MAY in the garden
To lift or not to lift?!
You do not have to lift dahlia tubers, BUT, it only takes one tuber with one shoot to produce plenty of top quality flowers. If you leave tubers in the ground then that one tuber grows a whole clump in one season. The original tuber is not likely to flower again and will probably rot. This rot can spread to the other part of the clump. The next year each tuber in that clump will produce its own clump and so on. The clump will grow exponentially and take up a great deal of space, water and goodness from the soil. The tight clustering of stems will inhibit good air flow and promote fungal issues. The tubers will eventually push themselves out of the ground due to lack of space. This exposes the tubers to the rain, frost, insects and trauma. Over a number of years the plant will likely lose its robustness, flowers will often become smaller and stems shorter and weaker. It becomes a nightmare to dig up and potentially divide. I find that dividing these mammoth clumps not worth it. I would recommend letting it shoot then take cuttings to start again.
If tuber clumps are lifted every year it is a much easier job. It is easy to check for rot and gall disease!! It allows the bed a time to rest and be suitably fertilized for over winter and perhaps putting winter flowers, veges or cover crops down. It also allows for division of tubers to either increase your numbers or to give away/sell excess. Selling tubers enables you to finance new varieties.
If you have a wet climate and/or don't have raised beds then you are likely to have trouble with tuber rot. If your babies are tucked away in bed inside they will have a better survival chance.
Towards the end of May/June is when I start to lift my tubers. Do not lift earlier as there may be tubers but not fully developed and may struggle. Even after a frost, the foliage may die back but there is still translocation of sugars going down to the tubers. Frost won't kill tubers unless they are on the surface. A buried tuber should be safe. Timing can depend entirely on the weather. If you get lots of wet and frosts it is ideal to lift the tubers out of harms way. I check for tuber rot at this time. If only part of the clump has started to rot you can remove this and then dust with sulphur powder or cinnamon. Now is also the time to check for gall. If you find any, immediately discard the clump and any surrounding dirt from where it came from in the garden. Do not compost!
You can try growing spuds in the area the contaminated plant came from to help with detox.
Clean your hands and any gear that has contacted the plant. Do not separate to isolate in a pot to wait and see! Take a picture and send to an expert for their opinion.
Gall appears as a white cauliflower like clump of growth at the crown.
Sometimes tubers can be already putting up lots of new shoots so can be difficult to tell on initial lifting. New shoots are usually individual shoots and start to have green tips that proceed to grow to length.
Gall. A bacterium that contaminates the plant, tuber and the surrounding dirt. Dispose of to the dump or burn. Lift surrounding dirt and dispose of too. You can try growing potatoes in that spot next season.Wash hands and tools that have come in contact with affected material.
These tubers, although misshapen, are fine and went on to produce good cuttings.
For further accurate information, I recommend reading Dr. Keith Hammetts' write ups on gall.
Cath Smart from Nelson is also available to contact for excellent gall information.
Lifting
I use a fork for lifting, others use a spade so as not to damage tubers. I find that my soil is friable enough to not need a spade. Gently ease tubers up and if it appears there are long roots you will need to loosen soil further from the tubers. If you just lift and yank it is very easy to break tuber necks.
Stems trimmed long enough so you can pick clump up easily. Do not pick up by the tuber. Tubers washed. (if needed) Label on. Wash only if you have sticky dirt that wont come away by a simple tap on the stem with your secateurs. You can leave dirt on if you want until you start dividing.
A soft, long bristled paint brush is good for removing the last of the dry dirt or any storage medium from the crowns.
When you first lift tubers, the eyes are easily visible. You can use this to divide as soon as you lift. This is the best time to divide. If you have too many like me and wet weather is creating havoc, it isn't practical. It does give you a good idea though of where the eyes are so you can divide midwinter. You can divide later when eyes reemerge too. If you wait until the shoots have developed too big it becomes too easy to damage them when dividing. You can of course take cuttings from knocked off shoots.
Those tubers that I have to hose off, I put on the stones to drip dry as much as possible before storing. I give them an hour or so in the winter sun. If you have to hose tubers make sure you dont water blast them too hard or you will damage the outer protective layer. Tubers can also have colour variation from pale cream, brown and even pink tinges. All are ok.
If the stems are large and/or hollow and hold water it might be an idea to initially store upside down to allow drainage.
Mild winter sun for an hour or two to dry tubers. Leaving them wet in storage will invite trouble. They will dry even quicker if divided.
If you are having difficulty drying the centres of your tuber clump, you can always tip it upside down over your bin to completely dry it. Just trim the centre stalk so it sits on the bottom of the bin so as not to put too much pressure on tuber necks.
Tuber clumps in their boxes lying on sawdust. The saw dust is dry and tubers will be divided over winter and be lain down in the sawdust. To be dampened off when inducing shoots to grow. You can use any light weight medium for storage that will retain moisture in the spring. Sprinkle slug/snail bait around the tubers as a precaution. Some also sprinkle diazanon too.
There can be many reasons not to lift; lack of time, ill health, bad weather, can't be botheredness or youv'e been told by others you don't need to, they grow just fine without lifting. These are all valid reasons at some time or another, but even if you dont lift you need to check for disease, in particular Gall, which becomes most apparent at this time of year. How do you check for Gall? Lift your tuber! Even if you only scrape away surface dirt till you can see crown area. If the plant is contaminated, dispose of it and clean your hands and clean tools. Lots of soapy water and a scrub. You can use hand sanitizer or bleach but only if surface dirt is removed.
If your plants are in containers, you can turn the buckets on their sides and leave outside out of the worst of weather and frosts. You will still need to health check at some stage over the winter. You will need to divide in the spring or the tubers will not be able to do the plant as well as it could. If you took cuttings early in the season and have those spares in small pots (pot tubers) simply turn these on their side too. The little tubers from these can be planted without dividing in spring or divided if possible. Sometimes it is too difficult to get into the little crown.
Roots can grow to extraordinary lengths. It highlights the need to be careful when digging up as it puts a lot of pressure on tuber necks. It also means that the plants are sourcing food and water from a wide area. They can also potentially be contaminated by neighboring plants with disease.
The little raised lesions are lenticles and are an indicator of lots of moisture. They are not a problem.
In spite of the weird growing season(2023), with well drained soil, tuber production is great!
The tuber clump on the right shows perfectly the original tuber planted last year and the predominance of roots coming from it that has fed the plant all season until new tubers have grown and started putting their own roots out.
Roots 75cm long!
Little white bumps are lenticels.
Parent tuber easily spotted.
After lifting is the time that I put a deep layer of compost down on the beds. This will help create lovely friable soil, that drains well and has lots of yummy food for tubers. If you want to prevent weeds over winter, I use old carpet to cover the bed. I also use pea straw and sheeps wool. Raising your beds will also help with drainage but may need more watering in flowering season.
If you leave tubers in the ground be wary of leaving pea straw mulch in place if it hasnt rotted down completely as it will retain lots of moisture which is not ideal in winter and increases the risk of rot.
If you can drop your garden fork into the soil from around 500mm high and it sinks its prongs completely into the soil you are on target with great topsoil.
The next task will be dividing.