Six on Saturday: 11.7.20 soil science

I have been working on the next unit of my RHS Level 2 in Horticulture and I am currently looking at soil. So to gain a better understanding, I am looking at some of what I learnt to discuss my own garden. The hope being writing about it will cement some of the ideas in my head.

1. Soil type-Clay

My soil in both the front and back garden is clay. If you look at the geological map of my area my street is on a border area where it changes from sand to clay. But mine is definitely clay. You can dig it out and you can mould it into shapes. On the ribbon test, there is no doubt about what I’m working with.  The front is worse than the back but the back has been worked more since I moved in and had lots of homemade compost and other top dressings added. Clay soil is made up of fine particles. This makes it prone to waterlogging. It can be slow to warm up. Clay is usually high in nutrients, although sometimes these are in forms the plants can’t take in. When it is dry it is very difficult to dig as it dries like the bricks that are made out of it. By and large, I have followed Beth Chatto’s creed of ‘right plant, right place’. I have tried to plant things which suit my soil. I have tried plants in the past such as lavender which like a free draining soil by digging in lots of grit and sand. They survive but they don’t thrive so these have largely been removed to grow suitable plants. Plants such as hostas, astrantias and geraniums which are happy in these conditions.

2. Soil pH

I bought a soil probe to get an idea of my soil pH. I’ve tried it around the garden and my soil seems to be coming out around 5.5 placing it more on the acidic side of things. I don’t think it’s accurate though as this would mean my hydrangeas would come out blue and they come out pink. But it is nice to know as most of the larger plants I have should be comfortable within a range of neutral to 5.5 with the exception of the lilac which seems happy enough.

3. Peat free

A lot of the advice on improving soil online and in books still refers to using peat to improve the structure. Using peat is highly damaging to our environment. Peat is one of our best carbon stores so destroying peatland potentially increases climate change. So all my plants grown from seed, potted on and planted up in pots are grown in peat-free compost. I have used two main brands this year. Miracle-gro peat-free has been more readily available again and has been excellent. It has been selling outside Tesco recently which is good to see supermarkets starting to offer peat-free. It would be nice to know the plants they are selling are also peat-free The rate of germination for seeds has been great and plants in pots have grown well.

The second brand I use is Dalefoot composts. They offer compost for specific purposes growing seeds, veg, tomatoes and clay busting. The wool compost has been particularly good for the pots as it holds water well. If you look back on last weeks six you can see some dahlias thriving in it.

4. Clay buster

My front garden soil is compacted clay. When I first started the process of renovating it I had lakes forming in one corner each time it rained and the rate of drainage was incredibly poor. I do want a pond but not one that close to the front door. To improve the situation I did drill a number of holes that were filled with rubble and sand to create drainage spots. In the past, people would have double digged it in. The RHS course does go into the details of how to dig your two trenches, turn the soil, add more organic matter and fill your trenches but this is back-breaking work and evidence suggests it isn’t necessary apart from in the most severely compacted areas. By adding organic matter on the top the worms and other life in the soil will help take it in naturally. I added a top dressing in spring and it has helped. Adding in mulch in this way seems contradictory in some ways as adding a mulch improves water retention but also helps soil structure improving drainage. But the plants here seem to be growing happily and the ground does seem to stay moist now but not waterlogged. The true test will be autumn when we potentially get weeks of rain.

One of the best solutions I’ve found for the clay is adding Dalefoot’s clay buster. This is made from composted bracken. It helps improve the soil structure while also helping release the nutrients in the clay. In theory, a dressing like this only needs applying every other year but this was heavily compressed under gravel and weed matting for a decade or more so it is in need of a bit more work.

I had also left a bit of a dip having dug the dogwood out last week to replace with the Sambucus so I have used some of this to top-dress to feed the new growth and bring the soil level back up. When planting shrubs I normally avoid using compost in the planting hole as this can discourage the plant from rooting properly. If the plant is sat in nutrient rick soil it won’t bother to grow out so I tried to make sure it was sat in the existing soil and then used the fresh compost around the plant to encourage the roots to spread.

5. Ericaceous compost

While I have generally planted plants that suit my soil and conditions, there are some plants I like that don’t suit my conditions. I particularly like Acers though they don’t suit my conditions perfectly. While they are fine with the clay soil unless it is completely waterlogged and they are ok with the pH of my soil which seems to be slightly acidic they don’t like the winds much. For this reason, I have a number in pots where they can be moved to more sheltered positions than I can allow in my borders. Acers prefer more acidic soil so by growing them in a pot I can give them ericaceous compost to give them the most suitable conditions. This is my first time using Dalefoot’s ericaceous. It is made from sheep’s wool and bracken. This is supposed to contain a good level of nutrients suited to Acers as well as having the moisture retention they need. The pot is glazed. This makes it less breathable than a plain terracotta pot which lose more water from the sides. This should help with the water retention to help with the water loss from the sea winds.

6. Sequestered iron

I have had a number of acid-loving plants that have suffered from yellowing leaves, particularly those in pots. I believe this may be down to chlorosis, a lack of iron. This can be caused by a number of factors such as poor drainage or that the nutrients are in the soil but in a form the plants can’t access. In my case with my clay soil, I think poor drainage and possibly overwatering may be to blame. It has been so windy recently I have been watering to try to prevent the scorched leaves and crisped edges. To try to rectify the problem I have given the plants a liquid feed with sequestered iron to try to get the darker foliage back. The bottle suggests a feed every 2 weeks during the growing season so I’ll see how these are doing in two weeks.

I’ve just about finished the assignment for this part of the unit. I just have my plant profiles to work on over next week. So I’ll be looking at another 14 plants in-depth. My plant knowledge is increasing rapidly. I need to cover a variety of plants. So far I haven’t done enough annuals of roses so may need to look at more of them.

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17 thoughts on “Six on Saturday: 11.7.20 soil science”

  1. That was an interesting read. I might seek out the Dalefoot and Mircale-Gro composts. I’ve just been using New Horizon this year but a lot of seedlings have struggled to get going for some reason once they’ve germinated. It’ll be interesting to see if it was just bad luck or whether things do better in another compost.

    Liked by 1 person

    1. I’ve found new horizon mixed and that seems to reflect in other people’s experiences. Sometimes really good sometimes not. I found it poor on seed germination and that’s the main reason I buy compost so not ideal. A lot of seedlings just sat in pots not putting on growth so until I hear better reports I’ll probably avoid it.

      Liked by 1 person

  2. Well, I refrained from showing soil as one of my Six-on-Saturday ! Although I was going to show it at its infrequent best. Interesting to see all the different types of compost you use. I tend to keep buying horse manure which is fine for nourishment and improving the soil. I wondered about 6X chicken manure, not sure if it will help improve the soil texture. Interesting Six-on-Saturday again.


  3. What an adorable pH tester! I have clay soil in my back yard. I am not sure if it’s fertile like they say, since a lot of it doesn’t drain in winter and I don’t try planting in it. I use raised beds and containers. I love that blue crock like pot!


  4. It’s fascinating to read through as you study horticulture, & it certainly brings it all back – didn’t realise how rusty I’d become! Could do with a refresher course myself come to think of it!


  5. An interesting post. I suspect my soil leans towards the acidic, but I haven’t tested it. Since it was once part of the farmyard there is probably an awful lot of well rotted manure deep down! My biggest issue is the wind.


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