Not every growing season is the same as the previous year’s. Every year brings new challenges that may not have played a role, or only a minor one, in other years. Markus Kobelt once admitted that, even at Lubera’s two production sites, almost all the mistakes we describe below have been made at some point. Which is not to say that they should be repeated all too often.😉
Unloading young plants
Last spring, we were able to harden off almost all young plants under UV light in our polytunnel for at least 7–10 days before dispatch, and only then send them to you, our customers. However, depending on the transport distance and duration, this effect is once again negatively impacted. The young plants are kept in the shade of the CC; the hardening process begins to diminish again. If the young plants are then left on the CC for a further few days or weeks until final processing, the hardening effect is completely negated and, under certain circumstances – on sunny or hot days, or on days with a high UV index – sunburn may occur. We therefore recommend that, if potting is not planned immediately, the young plants be unloaded straight from the CC onto a lightly shaded area. A polytunnel is perfectly adequate for this purpose. A glass greenhouse should be avoided, as (almost) no UV light passes through it. Unloading also ensures that all young plants can be watered thoroughly and evenly.
Cutting young plants
Our aim is to supply young plants that are ready for potting straight away. We therefore prune our young plants at least once before dispatch, and usually several times. Through regular pruning, we aim to produce young plants that are as vigorous and sturdy as possible and which – depending on the specific crop – already show some branching. Furthermore, regular pruning allows us to maintain the young plants at a height that enables space-saving dispatch on CCs. We only supply unpruned young plants in exceptional cases, and primarily at the customer’s request.
It is therefore rarely necessary to prune our young plants before potting. Even if some of you may be itching to get stuck in, you should not be tempted to make a rash cut.
And if you do prune – even later in the growing season – the following rule must always be observed: with raspberries in particular, it is important never to prune them back to bare stems; intact green leaves should always remain on the plant after pruning. Pruning back to bare stems during the growing season inevitably leads to a (too) high failure rate.
It is equally important not to prune young plants immediately before potting. This removes the hardened leaves, and the lower leaves may suffer damage from excessive exposure to the sun.
The ideal potting depth
Even though things can get hectic in spring and early summer, you should always keep an eye on the correct potting depth. Admittedly, there are one or two crops in the range that are more forgiving of mistakes in this regard. However, a young plant potted too deeply will always have a more difficult start than a young plant potted at the ideal depth. It is particularly important to pay attention to the potting depth if the pots are to be mulched afterwards. In that case, a young plant that is perhaps only slightly too deep in the pot can quickly end up buried. Incidentally, our sister company Lubera has also had to learn this the hard way: as the stems of rhubarb plants potted too deeply can simply rot, all the freshly potted young plants that had already been covered with mulch had to be uncovered by hand. The result: with the exception of one variety, the success of the crop was secured at the very last minute.
There is a separate section on ‘mulching’ further down.
Substrate quality
When it comes to growing media, every gardener probably has their own opinion. However, there are a few basic principles on which all gardeners can agree.
- Good drainage
- Good structural stability
- Low proportion of fine particles (fine particles can be washed out and hinder drainage in the pot)
- Appropriate fertilisation when using nitrogen-depleting additives to counteract nitrogen fixation
- Appropriate fertilisation when using high proportions of compost – compost naturally has a high phosphorus and potassium content
- Use fertilised substrates quickly
- Initial analysis of nutrient levels
Limits to fertiliser stockpilling
In addition to the points mentioned above regarding the substrate, the fertilisation of substrates is also a recurring major topic. In conventional production, this usually takes the form of coated slow-release fertiliser. In organic production, horn shavings are a popular choice. As mentioned above, a fertilised substrate should be used as quickly as possible to avoid plant damage caused by excessive salt content. This applies to both conventional and organic production.
In organic production in particular, we repeatedly see that several kilograms of horn shavings are used to ensure a full supply of nutrients throughout the entire growing season. Ultimately, each farm or grower must determine for themselves exactly where the limits lie. However, the nutrient supply should be checked at regular intervals, not least to enable a swift response if necessary.
Particularly during hot spells – such as those we have already experienced in abundance this year – high salt concentrations can easily arise if too much fertiliser is broken down or released. This may also be one of the reasons why we are observing significantly more salt damage this year than in the past. Added to this is the fact that many of the best-known manufacturers of slow-release fertilisers are experimenting with new coatings, the behaviour of which is not yet sufficiently understood.
Mulching or not mulching
This is a much-debated question, which can at best be answered with ‘It depends!’. Not every crop copes equally well with being mulched. A prime example of this is the raspberry. Neither in the nursery nor later in the home garden does the raspberry like being mulched. For raspberries, our recommendation is therefore unequivocal: DO NOT MULCH!
Some readers may now be thinking, ‘But we’ve never had any problems with that!’ We neither wish nor are able to contradict that. If the conditions are ideal, even a raspberry can tolerate beeing mulched. We have only limited influence over what individual nurseries make of our recommendation.
For most other crops, it is standard practice in the industry to mulch the pots after potting. We have no objections to this either. However, when mulching the pots, one should also pay attention to the thickness of the mulch layer and not necessarily cover the freshly potted young plants completely. Minimum rule for potting teams: the green parts of the young plant must be clearly visible – and this applies to all potted plants.
How to respond to midsummer temperatures and heatwaves
In this exceptionally warm and dry summer, the young plants delivered will need a little more care than perhaps in other years. After a long journey or a prolonged period in transit, the young plants should not be potted out directly into the open ground where they will be exposed to the peak heat and direct sunlight. Ideally, the young plants should be allowed to acclimatise for a few days in a slightly shaded spot. A simple polytunnel is sufficient for this. It is important not to place the young plants under glass. Most glass coverings do not allow UV light to pass through, which causes the leaves of the young plants to become too soft.
Here at our nursery too, once the young plants have reached the right size, they are hardened off in a polytunnel for 10–14 days prior to dispatch, so that they can be planted directly into the open ground even in high temperatures or strong sunlight.
Water
Essentially, it doesn’t matter whether we have a dry or a wet summer. Water is always a particular concern. Too much is not good, and too little is not good either. That said, most plants cope much better with too little water than with too much. Particularly during hot and dry spells, such as the exceptional conditions we’ve experienced this summer, watering according to the plants’ needs is essential. Watering immediately after potting, especially in the height of summer, should be done promptly to prevent the young plants from suffering drought stress.
Over the past few months, we have seen on several occasions that young plants – which were still green but very severely dried out – were being repotted. This requires an extremely long watering session to restore the root ball’s absorbency and ensure it remains sufficiently moist. So please ensure that only moist trays are used for repotting.
Furthermore, our experience in young plant production has shown that many plants require significantly less water than expected when muggy conditions following thunderstorms combine with high temperatures. As a protective response, the plants close their stomata, which leads to reduced evaporation and, consequently, a lower water requirement.
Conclusion
Ultimately, a successful young plant season depends on many small adjustments. From correct unloading and acclimatisation, through the appropriate potting depth and choice of growing medium, to fertilisation and watering tailored to the plants’ needs, the most important thing is to always keep the crop and current weather conditions in mind. Particularly in years with prolonged periods of heat and drought, it is worth regularly reviewing established procedures and, where necessary, adapting them at . Those who observe their young plants closely and react in good time create the best conditions for a good start and successful further growth.
