Strawberries – starting new plants

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Vigorous, young strawberry plants produce the best berries. As strawberry cropping slows, plants produce long horizontal stems (runners). Along each runner a small plantlet begins to form and tiny white roots will appear at the base – see photos below. Vigorous runners can produce two or three plantlets along each runner. If you remove mulch from the area under each new plantlet and anchor plantlets to the soil surface by placing a stone on the runner on the parent side of each plantlet, you can produce many new plants for your strawberry patch. Anchoring plantlets in this way allows the crown of the plantlet to sit on the soil surface. (Strawberry crowns will rot if buried.) If your strawberry bed contains plenty of organic matter, all you need to do is give the bed a drink of seaweed extract tea to stimulate root growth and build disease resistance, and keep the soil damp. Otherwise, add a handful of mature compost to the soil surface under each plantlet. Each parent plant will provide nourishment to the new plants until they develop enough roots to grow independently.

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When plantlets are well established in autumn, the runners connecting them to the parent plant can be cut, and the new plants can be left where they are or transplanted to a new spot.
Tip: While strawberries are still cropping, place a marker beside the plants that produce the best berries and only use the runners from these plants to improve the quality of produce in your strawberry patch.

Luscious strawberries

strwbclsup1 A recent article published in BFA’s electronic newsletter, The Organic Advantage, quoted recent US research comparing organically-grown strawberries with those grown by conventional methods. Not surprisingly, the organic strawberries came out best for flavour, nutritional value, health-protecting antioxidant levels and colour, and stayed fresh for longer. The research was conducted across 26 farms and concluded that, not only was the organic fruit better, but the soil on the organic farms was higher in carbon and microbial activity, and had higher concentrations of trace elements. Soils on organic farms were also 30% higher in nitrogen than soils on conventional farms where synthetic nitrogen fertilisers were used.
There is nothing like the taste of organic strawberries. This probably has a lot to do with the fact that organic strawberries do not contain residues of the systemic pesticides and fungicides that are used on conventionally-grown strawberries.
I remember reading that strawberries were first discovered growing at the edges of pine forests in the northern hemisphere. This fact indicates three things, – that they will appreciate some shade from Australia’s intense summer sun; that they prefer a soil that is on the acidic side, and that they are dependent on mycorrhiza fungi in soil to assist them to absorb nutrients and moisture. Mycorrhiza-dependent plants absolutely thrive in organic cultivation because the humus in organic soils provides a habitat for beneficial mycorrhiza fungi.

When your strawberry plants start to flower, give them a drink of seaweed extract diluted to weak black tea strength. Kelp provides a good supply of potassium and a range of trace elements that are important in the formation of sweet fruit. The potassium also strengthens plant cells to improve disease resistance. Eco-cweed, Acadian, and Natrakelp are all products registered for use on organic gardens.
Water plants early in the day, too. Wet leaves at nightfall provide more suitable conditions for fungal diseases to establish.

Strawberry tips

For future reference, here are some general tips for growing strawberries.
• Strawberry plants should be replaced every 3 years as young plants are better croppers.
• The bed should be positioned where it receives winter sun, as shaded foliage in cool conditions does not dry quickly, and wet foliage encourages the establishment of several diseases.
• Choose a bed that that is rich in organic matter and has not contained any of the tomato/potato family for 3 years.
• Prepare the strawberry bed in early to mid summer with compost and well-rotted manure covered with a thick layer of mulch. Compost has a pH close to neutral and the break down of the manure will make soil slightly more acid, which strawberries prefer.
• If you don’t have a lot of compost to spare, starting preparing the bed in early summer by sheet composting manure (without lime) under a thick layer of mulch. Strawberry plants respond well to organic cultivation as beneficial fungi in organic matter help keep soil diseases under control and provide roots with nutrients.
• In autumn, plant out strawberry runners from only healthy plants that have produced well. I find that Full Moon phase is best for planting out strawberry crowns. See post on Propagating strawberries
• I don’t recommend growing strawberries in beds covered with black plastic. Strawberries need regular watering, and an occasional dose of liquid fertiliser applied to soil. A plastic soil covering requires drip irrigation to be set up before planting. The plastic not only makes it difficult to apply supplementary fertilisers and clear blocked drippers, it also gets very hot and can also burn fruit in many areas of Australia.
• Manures will provide the nutrients the crowns need for strong roots and good foliage growth. Good foliage cover is important to protect fruit from birds. If growth seems slow, an application or two of weak manure tea will help. But, don’t overdo it. Excess nitrogen will attract aphids that carry virus disease.
• In warm climates, plants will grow quickly and produce fruit through the cooler months. In warm temperate, temperate and cooler climates, fruit is produced through spring or summer. In cold areas, plants can be protected from frost by covering them with clean straw.
• When flowers start to form an application of seaweed extract tea will help both fruit quality and disease protection. Several flowers will produced at the end of stout stems, which stand above the foliage. If plants have produced good foliage, after flowers are pollinated, the weight of the fruit will gradually bend the stems until the berries are protected by the foliage.
• Excess watering as fruit forms will result in watery strawberries.
• If you have not mulched the bed to conserve moisture, clean straw or wood shavings should be placed under developing fruit to keep it clean.

Strawberry crops

strawb2.jpgOur strawberries are producing exceptionally well this year. So far, they have supplied a steady crop, and a couple of times I’ve harvested 3 kilos in a week from our 1 x 2.5 metre patch, – and that doesn’t include the ones that the slugs have dined on. (I’ve been so busy I haven’t got around to putting in a couple of beer traps yet.) The patch has produced far too many strawberries for us, and the excess has been made into jam, or frozen (in 500g batches) for strawberry daiquiris at Christmas or for further batches of jam. When I prepare our next strawberry bed, I will make it smaller because the grandchildren now have their own strawberry patch.

I’ve had several questions recently about growing strawberries. In cool and temperate areas, strawberries are fruiting or coming into fruit while in warmer climates strawberries produce best through the cooler months. At this time of year, there are a few things you can do to improve the quality of your strawberry crop.
• Maintain regular deep watering – but don’t over-water fruiting plants – use the finger test to check soil dampness.
• Pick fruit regularly. Rotting fruit encourages disease.
• Place a plant marker beside the best producers so that you can take runners from the healthiest plants when cropping finishes.
• If you notice fruit is becoming sunburned, you can set up a tent fly of 30-50 percent shadecloth to protect fruit from the sun during the hottest part of the day. The fly has to be high enough to allow good air circulation, or foliage diseases can occur. The tent fly also deters birds that love eating strawberries.
• A drink of seaweed extract tea, applied to the soil around the plants will build resistance to disease and improve the quality of fruit.
• If plants have leaf spot, remove and dispose of damaged leaves in a sealed plastic bag, then spray foliage mid morning with one cup of strained chamomile tea diluted to 500 ml. and, in future, only water plants early in the day.
• Add a couple of beer traps if snails or slugs are a problem. See Snails and slugs
You can start preparing next year’s strawberry bed next month, and I will post some tips on getting the best out of your strawberry bed.

Strawberry table?

C & D have asked do strawberries need direct sunlight in order to produce flowers – consequently, fruit? They refer to a segment on ABC’s Gardening Australia program that demonstrated a “strawberry table” where strawberries are planted directly into slashes made in a premium bag of potting medium. C & D are concerned that direct sunlight would cook all the good nutrients out of it the soil in the bag, and ask if dappled shade would be more appropriate.

The answer is this question is that a lot depends on the climate where the strawberries are grown. Some warming of the potting mix could be helpful in areas with a short growing season, such as Tasmania. Or, where strawberries are grown in winter to avoid fungal diseases encouraged by high humidity in summer. However, dappled shade would be more suitable in areas where days can be quite hot while strawberries are growing, flowering and forming fruit, in order to prevent not only cooking the mix, but also the plant roots.
In warm conditions, it is not necessary for strawberries to be in direct sunlight to form ripe fruit. If you observe how strawberries form, each flower cluster sits above the foliage. After pollination, the weight of the developing fruit pulls the cluster downwards until, quite often, the fruit is completely hidden by the foliage, and it reaches full ripeness.
In fact, as soon as our strawberry plants start forming flowers in mid spring, we place a 50% shade cloth canopy over them, positioned high enough to allow good air circulation. Otherwise, fruit not hidden by foliage becomes sunburned and inedible. The canopy also deters birds from eating the fruit. We have also had potted-up spare plants produce sweet, red fruit when grown in our shade house where they only received 50 % light through their entire growth period.
I can see a couple of problems with growing strawberries in a “table”. First, strawberry roots should be fanned out at planting, and this could be difficult to do if you have restricted access to the medium. Secondly, the bag would need holes punched along the underside to prevent the mix becoming waterlogged. Poor drainage will weaken the plants. Also, you would have to slash the bag open when runners start to form if you wanted to increase the number of plants. Strawberry plants should be replaced every two or three years.
If you would like to try this form of strawberry cultivation, avoid using a potting mix that contains a lot of mushroom compost as this is usually heavily limed and strawberries prefer a slightly acid medium. Debco make a certified-organic potting mix that would be suitable for this type of project. It is available from Bunnings stores. Unless conditions are cool, position the “table” where it gets any direct sun early in the day, rather than afternoon, and pack straw around the plants and the bag, if you feel the mix is getting too warm. However, I think growing strawberries in hanging baskets would be easier in warm conditions if lack of space were a problem – and the fruit would be safe from snails and slugs.

Propagating Strawberries

In our area, propagating strawberries is usually a February job, but plants were late sending out runners this year due to the cooler summer. I like to use runners to grow some new plants each year, as vigorous, young strawberry plants are healthier and more productive. Once the new plants are growing well, I can thin out some of the older plants that are no longer performing well.
While our strawberry plants are fruiting, I put a plant marker next to the best producers. As soon as our strawberry plants finish fruiting and start to send out very long thin stems, I clear away the mulch to make it easier for the plants to take root. I then give the bed a drink of seaweed extract tea. Seaweed contains compounds that encourage root growth and build disease resistance.
At the end of each runner a small plant will form and tiny white roots will appear at the base (see photo A). Vigorous runners can produce two or three plantlets along each runner. I anchor plantlets from the best parent plants to the soil surface by placing a stone on the runner on the parent side of the plant. If the plantlet does not make good contact with soil, the roots will brown and the plantlet will die or grow poorly. Merely anchoring the plantlet to the soil surface allows the crown of the plant to sit on the soil surface where it should be. Strawberry crowns that become buried will rot.
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When the plantlet has produced a strong root system (see photo B), the runner connecting it to the parent plant can be severed with secateurs or a sharp knife.
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The new plant can then be left to grow where it is, or moved to another part of the bed so that all the plants have good air circulation. If I move new plants, I dig a wide shallow hole for each plant so that I can spread out the roots before covering them, and ensure that the crowns sit on the soil surface. I also remove all but one or two of the youngest leaves as this reduces any wilting after transplanting. I usually pot up some runners for spares too, just in case. Then, all that is required is regular watering and an occasional drink of manure tea until the plants are growing strongly. I don’t usually mulch them in autumn as the bare soil stays warmer and encourages the plants to produce plenty of healthy foliage so that next season’s berries will be hidden from birds.
Purists advise that runners should only be taken from plants that have not fruited because other plants are likely to be infected with strawberry virus. An aphid spreads this virus and we have never had aphids on our strawberry plants. As long as you use only runners from healthy, vigorous plants and use organic cultivation methods, there should not be a problem with runners that have fruited.