The fight against spring frosts in Poland is slowly coming to an end, prompting initial summaries. Compared to the 2024 growing season, which in our fruit-growing region – Powiśle Lubelskie – was marked by an even earlier start of vegetation than in 2025, the current season also brought better overwintering conditions for plants, floricane raspberries. Nevertheless, frost protection proved to be just as crucial for farm profitability as in previous years. In fact, for many growers, it was a “fight or perish” situation – as two seasons with very low profit can push any farm toward collapse.
It all began on March 15, with the covering of floricane raspberries grown without shelters, as they were slowly beginning to vegetate. Initially, a single layer of agrotextile with a weight of 23 g/m² was used, and in early April, an additional layer of the same material was added. In the meantime, the supporting structure was gradually expanded and reinforced to minimize contact between the agrotextile and the canes, especially the buds.
The goal was not only to reduce the risk of the agrotextile rubbing against the buds—which, as our experience shows, can lead to bud damage—but also to prevent the canes from tearing the fabric. This issue is particularly noticeable with the Polish variety Przehyba, which has numerous sharp thorns. In this regard, the Scottish varieties Glen Ample, Glen Mor, and Glen Carron are much less problematic, as they are thornless.
Covering proved especially effective for early varieties such as Glen Mor and Przehyba, which were most vulnerable to the first temperature drops in March and April due to their early start of vegetation. A similar situation occurred during the 2024 season, when these same varieties, having begun vegetation very early, were exposed to severe frosts and were often damaged—sometimes up to 100%.
The most noteworthy moment during the raspberry covering period with agrotextile occurred between April 3 and 7, when exceptionally low temperatures were recorded. During this time, virtually all species of fruit trees and shrubs in Poland required protection. Unfortunately, the available frost protection tools were severely limited, as the conditions resembled winter more than spring. Low temperatures, strong winds, and precipitation—including rain and, in some areas, even snow—made it extremely difficult to use fogging, fire pots, or overhead irrigation.
Overhead irrigation was particularly risky due to very low daytime temperatures as well. In many cases, it had to be used not only at night but also into the late afternoon hours to raise temperatures and melt the ice from the plants. Growers who opted for sprinkling generally did not harm their crops, but they also did not achieve clear benefits—so the results were inconclusive.
The photo was taken on April 12 at 12:40 in a nearby orchard with the sprinkler still on.
At our farm, we were faced with a difficult decision at that time: whether to begin protecting primocane raspberries—whose young shoots had just emerged from the soil—by covering them with agrotextile despite the extremely challenging conditions, thereby exposing them to high fungal disease pressure due to the warmth and humidity under the cover, or to forgo protection altogether. In the end, we chose the latter: we decided not to cover them and instead removed the first shoots. We then proceeded with intensive stimulation of the root system through mineral fertilization and the application of humic acids. The goal was to quickly encourage the growth of new, stronger shoots.
On the night of April 8 to 9, when weather conditions—particularly at night—became more predictable and another frost threat emerged, we decided to begin active protection of the floricane raspberry plantations that had not yet been covered with agrotextile. Up to that point, we had limited our efforts to soil-applied treatments: boron, zinc, humic acids, and biostimulants based on plant-derived amino acids, seaweed extract, and the product Asahi SL.
In our assessment, foliar treatments at this stage of development—when the leaf mass was not yet fully formed—would have been largely ineffective. Therefore, we decided to focus on stimulating the plants through the root system to support their overall condition and enhance their resistance to the upcoming thermal stress.
The frost protection during the night of April 8 to 9 was based on lighting fires made of apple wood and peat briquettes. For raspberries covered with agrotextile, we additionally decided to use heating candles (heat sources), which were placed inside the covered rows.
In the case of floricane raspberries, our preparations for combating spring frosts actually began as early as mid-August, when we actively start preparing the bushes for winter dormancy. This includes soil fertilization with potassium sulfate and foliar treatments primarily based on silicon, potassium, boron, zinc, manganese, and copper—while also ensuring effective protection against pathogens and pests. An important aspect is minimizing soil fertilization with amide and ammonium nitrogen to nearly zero. Due to their longer transformation time in the soil before becoming available to plants, these forms of nitrogen could stimulate prolonged shoot growth and delay the onset of dormancy. For this reason, during flowering and harvest, only nitrate-form nitrogen is used.
In our case, a series of three foliar treatments using high doses of copper oxychloride—modeled after nursery practices—plays a particularly important role. These treatments induce controlled oxidative stress, which stimulates the plants’ natural defenses by increasing the activity of enzymes responsible for lignin synthesis. As a result, the lignification of shoots is accelerated, and the transition into winter dormancy is smoother—even under unfavorable conditions.
Additionally, we have developed our own highly effective solution that further inhibits shoot growth: trimming the shoot tips once they reach a height of about 2 meters. An added benefit of this method is that it prevents the formation of long internodes, which are typical of overgrown shoots. This results in a higher density of dormant buds within the retained fruiting zone after spring pruning. For yet another consecutive season, we have observed excellent results from this practice, as evidenced by the high concentration of buds at the shoot tips.
In mid-April, due to the large leaf mass developed by the summer raspberries, we ended frost protection using agrotextile and simultaneously began preparations for covering the autumn-bearing raspberries, which had by then developed new shoots. In the case of summer raspberries not involved in biostimulation trials, we gradually shifted from soil applications of biostimulants to foliar applications. These were additionally supplemented with fertilizers containing boron and zinc, and depending on the stage of development, NPK fertilizers such as 18-18-18+MgO, 12-12-36, and 13-40-13. Potassium is particularly important during this period, as it lowers the freezing point of cell fluids and makes ice crystal formation more difficult. Boron strengthens cell walls, making them more flexible during freezing and thawing, and also supports sugar transport and tissue regeneration in growth zones, speeding up recovery after frost damage. Zinc, on the other hand, activates the antioxidant system by removing reactive oxygen species generated during thermal stress, stabilizes proteins and DNA, and supports the synthesis of growth hormones, helping plants better withstand sudden temperature drops.
The nights of April 26–27 and 27–28 brought another round of temperature drops. During this time, autumn-bearing raspberries were protected with a single layer of agrotextile weighing 23 g/m². At that stage, agrotextile with a width of 1.20–1.60 meters was still sufficient. However, during the frosts that occurred just a few days later, it would have been more optimal to use wider fabric—such as 6.35 meters—due to the size of the raspberry bushes and the potential need to add a second layer. For summer raspberries and apple trees, we decided to use overhead sprinkling as the method of frost protection.
In the floricane raspberry plantations, we used Flipper type sprinklers, chosen for their lower water output and relatively easy installation on the existing support structures in our fields.
In the case of apple orchards, depending on the location, we used three types of sprinklers from the Rivulis brand. The primary ones were Flipper sprinklers and the NaanDanJain 233 PC 4.5 with adjustable spray radius (so-called sector sprinklers). These are among the most commonly used solutions in orchards across Poland. The final type of sprinkler, tested on a small area, was the Super XL. Like the two previously mentioned models, it performed its function effectively. Our only current concern with this model is its relatively slow rotation speed.
An interesting observation from drone flights over irrigated orchards at other farms was the issue of maintaining proper pressure and water volume in sprinkler systems—something that, as it turns out, not everyone manages effectively. One aspect is selecting the appropriate number of sprinklers, the correct length and diameter of the water supply pipes, and of course, the pump itself, which is absolutely crucial. But another factor is whether some growers are unintentionally undermining their own efforts by placing sprinklers too close together in an attempt to eliminate so-called “dead zones.” This often ends up reducing the maximum spray radius when the system is not sufficiently efficient, resulting in more dead zones and lower overall irrigation effectiveness than if the sprinklers were spaced closer to the limits of their maximum range—with a buffer of about 2–4 meters. As a result, one often gets the impression that a large number of sprinklers are not operating at their full potential.
In the case of Flipper sprinklers, the need for proper filtration of physical impurities from the water becomes especially evident. In our case, we use Rivulis-brand disk filters—specifically, the F7000 and F7050 models. It’s also important to keep in mind that any leftover plastic debris from the installation process, if not flushed out, will almost certainly lead to sprinkler clogging sooner or later. Based on our experience, a good practice during installation is to leave the water supply tubes from the main pipe to the Flipper slightly longer. This allows for the hose to be bent temporarily—even while the irrigation system is running—to clean out a clogged sprinkler or, preferably, to quickly replace it. In practice, this method proves to be the most efficient: with just a few extra Flippers kept in reserve, clogged sprinklers can be swapped out instantly in the field and later cleaned at the farm, without disrupting irrigation. This approach has worked best for us, and unfortunately, we’ve had to use both cleaning and replacement methods many times. If you’re irrigating large areas and want to quickly verify that the system is functioning properly, the optimal solution is to use a drone equipped with a thermal camera—such as the DJI Mavic 3 Thermal—or at the very least, high-powered flashlights for night monitoring.
Starting on the night of May 6, another cold front moved over Poland, putting everyone on high alert. In the area of our farm, frosts occurred on the nights of May 6–7, 7–8, 8–9, and 12–13. Unfortunately, in many other regions of the country, the frequency of temperature drops was even higher, with frost threats reported as late as May 18—costing many sleepless nights, ourselves included.
The 2025 season can undoubtedly be considered exceptionally challenging in terms of frost occurrences. What proved especially important was having protection systems in place that could be activated instantly—at the push of a button—without the need for daily, time-consuming preparations.
The weather this season proved to be unpredictable—even locations just one kilometer apart experienced completely different conditions. In one area, cloud cover delayed the onset of frost until 2–3 a.m., while in another, under clear skies, temperatures dropped below zero before midnight, briefly rose, and then plummeted again suddenly.
Such situations highlight just how essential local weather models are—ones that provide accurate forecasts tailored to specific areas. Unfortunately, we will likely have to wait a bit longer for their effective implementation. In the meantime, having weather stations or at least sensors that measure air temperature and humidity has proven to be extremely helpful—ideally including a so-called wet-bulb thermometer, which provides additional data critical for determining the right moment to activate irrigation systems. Access to measurement data should be remote—via a smartphone app—which significantly saves time and energy by eliminating the need for frequent trips out into the field.
In the case of systems relying on combustion engine pumps—which can be unreliable—it is advisable to have at least one backup pump available. For systems equipped with submersible electric pumps, it’s worth considering the purchase of a generator. In the event of local power grid overload, the risk of a power outage becomes very real, and having a generator can ensure uninterrupted operation of the frost protection system.
What brings us the most satisfaction is the development of an effective frost protection strategy for summer raspberry cultivation. As long as we have a sufficiently developed support structure early in the growing season, our focus should be on covering the rows with a double layer of 23 g/m² agrotextile. As soon as conditions allow, we should switch to protection using Flipper sprinklers. Interestingly, we were strongly discouraged from both covering raspberries with agrotextile in open-field cultivation and from using overhead irrigation. Yet, the raspberries withstood a total of six nights of sprinkling without any broken branches. Our only concern was safeguarding the root system against soil-borne diseases due to the large amount of water delivered to the soil—which, as it turned out, was minimal compared to the rainfall that arrived in the second week of May.
The work, however, never truly ends. After a period of intense frost protection and unfavorable conditions for carrying out other tasks—such as soil fertilization and crop protection—there is much to catch up on. This is especially true for crops irrigated with sprinklers, where nutrients have been leached deeper into the soil profile. The situation is further complicated by the previously mentioned heavy rainfall and cold temperatures.
Let’s hope that following the current spell of unfavorable weather—marked by lower temperatures, strong winds, and rainfall that began on May 14 and is expected to last for several days—we’ll see a return to sunny and stable conditions.
P.S. When planning frost protection, let’s not forget Murphy’s Law: “Anything that can go wrong, will go wrong.”