3

Problem My new front garden seems to have pools of water on it for a good few hours after rain.

Background I've just had the front garden redesigned, leaving us with a brand new area for planting and a new driveway. The area where the garden now is is our old driveway. The old tarmac drive was broken up, but left. Underneath the tarmac is solid chalk. Retaining walls have been built around this to effectively create a raised front garden to a height averaging 0.8 - 1.5m deep.

The infill is made up of a lot of rubble from the building works, like tarmac, bricks etc. Then there is some average quality soil, and finally a good 400mm of fresh graded topsoil.

The whole garden is to be used as a bed for planting topiary, shrubs etc - no lawn. We have planted lots of buxus already. 24 hours after watering, the soil still feels very sticky. Is this due to poor drainage? With all that rubble at the bottom, some ungraded soil (200mm perhaps?) and then 300-400mm of topsoil, I thought I would have good drainage.

Photos

Before adding topsoil (the large rubble was removed)

After the topsoil was delivered

Question

Can anyone explain why I would be seeing puddling of water after rain? Is this something I should worry about, or is this just usual for topsoil as it starts to compact down after delivery.

Any help and advise appreciated as I really don't want all this money to go to waste due to a mistake I've made so early on. So would rather try and rectify now if there is anything that needs doing.

  • What part of the world are you in please? And when you say 'average quality soil', where did that come from and how deep is that layer? And please clarify re the tarmac - when you say 'broken up but left', how was it broken up - do you mean it just had holes punched into it and otherwise left as a surface covering, or something else? What would you say was the ratio of rubble and tarmac left in there - enough to cover the whole area? Are there large pieces of rubble? Are there weepholes in the mortar of the wall at the front where it meets the pavement/sidewalk? – Bamboo Mar 13 at 9:49
  • We're in the UK.... Guildford, Surrey which is very very chalky. By average quality, I mean it wasn't graded, and was just lifted from a nearby job and used to fill the garden. Using graded topsoil would have been very expensive for me. You can see that soil in picture 1. The depth varies, but 300mm is my best guess. The tarmac was basically ripped up by digger and jack hammer, but left in large bits at the bottom. It was then filled with chalk and general rubble from where the rest of the garden was dug out. – mcampster Mar 13 at 19:44
  • If the average depth of the site before reaching the tarmac is 1100mm, I reckon its made up of 500 rubble/chalk/broken tarmac, 300 ungraded soil and 300 top soil. And yes, there are definitely some large pieces in there... the old wall was made from local stone and that's in there, broken but still significantly bigger than a brick. There are 4 weep holes sitting a few inches above ground level. I will try and post some other pictures that show the profile of the land. – mcampster Mar 13 at 19:44
  • have you tried composting a lot of wood chips in the area to build soil health, as it looks like the soil is dead? – black thumb Mar 13 at 22:38
3

I thought you were probably in the UK... First, let's just establish that we've had a fair bit of rain in the last few days with these storm conditions, so that might account for puddles for an hour or two, but no, it's not usual for puddling to remain for any longer than that because the soil 'hasn't settled', in fact, quite the opposite. You say the original surface and soil was over solid chalk - chalk does drain and in fact, can cause drought issues during summer. The usual advice is to make a few holes in the chalk if its a solid sheet to break it up a bit, because although water does percolate through, getting some organic matter into it helps the area to retain water and creates higher fertility, a lack of which can be an issue on chalk.

I suspect the problem you're having is (first) being caused by the sheer amount of large and medium debris - it would have been best to remove as much as possible of the tarmac, and only leave in there stones or stony bits under 2/3 inches in size. The second possibility is that some of the soil you've put in there is clay based, and that will puddle during very wet weather. If you've used heavy clay soil beneath the graded/screened topsoil, it will still cause a problem in very wet weather, such as we've had. It may also be that the graded topsoil has no or a very low loam content and therefore a higher clay content, and that won't help either, though clay in and of itself is higher in nutrients than chalk, so that's not all bad. I note you do not mention adding anything organic such as composted manure, spent mushroom compost, good garden compost, soil conditioning compost or any other type of organic composted material - as much of that as possible should really be mixed in, especially over solid chalk.

I am loath to suggest you take it all out and start over, removing the larger debris, but I do think you should 'unplant' the plants and work as much organic material as possible into what's there, at the same removing any large lumps of debris you can locate whilst doing that. This link https://www.rhs.org.uk/advice/profile?pid=763 on plants for chalky soils also gives some brief advice on how to improve chalk based soil, as well as listing plants that will cope in chalk conditions. This blog https://www.learningwithexperts.com/gardening/blog/soil-preparation-and-improvement also covers what to do with various types of soil in order to make them not only better draining, but more fertile, so you may want to read that too.

Ongoing, I'd recommend the addition of organic material at least annually - once you've sorted it out and planted up, you can just lay it over the top of the soil as a mulch once or twice a year, and nature will work it into the soil for you.

  • The only soil I suspected of having a high clay content is the top soil. It looked great on day 1, but after the rain it is very clumpy, not very granular. But I phoned the company up and they said it should have a very low clay content, although I suspected he wasn't entirely sure himself. You are right about composting, I should have had a tonne bag delivered and worked in. Instead I have been working in compost local to each plant - household compost, rootgrow, blood fish & bone etc. – mcampster Mar 14 at 14:56
  • What I can't understand is how this happened so quickly! The site is over 1m deep. Whilst we've had lots of rain, its only been in there for 10 days. Surely the rubble can't be an influencing factor just yet? If I've got 600mm+ of soil on top of the rubble, would that not take a long time to start backing up and restricting drainage? – mcampster Mar 14 at 15:00
  • I reckon its a high clay content topsoil... a lot of delivered topsoil is just motorway spoil with the larger stones screened out if you paid for a higher grade, and that's most always high in clay. Clay soil takes days to dry out, not helped by large chunks of rubble beneath the layers... the trouble with even lots of stones in soil is that, over time, they end up clumped together, forming what seems to be an impenetrable layer when you try to dig. The only way to clear those accumulations is by using a fork rather than a spade and working the layer loose and then removing the larger pieces – Bamboo Mar 14 at 15:23
  • As for the supplier, if he can't tell you the ratios of loam, sand and clay, you've just got bog standard clay topsoil with larger lumps screened out I'm afraid. Adding horticultural grit by the bagful, along wth lots of composted material will help. – Bamboo Mar 14 at 15:25
  • Thanks Bamboo, I reckon you're probably right about the supplier, and I've got a load of clay in it. So now I'll read those threads and see what I can do to improve the drainage of high content clay soil. – mcampster Mar 14 at 18:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.