This post was most recently updated on March 26th, 2020
Nitrogen deficiency in bought manure based compost? Is that even possible? If so, what can I do to improve poor nitrogen levels in the soil?
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Last Winter I thought I was a genius. A very fat, heavily pregnant genius. Sick of my vegetable plants failing to grow and being overtaken by weeds in my vegetable patch, I decided to install raised bed and fill them with some commercial compost.
Now that Spring (and the baby) has arrived I have one big question – Why aren’t my vegetable plants growing??
Why are my plants in raised beds not growing?
Raised beds are touted as the premium garden option for the backyard vegetable grower, and with good reason (find out the importance of raised beds here). One of the main benefits is that you can fill the bed with better soil.
I would have thought that in a whole bed filled with compost, that was allowed to sit and rot down over Winter that my plants would be flourishing. But NO.
My vegetables are growing very slowly
Because I am a busy mum with 4 kiddies and I homeschool, my garden has been a little, let’s say ‘unwatched’ this year.
I have just managed to spend some time in the garden this weekend and found basically no growth on the transplants that I planted a whole month ago – I checked the dates in my gardening journal, it is a life saver!
Transplant shock can be one reason that the vegetables are growing very slowly, but I think there is something deeper going on here. I would have expected transplant shock to last no more than two weeks, then to see the plants start growing. But these plants have zero new growth on them after a whole month.
Why is nothing growing in my soil?
I would have thought that with a garden bed FULL of commercially made cow poop and sawdust compost, that my plants would be thriving!
If nothing is growing in your soil, you need to be observant and see what else is going on in the garden, and around it.
What I have also found very interesting is that the beans and peas that supply their own nitrogen are growing wonderfully. As are a few odd clumps of plants randomly placed in the raised garden beds.
These spots that are growing well just so happen to be the exact places we buried our old laying chickens before putting the compost in to the garden beds.
If nothing is growing in your soil, it does pay to do a soil test to check for low or high levels of micronutrients as well as toxic substances like lead. Low nitrogen is one common cause for poor plant growth in gardens. Poor drainage, dead soil life and dry soil are other causes.
10 Causes for bad soil and poor plant growth
This is the most common cause of no or low growth in vegetable plants. Plants show yellowing of the older leaves, and it starts from the tip of the leaf and works back. Brassicas like cabbage may also turn a little purple.
If your nitrogen levels are too high with fruiting plants you will get lots of lush green leaves and nothing much else.
Low phosphorus in plants is shown by the leaves and stem going purple and eventually dying off. The phosphorus is probably there but the soil is too cold for the plants to access it. Add some mulch to warm up the soil and you will probably be right.
Too much water
Very few plants like to be waterlogged. Unless you are growing rice paddies, it is best to make sure your puddles drain away quickly after rain to avoid vegetables having wet feet.
Too little water
Plants, especially when young, will be severely stunted or fail to grow entirely if they are starved of water. Most vegetables will need about an inch of water per week. Young plants need this spread out so they are watered at least every other day until they have established enough root system to find their own water.
Too many weeds will choke out your young plants. Some weeds can be indicators of poor growing conditions – mossy soil is acidic, buttercups grow in wet soil, dandelions indicate poor soil that is low in calcium, but high in potassium and crabgrass grows in very rubbish soil. More here
Fungal infections/Club root
If your brassicas are all going limp and dying off, you might have club root. Other fungal issues include mildew, rot and rust. Beneficial fungi in the soil help your plants grow, but these bad fungi will stop your plants from growing well.
Humus is the organic matter in the soil. Without it plants and microorganisms cannot survive. The best way of building your soil up is by adding compost and manures to improve your levels of humus.
Very few plants like high acidity environments, unless you are growing blueberries, azaleas or rhododendrons, you will want your soil to be between pH 6.5 and 7. Gypsum and lime with lower acidity.
Chalky soils tend to have a highly alkaline pH and plants will generally not do well in these soils either. Improve their pH by adding organic matter. Peat is particularly good at acidifying low acidity soils.
Read here on how to turn bad dirt into good soil.
A vegetable garden nitrogen deficiency
So by a process of sleuthing, I have decided that my commercial compost has caused a nitrogen deficiency in my vegetable garden.
Signs of low nitrogen in a vegetable garden: Chlorosis
The visual symptoms of nitrogen deficiency mean that it can be relatively easy to detect in some plant species. Symptoms include poor plant growth, and leaves that are pale green or yellow because they are unable to make sufficient chlorophyll. Leaves in this state are said to be chlorotic.
Chlorosis provides one of the first signs of a nitrogen deficiency your vegetable garden. The foliage/leaves begins to change color, usually first from deep green to a paler shade of green, or it develops a blue/purple shade in some plants. As the deficiency continues and the chlorosis intensifies, the leaves begin to turn yellow and they will wither and die.
Leafy vegetables are worst affected by low nitrogen in the soil. Vegetables that form relationships with mycorrhizal fungi like peas, beans and other legumes are less likely to be affected.
Wood based compost causing light leaves
It is well known amongst the Back to Eden growing community that wood mulch when it is broken down it adds nitrogen and nutrients to the soil, but you have to be careful not to mix the wood mulch in to the soil as it robs the soil of nitrogen as it breaks down when it is mixed in.
This is also why you make sure to plant right down in to the soil, not in the wood mulch, so the plants can access the soil nutrients.
While compost that contains woody materials are breaking down, you will need to add additional nitrogen to your garden.
Is commercial compost low nitrogen?
Most commercial compost mixtures are wood based. This is because it is a scrap product for many industries and it breaks down to make amazing soil.
The issue is that commercial composts and potting mixes usually are not broken down enough when you buy them. They will often add some synthetic, short term fertilizers that should get your plants through until the wood is broken down enough, however this is not always the case.
My plants poor growth, and light leaves are being caused by the sawdust and cow manure compost that I filled the raised beds with not being broken down enough to be releasing the nitrogen and other nutrients to my plants yet. So in years to come, my gardens will thrive, but this season, I am going to have to add more nitrogen to the compost to keep it breaking down and feeding my plants.
How do I add nitrogen to my vegetable garden?
If your plants are already showing signs of nitrogen depletion, a foliar spray is the best way to increase it immediately. It will not cure the already affected leaves, but it will allow new, green growth to come more quickly.
A foliar spray once a week as well as some of the slower method below will fix the short and long term issue of low nitrogen in the soil.
1. Composted manure
Adding more composted manure to the soil will improve the nitrogen levels, avoid adding more woody material
2. Chicken poop
Chicken and other poultry manure is particularly high in nitrogen, it should be composted before use. See here on using chicken manure in the garden.
3. Soybean or cottonseed meal
If you can get spent seed meal, most seeds are high in nitrogen, you can add them to your compost or add them as a mulch to your soil.
4. Planting a green manure crop
If you have time planting a green manure crop and digging it in will increase the nitrogen levels in the soil. Adding lawn clippings can help as well.
5. Planting nitrogen fixing plants
If you can, use some companion planting methods and add some legumes to your gardens like peas or beans
6. Adding coffee grounds to the soil
While coffee grounds look brown, they are actually very high in nitrogen and are considered a ‘green’ when building a compost pile.
7. Adding liquid fish emulsion
Liquid fish emulsion is probably one of the best ways of naturally adding nitrogen to your plants and soil. You can get it here. If you have a fish tank, when you clean them out, that water is also high in nitrogen.
8. Adding blood and bone
9. Seaweed tonic
Kelp as a liquid can be use used as a general foliar tonic, or used to increase nitrogen and other nutrients in the soil. You can also get it in powered form to add to the soils to slow release. Grab it here or here
Fresh urine is high in nitrogen, moderate in phosphorus and low in potassium and can act as an excellent high-nitrogen liquid fertilizer or as a compost accelerator. Dilute it 1 part urine to 4 parts water and spray it on your plants. Or pee directly on the compost heap!
If your plants are showing yellowing leaves or slow growth is probably you have a nitrogen deficiency. Use some of the above methods to improve your nitrogen levels and see your plants flourish.
If you are new to gardening you should check out our beginner gardening course – we hold your hand for a whole year, telling you what to plant and when, as well as educating you along the way. Find out more here.
For further reading, I really recommend all of these books. I own every one of them and they are amazing resources!