By Susanne von Rosenberg, UC Master Gardener of Napa County
January is a great time of year to plant strawberries in Napa Valley, regardless of online recommendations to plant them in the spring, late summer or early fall.
Strawberries come in three types: June bearing, day neutral and everbearing. June-bearing strawberries set one heavy crop in late spring, typically starting in mid-May in our area for the early varieties. They produce most of their berries in a window of 10 to 14 days, and they tolerate hot temperatures. June-bearing strawberries come in early-, mid-, and late-season varieties. The late-season varieties start fruiting about two weeks after the early varieties.
Day-neutral varieties will fruit as long as the day length is 12 hours or more and temperatures remain between 40°F and 90°F. Despite their name, everbearing strawberries will produce a fairly heavy crop in late spring and again in early fall. They may produce a third crop in mid-summer in mild summer areas.
Sources disagree about which type of strawberry plants produce the biggest berries. But unless you want large berries for decorative reasons, don't let size affect your choice as it has no correlation to flavor.
Many strawberry varieties do well in our area. In 2012, the Master Gardeners did a field trial of three varieties, and Albion (a day-neutral variety) performed best. Sequoia (an everbearing variety that can produce all season in mild climates) also did fairly well, but Quinault, a popular everbearing variety, performed poorly.
Other good day-neutral varieties include Seascape and Selva. The latter is notable for its large berries. Good June-bearing varieties include Chandler, Jewel, Camarosa and Ventana.
Not surprisingly, catalogs tend to describe all the varieties as having great flavor, so just experiment and see which you prefer. One source said Jewel had an “exotic tropical fruit flavor.” Camarosa and Chandler are said to produce large yields.
Everbearing varieties seem to be losing ground to day-neutral varieties. To make matters more confusing, a lot of catalogs and online sources use those terms interchangeably, although they clearly aren't the same.
Look for certified disease-free, bare-root plants from a local nursery. Big-box stores sometimes have six-packs of strawberry plants, but often with no indication of variety. Think twice about buying these as you won't know if they're suited to our climate, or when the plants will bear fruit.
Strawberry plants will produce the year you plant them and will typically have their best crop the following season. After that, production will decline. Expect to replant about every three years. You can grow your own new plants from runners. June-bearing plants will produce the most runners, whereas everbearing and day-neutral varieties put more of their energy into producing fruit.
If you don't want to grow replacement plants, cut off the runners because they take energy from fruit production. It's also best to cut off runners in the first year to help the plants get established. Leaving a few runners to fill bare spots is okay.
Strawberry plants need at least eight hours of sunlight a day. Don't plant them where you recently grew members of the Solanaceae family, such as tomatoes, eggplants, peppers and potatoes. All these plants are susceptible to verticillium wilt, a fungal disease. By rotating where you plant Solanaceae, you can keep the fungus from getting established in the soil.
Slugs and snails are the primary pests of strawberries. Pick them off by hand, or use an iron phosphate-based bait. These baits are non-toxic to other animals. Strawberries can also suffer from nutrient deficiencies. (I had an issue with lack of boron.) Check online sources if your berries look odd.
Plant your plants so that the crown (center growing point) is just above the soil level. Strawberries need regular water, especially during fruit-bearing season. Use drip irrigation with emitters at least two inches away from the plant to minimize the risk of fungal disease. Keep the soil moist—strawberries are shallow-rooted—but let the top of the plant dry out between waterings to avoid rot. Don't plant strawberries near irrigated lawn or where they might be watered by overhead sprinklers.
Strawberries like well-drained soil. Raised beds with 12 to 18 inches of soil are ideal, or mound up your garden soil to a depth of 6 to 8 inches. If you are growing strawberries in a container, be sure they have 12 inches of soil as well. Those special strawberry planter pots are attractive but often not that effective because they don't hold enough soil. Use them for growing annual herbs instead.
Strawberries do not need a lot of fertilizer. One application of a slow-release or organic fertilizer at planting time is adequate for the first season. Fertilize again in late summer or early fall for the following year.
Workshop: Napa County Master Gardeners will host a workshop on “Pruning and Plant ID” on Saturday, January 29, from 10 a..m. to noon at Las Flores Community Center, 4300 Linda Vista Avenue, Napa. Bring gloves and wear gardening attire for this hands-on workshop. To register: https://ucanr.edu/2022JanLasFloresLearningGardenPruning
Library Talk: Napa County Master Gardeners will give a talk on “Creative Cucurbits: Loofahs and More” on Thursday, February 3, from 7 pm to 8 pm. Save room in the garden for some crazy cucurbits and learn how to prepare them for your own use or as gifts. Register to receive the Zoom link at https://ucanr.edu/2022FebCucurbits.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit https://napamg.ucanr.edu
- Author: Mark Bolda
Introduction: With the discontinuation of methyl bromide as a possibility for pre-plant soil fumigation, we at UCCE have been very active in looking for viable alternatives. One alternative, identified by the test name TRX58, having a fairly high vapor pressure and already having certain uses in agriculture, was a good one to try.
Materials and Methods: Work was done in a field known to experience pressure from the plant pathogen Fusarium oxysporum f. sp. fragariae . Application of the test material TRX58 (550 lb per acre) and the grower check of Triform 80 (34 gal per acre) was done on October 5, 2015, shanked in followed by tarping with totally impermeable film (TIF). So as to obtain adequate fumigation and coverage, both the materials were applied in blocks 22 feet wide and 200 feet long with each block replicated twice. Two strips of 11 feet wide were placed between the fumigated plots, designated as untreated checks and not treated.
Planting of the strawberry varieties Cabrillo, Albion, Sweet Ann, San Andreas and Monterey was done on Nov 17. Plots were maintained as any other on the farm with adequate fertility and irrigation. Pick stations of 20 plants per variety x 4 replicates and commencing in April fruit harvest in all plots was done once a week and fruit weighed.
Statistical analysis is as below, and broken up into two halves (April + May) and then also given as a total.
Discussion: Triform 80 is indisputably the better treatment, but it is also indisputable that TRX58 is better than doing nothing, which as one can see from the photos is not wise in this sort of situation. It is also notable that variety such as San Andreas which is known to be "resistant" (actually tolerant is the better word) to Fusarium still loses a little bit more than half of its yield in unfumigated soil. There is a strong case being made here for treatment of soil to maintain good strawberry yields.
A deep bow of gratitude to Miguel Ramos for letting me do this work in his field, to Mark Curtice from Lassen Canyon Nurseries who gave us the plants, and then to Trical who did the fumigation.
People should realize that without the efforts of all these people working together, we would be doing very little novel fumigation research right now.
- Author: Mark Bolda
A recent article referred to one of the reasons that growers need access to new strawberry varieties is that there is an inherent loss in vigor through the propagation process. That growers need access to new varieties to remain competitive is absolutely true, but that they need access to new varieties because the existing ones decline in vigor is not.
Plants do not invariably “lose their pep after years of cloning”. Indeed, reputable nurseries avoid a loss of vigor in a variety by periodically going back to meristem culture in order to keep their plant stock strong and productive. It does happen (especially in some formerly popular caneberry varieties - compare Ollalieberry in the field today to what was around in the early nineties) that older varieties of less demand don't have the meristem work done as frequently and subsequently become less vital over time.
What is meristem culture? Meristem culture is the excision of a cluster of actively dividing cells from the meristem (tip) of a newly formed strawberry runner, followed by surface sterilization, placement on a special medium, subsequent rooting, gradual acclimation of the new plant and transfer to a secure greenhouse. While some cases of genetic instability from repeatedly doing meristem culture have been noted in the literature, this cannot be described as a drift towards a loss in vigor of a variety. At any rate, programs for production of true to type (identical) plant stock using meristem culture have been used for a long time at any of the strawberry nurseries in business today.
A good example of how well and long a popular variety can be maintained through meristem culture would be the strawberry variety ‘Chandler'. Chandler continues to be widely planted by direct marketers because consumers just love its flavor and quality. Consider though that this variety was patented in 1984 by the University of California, and has had no apparent loss in vigor in all this time because the nurseries continue to go back to meristem culture to maintain it.
Growers have rumored that the variety ‘Albion' has been losing its vigor, but work at the Pomology Field Station in Watsonville over several years shows that this was not at all true. The Albion grown at this field station has experienced NO loss in yield since it was first released. Rather the rumored "loss in vigor" of the very widely planted Albion is almost certainly because of the industry wide steady drift away from methyl bromide fumigation to less effective alternatives like 1,3-D and chloropicrin.
- Author: Mark Bolda
Tuve el placer hace poco de conversar con el Dr. Doug Shaw, experto de fresa de UC Davis, acerca del concepto de enfriamiento en la fresa combinado con el deseo de unos productores de nuestro distrito de reducir esto a un nivel significativo, aun hasta cero en algunos casos.
De repaso, favor de recordarse que el requisito de enfriamiento de fresa en California consta de dos partes esenciales. Una parte es lo que acumula la planta en el campo antes de ser cosechada, y la otra es la acumulación de enfriamiento después de ser cosechado y la planta está en el frigorífico. Hay una diferencia muy grande entre los dos y uno no suplantará el otro. Enfriamiento en el campo toma lugar cuando la planta este todavía en el suelo, abajo del cielo abierto y manteniendo todas sus hojas. Enfriamiento suplemental toma lugar después de que la planta sea cosechada completamente desfoliada y ocurre en una temperatura constantemente fría y oscura (véase Foto 1 abajo).
Acumulación de enfriamiento, sobre todo enfriamiento suplemental, en el trasplante de fresa lo hace más fuerte y más hábil de sobrepasar los desafíos de ser trasplantado y el periodo productivo más allá.
Tal como se ha sacado através de mejoramiento de la fresa de UC algo de sensibilidad al enfriamiento en las variedades de Albion, Monterey y especialmente San Andreas, es posible cultivar estas variedades con cantidades de enfriamiento suplemental menor de lo recomendado de 10 a 18 días. Sin embargo, los productores quienes eligen de reducir el enfriamiento abajo de esta magnitud deben de reconocer el riesgo a lo que están entrando. Esto no es un ejercicio para novicios, de tal manera que si el clima o las condiciones del cultivo tornen desfavorables, las plantas con menos de lo recomendado del enfriamiento y el vigor careciente correspondiente sufrirán más que las plantas con lo adecuado. Aun más, mientras las variedades de UC de día neutro tratadas con menos enfriamiento de los 10 a 18 días recomendados sí pueden producir fruta más tempranas que las demás, debido probablemente a la fecha más temprana de plantación, estas plantas probablemente no producirán en forma optima en términos de rendimiento y calidad además de demostrar una tendencia de producir fruta más pequeña más tarde en la estación.
En único caso donde uno podría querría cortar el periodo de enfriamiento suplemental sería si la cosecha de los trasplantes es tan tarde que un mínimo de enfriamiento de 10 días resultará en una fecha de plantación tan tarde que se comprometerá el establecimiento y crecimiento de la planta nueva.
Afuera de eso, se mantiene la recomendación de dar a las variedades día neutro 10 a 18 días de enfriamiento suplemental.
- Author: Mark Bolda
I had a conversation quite recently with Doug Shaw, UC plant breeder, concerning the concept of chill in the day neutral varieties and the desire of some Central Coast growers to reduce the recommended amounts significantly, even all the way down to zero days of chill:
In the way of review, please recall that chill requirement in strawberry in California is made up of two essential parts. One part is what the plant accumulates in the field before being harvested, and the other is accumulation of chill after harvest and the plant is in storage. There is a big difference between the two and one does not supplant the other. In-field chill takes place when the plant is still in the soil, out in the open and still has all its leaves. Supplemental chill takes place after harvest of the plant and occurs in a constant near freezing temperature, in the dark and the plant has none to very few leaves left (Figure 1 below).
Accumulation of chill, especially supplemental chill, in the strawberry transplant makes it stronger and better able to survive the stress of plant harvest, transplant and the growing season beyond.
As some of the chill sensitivity has been bred out of the modern UC day neutral varieties such as Albion, Monterey and especially San Andreas, it is indeed possible to grow these varieties with less than the recommended amounts (10-18 days) of supplemental chill. However, those who choose to reduce chill below these amounts should recognize the amount of risk they are taking and that this is not an exercise for those still using training wheels. Should growing conditions take a turn for the worse, these underchilled plants do not have the vigor to help them pull through and will suffer more than those adequately chilled. Moreover, while UC day neutral strawberry plants chilled significantly less than the recommended 10-18 days can produce fruit earlier than others (probably owing to the earlier planting date), these plants quite likely will not perform optimally in terms of overall yield and quality along with showing a tendency to produce smaller fruit later on in the season.
The only case where one would want to go short on supplemental chilling time would be if the plant harvest was so late that a minimum chill time of 10 days would result in a planting date so late that it would compromise plant growth and establishment.
Other than that, it is still recommended to give the UC day neutral varieties 10-18 days of supplemental chill.