This has been a really tough spring for transplanting. The wind has been unrelenting and the frosty nights mean extra work. However, with well hardened-off plants you will be three steps ahead, and the plants will make the transition much more smoothly.
When plants are moved, they face a new set of challenges, mostly about uptake of water.
If they are bare-rooted then they need to establish a good contact with the soil so that they are anchored and wont blow over, breaking roots and limiting water uptake.

You can help establishing contact by 1) really firming the soil around the plant and 2) watering once the plants are in. I worked under a head gardener who would come and give any transplant a good yank, and if it came out then I had to do the whole job again.
The watering may not be needed in terms of the amount of moisture in the soil, but it is vital in order to establish good contact between tiny soil particles and the tiny roots. Those tiny roots are the ones that absorb moisture which also contains nutrients. We know water keeps the leaves from wilting. Wilting leaves won’t draw energy from the sun.

However, wilting does often happen, and you support the plant by creating as humid an environment around it as possible. This can take the form of erecting a barrier against the wind such as a cloche or an impervious surround, or by misting frequently with a sprayer.
You are aiming to create still humid air so there is no diffusion out of the leaves. Plants absorb water at root level and lose it from their leaves, and we aim to keep both roots absorbing and leaves turgid (full of water). Turgid leaves can photosynthesize and gather the sun’s energy.

You will help the plant greatly by making sure it is fully hydrated before planting it out, whether it is pot-grown, from a seed bed, or a transplant from another part of the garden.

Pot-grown plants seem to be easier to transplant. You can plant them any time of year when soil conditions are suitable, ie not waterlogged, not frozen. Roots need to absorb moisture.

Few plants were sold in pots until about 40 years ago, and this change revolutionized the nursery trade. Sales could go on during the summer months when plants were in full leaf and flower. It enabled us to see what a plant would develop into.
Pot-grown plants need special consideration. Heathers are an extreme case and sadly many have died for lack of appreciation of their needs. Watering is key.

Have you ever let a sack of compost or a pot plant dry out? You will know just how difficult it is to re-wet that compost. The water rolls off and refuses to be absorbed, and the only solution is to stick the whole pot into a bucket and leave it till the compost is wet.
I mention this because when you plant a pot-grown plant, its roots are all contained in the pot-shaped rootball. They don’t immediately grow out into the surrounding soil, especially if the soil is cold. So your watering must include both the rootball and the surrounding soil. Until new roots have grown, the rootball will dry out as quickly as it did in the pot.

I have found that new transplants appreciate any initial help as outlined above, and as they grow and toughen/adjust to their new surroundings the extra props can be withdrawn. May frequently looks like a ‘war zone’ in our garden, with nets, cloches, fleeces, even corrugated iron or old windows to provide that shelter (apologies to any who have been in a real war zone).

You will see in the literature that there are times to transplant evergreen shrubs and other times to transplant deciduous shrubs. It is only in the temperate climates in the northern hemisphere that the deciduous plants drop their leaves in winter. In the hot dry climate of the Mediterranean or South Africa, many plants drop their leaves in the summer.

Why is this? The reason leaves are jettisoned is usually to prevent water loss. In our climate, the ground can freeze for weeks and roots can’t absorb water. The leaves lose water as they normally do but they don’t get supplied with fresh water by the roots. They dessicate (dry out). To prevent water loss, they drop leaves in autumn. In climates with a hot dry summer, water becomes scarce and leaves drop in the dry season.

Around this time of year we start to notice damage to some evergreens: they begin to look scorched after a hard winter (pictured). Perhaps they have been frosted, or come through the winter looking green but then die as the weather has warmed up. Their gamble of retaining their leaves hasn’t paid off, and the whole plant has lost too much water to survive.

The advice to prevent this is the same as the advice given for newly planted evergreens. Give them shelter to try to prevent water loss from their leaves, and frequent watering should go on for an extended period. How long?
The temperature of the soil and the hardiness of the plant both come into play here. The roots of a bare-rooted and hardy transplant are likely to start growing as the soil warms, as long as it is moist. Water so the roots grow more quickly and keep up with the demands of leaves. The plants will establish and grow at whatever rate the soil and air temperatures dictate. Water new transplants daily if the soil is dry, easing off to every few days then to once a week until rain re-wets the soil and the plants’ roots delve down deep.

The roots of a tender plant may not adapt quickly enough unless you have warmed the soil beforehand by using a cloche or polythene laid flat onto the soil. If you are unsure of how tender a plant is, look up its ancestry. Tomatoes and peppers, for instance, are from Central America, either side of the equator. Read ‘Warmth’.

Tender plants won’t tolerate frost. But neither can they tolerate a temperature just above frost. Have you ever put bananas in the fridge? They signal their disapproval by going black. This is called a ‘chilling injury’. They simply have no adaptations in their physiology to tolerate temperatures that are too low.

For all sorts of reasons transplanted plants will ‘sulk’, and while this isn’t a technical term you will often see it in books and magazines. The plants are unhappy, and as we are aiming for bonzo crops we need to address their needs right through to harvest.
I grow a variety of cacti and succulents; I find them fascinating. They enjoy going outside in the summer and look refreshed for the change. But I cannot put them out until early July. Any earlier and they turn olive or blue which really does not look great.
Tomatoes, chilies, peppers and their friends benefit from being potted up repeatedly until the weather is warm or until you can provide sufficient protection and warmth. This means there will be no check to their growth.

I plant aubergines and chillies in my polytunnel, but as I keep it well ventilated to prevent disease I can’t plant them out till early July, at which point they don’t look back. Oddly tomatoes have never done well in the polytunnel, so they remain in the glasshouse (more light?).

Water supply is said to be the greatest impediment to growth worldwide. We live in Scotland, so although there are droughts for short periods, defined as 10 days without rain, let’s not hold back. Water generously. Give them shelter until established. They will love you forever!