How deep should you plant bulbs?

Pure white ‘Stanless’ is planted in front of large camellias which provide a startling dark backdrop and rich red flowers

Bulb-planting season is in full swing. Now is the perfect time to plant as many bulbs as you can, to be sure of a bright spring. All the small bulbs should be put in as quickly as possible but tulips can be left until November before planting.

But how deep and how close should you plant your bulbs. The general rule of thumb is that bulbs should be planted about two and a half times their height below the surface. In fact, this works well for smaller bulbs and corms but can be a problem with ‘tall’ bulbs such as daffodils. These are frequently 10cm tall and they don’t need 25cm (10in) of soil over their tops.

You may have seen, or even bought, pots of daffodils in bud, often from supermarkets, with the bulbs completely exposed on top of the pots. So how is this possible? Well the pots of bulbs are either kept in the dark till the shoots are well grown or they are plunged (buried) in sand or compost until the shoots are grown and they are brought into the light.

In our gardens, and in containers, if bulbs are planted close to the surface, it will not usually affect their flowering in the first spring – that is all sorted out by the bulb grower. But after blooming, a common problem of shallow planting is that the bulbs split into lots of smaller bulbs and these may not be large enough to flower.

Most bulbs have the ability to adjust their height in the soil – well to drag themselves deeper anyway. They produce special roots that are thicker than usual and these attach themselves at the base and then shrink, pulling the bulbs into the soil. This is necessary because, in the wild, the seeds germinate on the surface and they need a mechanism to get those bulbs deep into the soil. Large bulbs are more difficult to pull down so it makes sense for the bulbs to split into many small bulbs, if near the surface, so they can be pulled down.

So, if you do get the planting depth wrong, as long as it is not extremely deep, your bulbs will sort themselves. A good reason for planting reasonably deep is that if you have other plants among them, you can plant above them, from June to December, without risking damaging the bulbs or shoots.

But how far apart should you plant them?

I would say that, if you are planting for immediate impact and the bulbs will be lifted after the first spring, whether in pots or in bedding, you should put them close, perhaps 10cm apart for daffodils and 12cm for tulips but, in the garden, if they are to be planted permanently, I would put them 20cm apart, to give them room to grow.

When you buy daffodils, they can vary from single-nosed bulbs to those that are clusters of small bulbs. These smaller bulbs may not be of flowering size. Big, single-nosed bulbs will have the best flowers. In the garden, and for naturalising, the bulb size does not matter too much – they will all flower in a year or two. But big bulbs are best for pots, where you want the maximum display in the first year. But bear in mind that not all daffodil varieties naturally have huge bulbs – just choose the biggest bulbs of each variety.

Jobs for the week

Weigela ‘Wings of Fire’

Plant for autumn colour.

Berries are the highlight of our gardens in autumn but autumn foliage plays its part too. A recent addition to my garden is weigela ‘Wings of Fire’, a recent introduction that is grown for its foliage rather than its (lavender) flowers. The caramel colour of the leaves gets more intense as summer progresses, culminating in dazzling foliage right now.

Cut back perennials.

As perennials lose their leaves and beauty, cut them back to keep the garden tidy. Pull up old vegetables too to prevent leaving food for slugs and other pests.

In the greenhouse

Pick the last of the tomatoes and make soup or chutney. On wet days, sort out all those pots and clean them and put them away for spring. I was doing this yesterday and though I always dread starting I am so pleased when it is done!

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