adults, not the larvae.

5. Peachtree Borers

The greater peachtree or clearwing borer (Synanthedon exitiosa) is the most common and destructive borer to impact plums, and they also attack almonds, apricots, cherries, nectarines, and peaches.

This is a nasty pest to have in your garden.

The adults are moths with translucent wings that stretch up to an inch and a quarter when open, and steel blue bodies with an orange band. They are native to North America.

The females lay up to 600 eggs each in late spring and in a week or so the eggs hatch and the reddish-brown to pale white larvae emerge. They tunnel through the bark near the soil level and into the cambium layer.

When they’re present, you’ll see dying branches and loose bark at the soil level. Leaves might also turn yellow and growth can be stunted.

You’ll often notice sawdust-like frass, perhaps along with oozing sap coming out of the bore holes. Keep an eye out for pupal cases around the base of the tree, too.

It helps to keep any plants, whether cultivated or weeds, away from the base of the plum trees.

This dark brown beetle is a true weevil with a long snout and it isn’t very large, staying under a third of an inch long, but it does some seriously outsized damage.

The adults hang out underground and in plant debris during the winter.

When temperatures warm up in the spring, they crawl or fly up into the tree and start to feed on the tiny developing fruits.

As the fruits grow bigger, the females poke holes in the skin and lay their eggs. One female can lay hundreds of eggs. They also lay eggs in apples, cherries, peaches, pears, and nectarines.

Once the eggs hatch, the grubs get to work. The third-of-an-inch-long white grubs have small brown heads, and they tunnel into the center of the fruit to feed.

This feeding not only renders the fruit inedible, but it can also cause fruit drop.

To tackle these weevils, you once again need to employ a multi-pronged approach. First, lay a tarp down under the plum tree and give it a good shake.

The beetles don’t have great grip, so they’ll topple out and land on the tarp. Do this in the morning when they’re still sluggish from the nighttime, and you’ll have even better results. Then, fold up the tarp and dispose of the beetles.

You should always clean up any fallen fruit because they could be filled with eggs or larvae. Also, it helps to cultivate the soil under the plum trees in the spring to expose any larvae that have fallen to the soil.

Finally, if this doesn’t address the problem, you’ll need to spray repeatedly in the spring when the adults become active but before they have a chance to lay eggs.

The first spray should be applied when the flower petals fall from the tree. The next should be a week later, and the final one a week after that.

These pests are oval or disk-shaped and grayish in color.

The adults are fairly flat and don’t move, so you might not even notice they’re on your tree unless you look closely. The mobile yellow crawlers usually also go unnoticed.

These pests use their sucking mouthparts to feed on bark and twigs, injecting a damaging toxin as they do.

Large infestations can cause the tree to lose vigor and produce a reduced harvest or deform the fruit. It can even kill young or weak specimens.

It’s usually the sticky honeydew the pests secrete or the symptoms on the plum tree such as yellowing foliage, drying shoots, weak growth, or reduced size and number of fruits, that tips us off that something is wrong.

If you peel back the bark on green, pliable branches, you’ll find red tissue underneath.

A treatment with dormant oil in the late winter can help suppress populations of this plum pest. You can also prune off heavily infested branches.

Once the adults mature, they are covered in a waxy coating that protects them from pesticides, so these are ineffective.

Learn more about how to deal with scale in our guide.

8. Speckled Green Fruitworm

It’s lime green and speckled! It’s the speckled green fruitworm (Orthosia hibisci).

These pests overwinter in the soil and are active in the spring, when the larvae emerge and feed on leaves, flowers, and the developing fruit, leaving ragged holes and dents.

To identify these pests, hold a shallow tray or piece of paper under the plum tree and shake the limb. They’ll fall right off.

Spray a product containing spinosad or Bacillus thuringiensis when the fruit starts developing. Either product is highly effective against these soft-bodied worms.

9. Western Flower Thrips

These tiny critters (Frankliniella occidentalis) are more of a nuisance than a major problem, though they can spread diseases that cause much bigger issues.

However, in large numbers, they can cause serious damage to the fruits, especially in thin-skinned cultivars.

The yellowish-brown insects are about 0.05 of an inch long with clear wings, though you’ll have to get close to see them. The immature form looks the same but lacks wings.

These sap-sucking plum pests feed on the flowers and young fruit, causing scarring on the skin. The feeding can also lead to deformed fruit.

Unlike borers, which hide inside the bark of trees, and scale, which have a protective coating, thrips are exposed, making them easier to get rid of.

Grab your spinosad and apply it thoroughly to the trees at petal drop. That should take care of the adults and any eggs or nymphs.

Learn more about how to deal with thrips in our guide.

While many gardeners are diligent about thinning their apples and peaches, plums, with their more easygoing nature and abundant fruits, tend to be forgotten.

Don’t make this mistake! You need to include thinning in your yearly maintenance chores. We’ll talk about why that is and how you can do it, coming up.

Here’s what we’ll discuss:

Modern cultivated varieties produce a vast amount of fruit, but it can be too much of a good thing.

Japanese types, for example, are known for growing an abundance of fruits, many of them held in clusters. The trees usually drop quite a few in the late spring as a result. European types tend to be less likely to overbear, but that doesn’t mean you can ignore them.

When our trees become out of balance by producing more fruits than the leaves can handle, we need to somewhat restore the balance, and we can do that through thinning.

Why You Should Thin Your Plums

There are four reasons that we gardeners need to thin our plum trees:

1. First, the remaining fruits will grow larger than they would if you left all the ones that are developing in place.

This isn’t as essential on smaller cultivars like ‘Satsuma’ when the size isn’t as important. But on larger cultivars such as ‘Santa Rosa’ or ‘Elephant Heart,’ it’s a vital step to help the tree produce the big plums they’re renowned for.

When there are too many fruits developing on a tree, they’re all competing for energy, and when this happens, they’ll all be smaller than they would be otherwise.

2. Second, overloaded branches tend to break easily. A strong wind comes along, and suddenly, you have cracked branches dangling all over the place.

Not only does this reduce your yield, but it can expose the tree to pathogens and pests, and you don’t want that.

3. The third reason is that plum trees can bear heavily one year and hardly at all the next year, known as biennial bearing. Most of us don’t want all our harvest one year and only a few the following year.

Every fruiting plant needs to balance the energy required by the yields with the amount of leaf surface it has to photosynthesize.

But because we have bred trees to produce larger and more fruits than they do in nature, they become imbalanced. A plant that is devoting all its energy to producing fruit won’t have enough left to create the buds that will turn into plums the following year.

4. Finally, we want to discourage the tree from dropping fruits on its own. We want to be the ones to choose which to keep and which to remove.

When to Thin

Timing is everything when it comes to thinning. If you do it too early in the year, it won’t have much impact, plus at this time it’s really hard to see the fruits.

Conversely, if you wait too long, the plant will already have been drained of nutrients and energy, compromising next year’s harvest.

The right timing is between three and four weeks after the blossoms fade.

At this point, the fruits should be developing nicely so you can determine what you’re doing, but they won’t have grown to the point where they are costing the plant too much in terms of energy.

Don’t thin a tree that is producing for the first time. Give it a year to establish itself.

The Process

Plums grow on small spurs on one-year-old wood. A spur is a short little branch that only grows a few inches long.

Grab some scissors or secateurs, or just plan to use your fingers. For those that are really high up, you might opt to use a pole saw or pruner.

If you decide to use a tool, make sure it’s clean and sanitized. You can wipe it down with isopropyl alcohol or a 10 percent bleach solution.

Remove the fruit so there’s only one plum every six inches or so, though the distance between them depends on how large they will eventually grow.

For trees with larger fruits or in the case of plumcots and pluots, go with eight inches in between, and maybe four inches for those with smaller fruits.

Since it can be hard to determine distance when you’re out in the field working, measure your hand. I know that my fist is about four inches and my outstretched hand is about ten inches from the tip of my pinky to the top of my thumb.

It’s not an exact science, of course, so don’t stress about finding the precise distance.

Sometimes, you can see that the tree is favoring certain fruits over others because they’ll be larger and further along in the development process. Leave these and remove the smaller, less well-developed ones.

To remove the fruit, just cut it or pull it off right at the spur.

Don’t forget to lift up leaves and look underneath, you never know what’s hiding under there. There could be a ton of plums just out of sight.

In late spring, many types of plums, but especially Japanese ones, will drop some fruits on their own if there are too many for the tree to support. They’re smart like that. So you can leave more fruits on the tree than you need in anticipation of this event.

If at any point you see a branch that is bending or stressed enough that it’s close to breaking, go ahead and thin it even more than the guidelines above.

You can also do a bit more thinning after the fruit drop occurs if there still seem to be too many. Be aware that at this point, any impact from thinning will be minimal.

If you’re a gardener hoping to start a productive orchard with dozens of popular commercial plum cultivars, then the answer is no. You shouldn’t try this propagation method.

We’re going to talk about why that is and discuss the entire process, from cleaning the plum pit to planting your new tree.

Here’s what we’ll go over:

Before we get started, let’s define our terms. Botanically speaking, the plum is known as a stone fruit or drupe.

It’s made up of the fleshy bit we eat, known as the mesocarp, and the skin that encases it, known as the exocarp.

Inside at the center is the hard pit that we usually throw away. This is made up of the hard endocarp, and if you break it open, you’ll find the seed inside.

Plum drupes are indehiscent, which means they don’t burst open to release the seeds at maturity, unlike dehiscent species like poppies, rhododendrons, kale, phlox, and spirea, that split open allowing the seeds to drop to the ground.

Instead, the shell has to decompose naturally or be eaten by an animal for the seed to be released.

That informs how we approach growing plum seeds. So let’s answer the question of whether it’s even possible to do this, first.

Is It Possible to Grow Plums from Pits?

It’s possible to grow plum trees from the pits of the drupes, but there are a few caveats.

The fruits you obtain at the grocery store or pick from your own tree might contain seeds that are sterile. Or, if it is viable, the plum tree that emerges might not be anything like the parent.

This is particularly true of Japanese and European plums, which are usually hybrids grown on grafted roots.

That means the seeds inside the plum fruits won’t necessarily produce a tree that resembles the one you’re growing in your yard, or produce fruit like the one you purchased at the store.

For example, if your plum tree is a dwarf type, it’s grown on dwarfing rootstock. The new tree that you start won’t be dwarf, it will be standard sized. And possibly you might end up growing a tree that doesn’t produce fruit.

In the case of wild plum species like American (P. americana), beach (P. maritima), Canadian (P. nigra), or peachbush (P. texana), growing from seed is common and if you propagate a species plant you’ll produce a tree that is similar to the parent.

In other words, if you want to propagate a productive fruit tree, this isn’t the method you need to use.

But if you want to play around, have some fun and maybe breed your own one-of-a-kind fruit tree, or grow a native plum tree, then it’s the perfect method. Provided you have some patience!

Preparing the Seeds

This process takes time, so plan ahead by starting about four months before you want to plant.

If you’re propagating seeds collected from hybrid plums, start twice as many as you think you’ll need. Some seeds are duds, some are stubborn, and some will fail.

Remove the pit from the fruit and rinse it clean. You might need to use a toothbrush or veggie brush to scrub them to remove all the flesh.

They don’t need to be spotless, but you want to avoid the attached flesh rotting or attracting pathogens. You don’t need to open the endocarp, though some gardeners opt to do so.

If you want to open it, place the pit in room temperature water and let it soak for 24 hours. Then, use a nutcracker to gently pop the shell open.

During this process, if you accidentally damage the seed, which does happen occasionally, you’ll need to toss it out and start a new one.

Next, you’re going to trick the seed into thinking that it has been chilling in the ground through the winter months. This is known as stratification, and it’s a necessary step.

Why on earth would a seed need to be cold before it would be able to germinate? It’s actually a smart evolutionary tactic.

If a seed were to burst out and germinate in the late summer when it’s nice and warm, only for the weather to turn freezing just as the young plant is trying to get established, it would spell disaster.

However, several months of chilly weather tells the seed it’s safe to germinate because there are lots of warm days ahead.

You could sow outside in the fall and let Mother Nature do her thing, but we gardeners like to have more control over the process. It’s safer that way because we can adjust the temperature as needed and protect the seed from hungry wildlife.

To stratify the plum seed, moisten a few pieces of paper towel and wrap them around the seed, so it’s surrounded by at least four layers of moist paper towel.

Place this little pack in a plastic bag and squeeze the air out before putting it in your refrigerator. It helps to label the bag with the date and the type of seeds inside, especially if you tend to be forgetful, like I am.

I always tell myself I’ll remember which baggie is which, but I inevitably forget and find myself staring at a handful of stratified bags, completely mystified as to which is which or what I even started working with in the first place.

You might also want to make a note on your calendar or in your phone to remind you when the stratification time is up, at least two months but preferably three from when you first place the bag in the refrigerator.

Check the paper towel wrap frequently to make sure it’s always moist but not soggy. If the paper towel totally disintegrates, replace it with a fresh wrapping.

At some point during the two- to three-month stay in your refrigerator, the endocarp will crack open and roots will start to develop. You might also see some green growth, but not always.

Once the seeds have sprouted, it’s time to remove them from the refrigerator and plant them.

If the seeds haven’t sprouted after three months, you can try planting them, but it’s very likely that they are simply not viable.

Potting Up

Once you see those seeds sprouting, after a little celebratory pat on the back for all your patience so far, start the next step.

Gently lower the seed into the pot with the rooted end pointing down. Cover it and moisten the soil. Place the container in an area that receives at least six hours of direct sunlight per day.

This can be indoors or out, but only set them outside if the temperature is consistently above 40°F.

Keep the soil moist and wait until you have about six inches of aboveground growth, or you can see roots coming out of the drainage holes at the bottom of the pot – whichever comes first. At that point, you can transplant your seedling into the garden after hardening off.

What’s that, you ask? “Hardening off” is the process of gradually introducing the young tree to the conditions of its new growing location.

If you were to plant your baby tree out in the garden without a gradual transition process, you could shock or even kill it.

To harden off, take the plant to the spot where you’re going to plant it and leave it there for an hour. Then, move it back to where it was.

The next day, set it out for two hours before bringing it back in. Keep adding an hour each day for a week. Then, it’s ready to go into the ground.

Transplanting

The best time to transplant your seedling is in the spring or fall. Don’t transplant during the winter or summer.

Choose your location and dig a hole as deep as the container the plant is currently growing in and twice as wide.

Remove the plant from its container and gently spread out the roots. Cut off any that are broken or soggy.

Gently place the plant in the hole. It should be the same height as it was in the container. Fill in around it with soil and water well. If the soil settles, add a bit more.

Take care of your baby tree as outlined in our guide to growing plums.