Salad Blue Potatoes Potting Compost Comparison

Salad Blue Potatoes are a heritage variety which I haven’t grown for too many years to mention! I picked up some seed potatoes and thought I would see how well they would grow in potato sacks rather than in the ground. Then I had the opportunity of seeing how well they would grow using different multi-purpose composts as I was given free samples following a garden press event.
What follows is a not-very-scientific experiment – comparison really, of how the potatoes grew and tasted. And to begin with, some background on this purple-blue potato.

Salad Blue Potatoes

Salad Blue Potatoes, also known as Blue Salad Potatoes, date from the 1900s and were, like many fine potato varieties, developed in Scotland. That blue, almost purple flesh, retains its colour when cooked – not always the case with coloured vegetables! The blue pigment is an anthocyanin, which is an antioxidant.

This early date makes them a heritage vegetable, or heirloom vegetable. What they are not, despite the name, is a salad potato. Salad potatoes is a synonym for first early potatoes. This is due in part to the thinner skins these potatoes have as their maturity time is shorter. The salad blue potato is a second early variety.

Having said that, if you don’t mind the possibility of the potato falling apart a little bit, the salad blue is decorative and tasty enough to be eaten as a salad potato. Similarly, it’s not the best variety for roast potatoes. Again, it makes an unusual roast vegetable to amaze and amuse guests, so you could use it this way. Presented as a mashed potato, the salad blue excels as the high dry matter content lends it a good fluffiness. I haven’t made chips with this variety but am assured they’re good.

What is an Heirloom Vegetable?

Plants which are called heritage vegetable, or heirloom vegetable pre-date 1945 – 51. So-called not because of the length of time they’ve been around but relating to the widespread introduction of hybridisation post Second World War. These heirloom vegetables are open pollinated species, varieties and cultivars.

Container Grown Potatoes

I have written elsewhere about growing potatoes in containers, so for the ‘how to’ bits check out the blog link below. However, here are some extra growing tips for you –

Containers can overheat, so avoid placing where they get the full afternoon sun. I had mine where they caught the morning sun and then had sunlight, but not direct sun for the remainder of the day.
Potatoes like moist soil, so keep them well watered in warmer weather.
Remember that when the foliage has grown to cover the surface of the container, rain will have trouble percolating through. You may need to water them even when its rained – check the soil to be sure.
You will often get smaller yields and / or smaller tubers when growing potatoes in containers. Plant according to your desired outcome. For example, if golf ball sized new potatoes are what you’re after, plant more tubers, say 5 in a potato sack. For larger, main crop tubers for jacket potatoes, plant 3 tubers in the same space. NB the size of tuber is also partly dependent in the variety.
Second earlies and main crop potatoes will benefit from being chitted, just as you would do if growing in the ground.

The Multi-purpose Composts used

As with all potatoes, Salad Blue Potatoes prefer –

a pH which is slightly acid to aid scab resistance, so pH 5 – 6 would be ideal
loose, fairly deep soil
well drained soil or growing media
nutrient rich, especially potassium and nitrogen

The two multipurpose composts I had were Fertile Fibre and Westland’s New Horizon.

Fertile Fibre has a range of peat-free soils, based on coir. Some are certified as organic by the Soil Association. They also have vegan multi-purpose composts, biodynamic composts and a reclaimed peat product which does not damage historic peat bogs.
I used the Fertile Fibre Multipurpose Compost which is a Soil Association permitted product which contains certified organic coir and no green waste. Sold as ideal for crops in containers and vigorous growth.

Westland New Horizon has a range of peat free composts for use in containers and as soil improvers.
I had the New Horizon All Plant Compost bio3. This is free from green waste and suitable for containers and productive crops. It has a pH 5.5 – 6 but is not sold as suitable for ericaceous plants as this would suggest a lower pH. The consistency of this coir based compost is very similar to a peat based compost.

Growing the Salad Blue Potatoes

For ease, I shall refer to the Fertile Fibre grown potatoes as F and the New Horizon as H. I would normally have spread this number of seed potatoes over three sacks but decided not to have a topsoil option this time.

The potato sacks were placed next to each other where they would receive morning sun and then light but not direct afternoon sunlight. Both had drainage (pebbles and grit) put in the bottom of the bags before the multipurpose compost was added. The seed potatoes were planted at the same depth in each sack.

They were watered with the same amount of water. Both received a liquid seaweed-based feed after six weeks; thereafter fortnightly.

The potato sack containing F showed the first green shoots; N followed a day later.

Initially, the F sack potatoes grew more quickly; this evened out after 6 – 7 weeks. Both presented with lush, healthy foliage. No pest or diseases seen.

Flower buds were seen at about 10 weeks. I was away when they first appeared, but as far as I can tell it was about the same day. Salad blue potatoes have pretty lilac blue flowers with orange centres, making them an ornamental feature as well as a productive one.

They were harvested on the early side, before the top growth had fully died back. This is because I was again going to be away and wanted to have time to finish the comparison.

The yield was nevertheless as I would have expected. Potatoes grown in containers tend to yield on average about a quarter to a third of their yield in open ground. This is partly due to smaller tuber size, as the number of tubers is not so reduced.

Cooking and Tasting Salad Blue Potatoes

There was little difference in the weight of yield from F and N. There was a slightly higher number of larger tubers from N, but not many. This may have been more noticeable had I left them in the sacks for a while longer.

The rich blue-purple colour of Salad Blue potatoes in their raw state is pure delight. They turn the cooking water a blue colour but unlike so many coloured vegetables, the cooked potatoes still have a rich blue flesh.

I used my family as guinea pigs for the blind tasting as this was quickest. I presented the Salad Blue potatoes as lightly boiled for ease of tasting and testing. Firstly, just the potato, no salt, butter, mayonnaise, vinaigrette. There was a unanimous preference for the F, which was described as having a slightly nuttier flavour, which they all liked.

Once the potatoes (still kept separate) were presented as part of a meal, with additions of salt etc allowed, the two composts were even. The general consensus was that once other food items and seasoning were added there was little if anything to choose between them.

What everyone agreed was that they were flavoursome potatoes and why hadn’t I grown them recently?! It is probably about 5 years since I grew this particular variety on the allotment.

Whilst we eat a lot of fruit and vegetables, we’re not vegetarian, and we did enjoy a further meal with the Salad Blue potatoes and free-range Irish sausages and home-grown salad: mouth-watering!

Results and What Next…

Overall, Fertile Fibre gave a quicker start to the crop, consistently good growth and the expected yield. The potatoes grown in it were preferred for taste. It is the more expensive multi-purpose compost of the two, but it is recognised by the Soil Association. If organic soils are important to you as part of your organic growing, then you would give preference to this and other permitted products.

A little note on organic potting composts etc. If the packaging has the Soil Association logo then the product is recognised as being organic. Without the logo, the product hasn’t met these rigorous requirements. This is one of the reasons why organic foods and products cost more to produce, but it is important in maintaining standards and integrity. Without the logo a product is ‘organic’ in the sense that we humans are ‘organic’.

Having clarified that point, it is fair to say that New Horizon does not use green waste so is likely to be free of artificial herbicides. I would certainly use this over any growing media that wasn’t peat free. And as for the blue salad potatoes, there was not so much of a difference that I can categorically recommend one of the composts over the other. The choice, as always, is yours, I merely provide you with the information!

So, what next? There are some suggested articles for you below, and if you’d like a kitchen garden or vegetable plot designed, do please get in touch. Edible ornamental gardens are a delight for the eyes and a feast for the stomach and I’d love to help you enjoy one!